*****TBD*****

This subclass is indented under the class definition. Systems comprising (a) two or more wave transmission lines or networks, each line or network being operable to separately propagate wave energy or (b) means for effecting an interchange of wave energy from one transmission line to two or more transmission lines or vice versa, or having a coupling network for effecting an interchange of wave energy from a single input to plural outputs or vice versa, together with means for controlling or facilitating the interchange of energy.

(1) Note. The term "network" as used above denotes any of the systems defined in the class definition, subsection A.

(2) Note. Included in (a) above are systems having two distinct transmission lines, each line being operable to transmit wave energy electrically distinct from that propagated by another of the transmission lines, and also lines which are distinct but not necessarily simultaneously usable to transmit electrical wave energy (e.g. one line may be used to substitute for another as in subclass 3). The two or more transmission lines may have a common conductor, see especially subclasses 4+ where a balanced circuit is involved.

(3) Note. Included are lines which transmit energy from a first point to a second spaced point and provided with means to transmit a portion of the energy to a second line (e.g. a tapped line).

(4) Note. This and the indented subclasses do not provide for systems where a signal is divided among two transmission lines or networks and then recombined on a single line or to provide a single output. Such systems and networks are found in subclasses 12 et seq. If the system claimed does not extend to the recombining part of the line or network, the patent is classified in this or the indented subclasses.

(5) Note. A system with a single communication transmission line and also a pilot line which is a long line within the class definition and which transmits wave energy is classified in this or indented subclasses.

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15,	for a system having a single transmission line and pilot line to sense only ambient conditions (temperature, humidity).

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174,	Electricity: Conductors and Insulators, appropriate subclasses for electrical conductor structure adapted for use in plural channel systems other than loaded lines or transmission lines defined as having long line characteristics.
178,	Telegraphy, appropriate subclasses for plural channel systems involving telegraphy, note subclass 45 for plural channel systems using a loaded line.
307,	Electrical Transmission or Interconnection Systems, particularly subclasses 11+ , 43+, 113+, and 147+ for miscellaneous electrical distribution systems involving plural channels.
330,	Amplifiers, subclass 295 for plural channel transistor amplifiers, subclass 69 for sum and difference amplifiers, subclasses 73 and 74 for series arranged amplifiers with plural outputs and plural inputs, respectively, subclass 84 for plural channel amplifiers having feedback, subclasses 124+ for plural channel amplifiers generally, subclasses 147 and 148 for amplifiers having plural inputs and plural outputs, respectively. See especially, subclasses 54 and 286+ for "distributed amplifiers."
334,	Tuners, appropriate subclasses for tuners, per se.
340,	Communications: Electrical, appropriate subclasses for miscellaneous electrical communications, including signalling systems, involving plural channels. Note particularly subclasses 870.11+ , and 870.41, and 870.27 for continuously variable indication communication systems involving plural transmitters, plural receivers, and plural circuits respectively.
343,	Communications: Radio Wave, particularly subclass 771 for plural slot type antennas with wave guide coupling; subclasses 814 and 816 for plural balanced doublet type antennas with a coupling network; subclass 852 for antennas with a plural path coupling network with impedance matching; subclasses 853+ for plural antennas with a coupling network; and subclass 858 for antennas coupled to plural leadins.
370,	Multiplex Communications, subclass 200 for a phantom circuit, and subclass 308 for a resonant transfer technique used in the multiplex system.
379,	Telephonic Communications, appropriate subclasses for plural channel systems involving telephony, see subclasses 338+ for circuits having a two-way repeater (amplifiers) therein.
439,	Electrical Connectors, particularly subclasses 775+ , 865+, 869+, 874+, 877+, 883, and 884+ for various types of electrical connections and terminals.
455,	Telecommunications, appropriate subclasses for modulated carrier communication and radiotelephone communication systems, which may include wireless distribution and plural channel radio communication systems.

1.1	. Nonreciprocal gyromagnetic type (e.g., circulators):

This subclass is indented under subclass 1. Systems which include gyromagnetic elements for effecting a nonreciprocal interchange of electrical energy among the transmission lines or through the coupling network.

(1) Note. The term "gyromagnetic" as applied to material designates magnetically polarized material (e.g., ferrites, garnets, ionized gases) having unpaired spin systems which exhibit significant precessional motion in an orthogonal R.F. field. The term "nonreciprocal" designates a particular interchange of electrical energy that does not satisfy the reciprocity theorem. For example, a nonreciprocal interchange exists when the electrical output at a first set of terminals of a network produced by an input at a second set of terminals of the network does not equal the output at the second set of terminals produced by the same input applied at the first set of terminals. The term "circulator" (to which most of the patents in this subclass pertain) designates a device with at least three terminals wherein power entering at terminal 1 exists at terminal 2 only, power entering at terminal 2 exists at terminal 3 only, and power entering at terminal 3 exists at terminal 1 only.

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24.1,

24.2 and 24.3, for single channel coupling networks including gyromagnetic material for effecting a nonreciprocal transfer of electrical energy.

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330,	Amplifiers, subclasses 4 , 4.8 and 63 for amplifiers using gyromagnetic elements.
455,	Telecommunications, subclasses 318+ , for mixers using gyromagnetic elements.

2	. With automatic control:

This subclass is indented under subclass 1. Plural channel systems having means to sense a condition in the system and to control the operation of the system in accordance with the condition so sensed.

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17+,	and the subclasses specified in the notes thereto for single channel automatically controlled systems and networks.

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307,	Electrical Transmission or Interconnection Systems, particularly subclasses 39 , 86+, 116+, and 326+ for miscellaneous plural channel electrical transmission or interconnection systems which involve automatic control.
323,	Electricity: Power Supply or Regulation Systems, subclasses 234 through 303for condition sensing regulators.

3	.. Line substitution:

This subclass is indented under subclass 2. Systems comprising at least one normally operative wave transmission line and a spare transmission line, and automatically operable means associated with the transmission lines for using the spare transmission line in place of the normally operative transmission line upon failure of the normally operative line.

(1) Note. Systems for automatically substituting a particular device or system for a normally operative device or system are in general classified with the particular device or system. For example, systems for substituting repeaters in a two way repeater system are classified in Class 379, Telephonic Communications, subclasses 338+ and systems for substituting for defective amplifier system or a part of an amplifier system (such as a vacuum tube) are classified with the amplifier systems in Class 330, Amplifiers, subclasses 84 and 124+.

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13,	for resonator type breakdown discharge systems which control the transmission over a line.
100+,	for branched circuits with nonautomatic transmission line switching.
262+,	for transmission line elements, which may include switching devices.

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307,	Electrical Transmission or Interconnection Systems, particularly subclasses 23 , 39, 64+, and 80+ for miscellaneous electrical systems of distribution which involve automatic substitution of electrical load circuits or supply circuits.
331,	Oscillators, subclass 49 for plural oscillator systems wherein one oscillator may be substituted for another.

4	. With balanced circuits:

This subclass is indented under subclass 1. Systems wherein at least one of the transmission lines is a balanced line, or having a network which is especially designed for connection to at least one balanced circuit.

(1) Note. A balanced line or circuit is a line or circuit having its conductors electrically symmetrical with respect to a reference potential plane (e.g. ground).

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12,	for transmission line inductive or radiation interference reduction systems, involving a balanced transmission circuit.
25+,	for coupling networks for coupling a single channel balanced circuit to an unbalanced circuit.
236+,	for single transmission lines of the long line type, which may be balanced.

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174,	Electricity: Conductors and Insulators, particularly subclasses 32+ , 37+, 40+, and 68.1+ for electrical conductor structure of the electrically balanced type other than loaded lines or transmission lines defined as having long line characteristics.
307,	Electrical Transmission or Interconnection Systems, particularly subclasses 12+ , 42 or 147+ for miscellaneous electrical transmission or interconnecting systems which include balanced circuits.
343,	Communications: Radio Wave Antennas, subclasses 814 and 816 for plural balanced doublet antennas with coupling networks; and subclass 865 for a balanced antenna with a balanced coupling network.
363,	Electric Power Conversion Systems, particularly subclasses 2+ , 9+, 36, and 148+ for balanced phase conversion systems for converting electrical energy from one number of phases to a different number of phases (e.g., single phase to polyphase).
365,	Static Information Storage and Retrieval, subclass 202 for complementing or balancing signals used in a read/write circuit.
370,	Multiplex Communications, subclass 200 for a phantom circuit used in the multiplex system, and subclasses 278 and 282+ for a duplex system which may include a balance circuit.
379,	Telephonic Communications, for telephone systems which involve balanced transmission lines.

5	.. Plural balanced circuits:

This subclass is indented under subclass 4. Systems having a plurality of balanced transmission lines or having a network which is designed for connection to a plurality of balanced circuits.

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25+,	for coupling networks for coupling a single channel balanced circuit to an unbalanced circuit.

100	. Having branched circuits:

This subclass is indented under subclass 1. Systems including means for effecting an interchange of wave energy from one transmission line to two or more transmission lines, or vice versa, or having a coupling network for effecting an interchange of wave energy from a single input to plural outputs, or vice versa, of energy together with means for controlling or facilitating this interchange of energy.

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2+,	for plural channel branched circuit systems having automatic controlled means to control the system.
4+,	for plural channel systems and coupling networks wherein at least one of the transmission lines is a balanced line or where the network is especially designed for coupling to at least one balanced line.
13,	for resonator type breakdown discharge circuits which include a space discharge device designed to breakdown in response to high level energy (e.g., from the transmitting section of the system) to block substantially the flow of high level energy, and to pass low level energy along the transmission line (e.g., to a receiver). The devices in subclass 13 include T-R and R-T systems.

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174,	Electricity: Conductors and Insulators, particularly subclasses 38 , 43, 49, 71+, and 520 for branched electrical conductor structures other than loaded lines and conductors defined as having long line characteristics.
307,	Electrical Transmission or Interconnection Systems, particularly subclasses 11+ , 43+, and 147+ for miscellaneous electrical distribution systems which include branched circuits.
327,	Miscellaneous Active Electrical Nonlinear Devices, Circuits, and Systems, subclasses 407+ for miscellaneous circuits for use in coupling plural channels to a single channel.
331,	Oscillators, subclasses 60+ for an electrical oscillation generator provided with plural output circuits.
343,	Communications: Radio Wave Antennas, subclass 771 for plural slot-type antennas with wave guide coupling; subclasses 776+ for plural waveguide type antennas with coupling; subclasses 814 and 816 for plural balanced doublet type antennas with a coupling network; subclasses 853+ for plural antennas generally with a coupling network; subclass 858 for antennas coupled to plural lead-ins.
375,	Pulse or Digital Communications, subclasses 268+ , 353 for duplex systems having an antenna coupling network coupling a transmitter and a receiver to an antenna.
439,	Electrical Connectors, subclasses 150+ and 242 for multiple connector structure; subclasses 241+ for line tapper connector structure such as alligator clips and test probes.
455,	Telecommunications, subclasses 132+ for antenna coupling networks for plural receivers where the coupling network includes an active element and/or significant receiver structure; and subclasses 103+ for similar subject matter for transmitters.

101	.. Including switching means:

This subclass is indented under subclass 100. Systems with means for abruptly connecting and disconnecting two or more transmission lines to or from another transmission line.

(1) Note. The systems in this subclass usually having means to reduce reflected waves resulting from impedance discontinuities or irregularities caused by the presence or operation of the connecting and disconnecting means.

(2) Note. Plural circuit switches restricted to use in a particular art are sometimes classified with the art, for example, switches in telegraph systems and switches in telephone systems are classified elsewhere.

(3) Note. Variable power dividers which are classified below normally have a continuously variable transfer of power which is not abrupt.

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2+,	for similar systems having automatically controlled means.
3,	for automatically controlled line substitution systems.
13,	for single channel resonator type break-down discharge systems where the resonator-discharge device is used to effectively short circuit or open circuit the line (e.g., R-T or T-R systems).
258,	and 262, for transmission line elements for single channels which may be used to perform a switching or blocking function.

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178,	Telegraphy, for switches in telegraph systems.
200,	Electricity: Circuit Makers and Breakers, particularly subclasses 1+ and 19.01+ for plural circuit switches of general utility and not limited by claimed structure to use with long lines.
307,	Electrical Transmission or Interconnection Systems, particularly subclasses 23 , 38+, 64+, 80+, 85+, 98+, and 112+ for miscellaneous electrical distribution systems which include switching.
331,	Oscillators, subclass 49 for plural oscillator systems provided with means for selectively connecting one or more of two or more oscillators to a common output circuit.
379,	Telephonic Communications, for switches in telephone systems, especially subclasses 242+ .

102	... Having gyromagnetic operating means:

	This subclass is indented under subclass 101. Subject matter whereby a gyromagnetic element, e.g., fettile, is used as the switching element.

103	... Having semiconductor operating means:

	This subclass is indented under subclass 101. Subject matter whereby the switching means is a semiconductive element (e.g., diode).

104	.... Using TEM lines:

This subclass is indented under subclass 103. Subject matter whereby the dominant mode in the transmission lines is of the type having only transverse electromagnetic components.

(1) Note. Examples of such lines are coaxial lines, striplines, and microstrip lines.

105	... Having mechanical switching means:

This subclass is indented under subclass 101. Systems wherein the means for abruptly connecting and disconnecting two or more transmission lines to or from another transmission line is a mechanical element.

(1) Note. The systems in this subclass usually have means to reduce reflected waves resulting from impedance discontinuities or irregularities caused by the presence or operation of the connecting and disconnecting means.

(2) Note. Plural circuit switches restricted to use in a particular art are sometimes classified with the art, for example, switches in telegraph systems are classified in Class 178, Telegraphy, and switches in telephone systems are classified in Class 379, Telephonic Communications, see especially subclasses 242+.

(3) Note. Variable power dividers normally have a continuously variable transfer of power which is not abrupt.

(4) Note. Examples of the types of mechanical elements used are movable shorting pins, rotating assemblies, and movable transmission lines.

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2+,	for similar systems having automatically controlled means.
3,	for automatically controlled line substitution systems.
13,	for single channel resonator type breakdown discharge systems, where the resonator discharge device is used to effectively short circuit or open circuit the line (e.g., R-T or T-R systems).
262,	for connection and disconnection of long lines.

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200,	Electricity: Circuit Makers and Breakers, particularly subclasses 1+ and 19.01+ for plural circuit switches of general utility and not limited by claimed structure to use with long lines.
307,	Electrical Transmission or Interconnection Systems, particularly subclasses 23 , 38+, 64+, 80+, 85+, 98+, and 112+ for miscellaneous electrical distribution systems which include switching.
331,	Oscillators, subclass 49 for plural oscillator systems provided with means for selectively connecting one or more of two or more oscillators to a common output circuit.

106	.... Using rotary switching means:

	This subclass is indented under subclass 105. Subject matter wherein the mechanical element rotates about an axis through the switch device.

107	..... For TEM lines:

	This subclass is indented under subclass 106. Subject matter whereby the dominant mode in the transmission lines is of the type having only transverse electromagnetic components.

108	.... For waveguide:

	This subclass is indented under subclass 105. Subject matter whereby the transmission device propagates electrical waves having and electric or magnetic field component extending in the direction of propagation.

109	.. Using directional coupler:

This subclass is indented under subclass 100. Wave transmission systems including two transmission lines having an intervening coupling which propagates a portion of the energy passing in one direction along the first line in the second line in only one direction from the coupling, and which propagates a portion of the energy which may pass in the other direction along the first line in the second line in the opposite direction only from the coupling.

(1) Note. The second line may include a means, such as a dissipative termination, so that the energy from one direction only will be propagated to a distance in the second line. For example,

Image 1 for class 333 subclass 109

Image 2 for class 333 subclass 109

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117,	for a plurality of lines connected to a line by means of a hybrid coil.

110	... For providing frequency separation:

	This subclass is indented under subclass 109. Subject matter wherein the interchange of energy results in the separation or combination of a plurality of frequencies or frequency bands.

111	... For providing adjustable coupling:

	This subclass is indented under subclass 109. Subject matter wherein the amount of electromagnetic energy transferred between the first and second transmission lines can be changed to provided a different coupling ratio.

112	... Having lumped parameters or impedances:

This subclass is indented under subclass 109. Subject matter wherein an impedance element is included which may be considered as concentrated at one point.

(1) Note. See the class definition for the definition of "lumped parameters" or impedances.

113	... Having parallel-guide waveguide:

	This subclass is indented under subclass 109. Subject matter wherein the first and second transmission lines are waveguides; the direction of energy propagation in the first and second lines being parallel in the coupling region.

114	... Having crossed-guide waveguide:

	This subclass is indented under subclass 109. Subject matter wherein the first and second transmission lines are waveguides; the direction of propagation in the first and second lines being transverse to each other in the coupling region.

115	... Having TEM lines:

	This subclass is indented under subclass 109. Subject matter wherein the first and second transmission lines are the type having only transverse electromagnetic components and no longitudinal electromagnetic components as their primary mode of operation.

116	.... Using stripline:

	This subclass is indented under subclass 115. Subject matter wherein each of the first and second transmission lines have a planar center conductor and a planar ground plate.

117	.. Including hybrid-type network:

This subclass is indented under subclass 100. Systems including coupling one wave transmission line to two or more wave transmission lines in such manner that there is a conjugate relation between at least two of these coupled transmission lines to prevent any interchange of energy between the conjugately related lines.

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22,	for transmission line terminations for hybrid-type networks.
23,	for artificial lines adapted for use in hybrid systems.
24+,	for single channel coupling networks. 109, for branched circuits including a directional coupler so that wave energy passing in one direction along a first line will be propagated in the second line in only one direction from the coupling, and wave energy passing in the other direction along the first line will be propagated only in the opposite direction from the coupling.
169,	and 170+, for bridge-type filter networks.

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323,	Electricity: Power Supply or Regulation Systems, subclass 365 for bridge-type impedance systems.
336,	Inductor Devices, appropriate subclasses for the structure of transformers per se.
370,	Multiplex Communications, appropriate subclasses, particularly subclasses 276+ for a duplex system, subclass 308 for a resonant transfer system, and subclasses 498+ for combining or distributing information via time channels which may include a hybrid circuit.
379,	Telephonic Communications, subclasses 338+ for repeater systems including hybrid-type networks; and subclasses 402+ for telephone substation circuits including hybrid-type networks.
455,	Telecommunications, subclasses 7+ for radio repeaters including hybrid networks.

118	... Having lumped parameters or impedances:

	This subclass is indented under subclass 117. Subject matter having impedance elements which may be considered as concentrated at one point.

119	.... Using transformer coil:

	This subclass is indented under subclass 118. Subject matter wherein the impedance element consists of mutually coupled windings.

120	... Having hybrid ring junction:

	This subclass is indented under subclass 117. Subject matter wherein the hybrid transmission line forms a closed loop, there being a plurality of ports connected to the loop.

121	... Having hybrid-T (e.g., magic-T):

	This subclass is indented under subclass 117. Subject matter wherein the hybrid has four ports; energy being interchanged between the first port and two other ports, with no energy propagation from the fourth port, and the first and fourth ports being decoupled.

122	.... Using waveguide:

	This subclass is indented under subclass 121. Subject matter wherein the transmission line is of the type having an electric or magnetic field extending in the direction of propagation.

123	... Having coaxial element:

	This subclass is indented under subclass 117. Subject matter wherein the transmission is of the TEM type having an elongated center conductor and a surrounding outer conductor.

124	.. With impedance matching:

This subclass is indented under subclass 100. Systems wherein the interconnected or branched transmission lines present impedances at their junction to substantially eliminate the reflected wave energy caused by the junction or wherein one or more impedance elements are provided which are constructed or proportioned to substantially eliminate the reflected wave energy caused by the branched circuit coupling means.

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2+,	for branched circuit impedance matching which is automatically controlled.
22,	for single channel transmission line terminations involving impedance matching.
32+,	for single channel impedance matching coupling networks.

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324,	Electricity: Measuring and Testing, subclasses 600+ especially subclasses 612+ for the miscellaneous measurement and testing of impedance mismatch between circuits; and subclasses 140+ for systems and apparatus for the measurement of voltage, current, or power ratios which are indicative of impedance mismatch.
343,	Communications: Radio Wave Antennas, subclass 852 for antennas with a plural path coupling network with impedance matching.

125	... Including long line element:

	This subclass is indented under subclass 124. Subject matter wherein a circuit element having distributed parameters is used.

126	.... For providing frequency separation:

	This subclass is indented under subclass 125. Subject matter wherein the impedance matched branching network provides a different frequency or band of frequencies in each of the two or more transmission lines or in the plural outputs.

127	.... Using TEM lines:

	This subclass is indented under subclass 125. Subject matter wherein the transmission lines are the type having only transverse electromagnetic components as their primary mode of operation.

128	..... Stripline:

	This subclass is indented under subclass 127. Subject matter wherein the TEM lines are of the type having a planar center conductor and a planar ground plate.

129	... For providing frequency separation:

	This subclass is indented under subclass 124. Subject matter wherein the branched transmission lines provide a different frequency or band of frequencies in each of the two or more transmission lines.

130	... Using resistors only:

	This subclass is indented under subclass 124. Subject matter wherein the impedance matching elements consist solely of resistors.

131	... Using coupled windings:

	This subclass is indented under subclass 124. Subject matter wherein the impedance matching elements comprise inductively coupled coils (i.e., transformers and auto transformers).

132	.. For providing frequency separation:

	This subclass is indented under subclass 100. Subject matter wherein the interchange of wave energy provides a different frequency or band of frequencies in each of the two or more transmission lines or in the plural outputs.

133	... Utilizing electromechanical transducer:

	This subclass is indented under subclass 132. Subject matter wherein an electrical wave driven mechanical vibrator determines the frequency characteristic of the branched circuit.

134	... Utilizing long line element:

This subclass is indented under subclass 132. Subject matter wherein the transmission lines or coupling networks include an element having distributed parameters.

(1) Note. A long line element is a circuit element having distributed parameters, such as a resonator, or a waveguide. A long line element may be a part of a long line wave transmission device or used in a network with other circuit elements of the lumped parameter type, for example, as in the case of delay networks, impedance matching networks, and wave filters.

135	.... Including waveguide element:

This subclass is indented under subclass 134. Subject matter wherein the long line element is of the type having a magnetic or electrical component extending in the direction of propagation.

(1) Note. A waveguide is a transmission device designed to propagate electrical waves having an electric or magnetic field component extending in the direction of propagation. The waveguide may be a hollow dielectric or metal tube or a solid dielectric rod, the wave energy being propagated along the interior of the tube or rod and confined by the walls of the tube or rod.

136	.. Including long line element:

	This subclass is indented under subclass 100. Subject matter wherein the branched circuit includes a circuit element having distributed parameters.

137	... Using waveguide:

	This subclass is indented under subclass 136. Subject matter wherein the long line element is of the waveguide type.

12	TRANSMISSION LINE INDUCTIVE OR RADIATION INTERFERENCE REDUCTION SYSTEMS:

This subclass is indented under the class definition. Subject matter including a transmission line producing inductive or radiation interference or subject to such interference from an external source and means such as one or more filters, screens or compensating circuits, disposed along an appreciable length of the line for substantially reducing this interference.

(1) Note. Subclass 12 does not include mere echo or anti-singing systems. Such systems in a single channel system where classified in this class are classified with the first occurring (lowest numbered) subclass providing for any of the components used in the system.

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5,	for plural channel systems, which are balanced to prevent undesired radiation effects.
24+,	for networks which may be used to reduce undesired currents in a transmission line, and particularly subclasses 138+ for balanced circuits coupled to unbalanced circuits and subclasses 165+ for wave filters and for transmission lines connected to filters which block such undesired currents.
236+,	for long line transmission line structure which inherently reduce interference radiation effects and which involve no shielding structure or means in addition to the conductor arrangement or structure (e.g. co-axial lines), see especially subclasses 243+.

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174,	Electricity: Conductors and Insulators, subclasses 32+ and the subclasses specified in the notes thereto for structure and conductor arrangements for preventing or reducing the detrimental effects due to either self-inductance of a single conductor or mutual inductance between plural conductors, other than loaded lines or transmission lines defined as having long line characteristics.
178,	Telegraphy, subclass 45 for loaded lines with inductive or radiation reduction means, subclass 63, for cable or long line telegraph systems having means for eliminating "tailings" or having static compensation; and subclass 69 for telegraph line clearing and circuit maintenance systems having means for preventing the detrimental effects produced by induction from external or internal causes.
307,	Electrical Transmission or Interconnection Systems, subclasses 89+ for miscellaneous electrical systems having anti-induction means or means to prevent undesired coupling to other systems.
331,	Oscillators, subclass 67 for oscillator systems provided with an electromagnetic or electrostatic shield.
343,	Communications: Radio Wave Antennas, subclasses 841+ for antennas with an electrical shield; subclass 851 for antennas with a coupling network having a radiation suppressor; and subclass 905 for antennas combined with shielded transmission lines.
361,	Electricity: Electrical Systems Devices, subclasses 1+ for transmission lines with means to protect the connected lines from the effects of lightning and other high potential, and for networks for use in surge suppression circuits, see especially subclass 50 for systems with means to adjust for varying leakage currents; subclasses 82 and 84+ for systems for protecting balanced electrical systems (e.g., polyphase) for balanced current flowing therein; subclasses 88+ for voltage responsive systems; subclass 111 for transient responsive systems; and subclasses 177+ for high voltage dissipation systems (e.g., lightning arresters).
365,	Static Information Storage and Retrieval, subclass 198 for transmission lines used for reading and writing information.
379,	Telephonic Communications, subclass 398 for telephone systems having means for preventing the detrimental effects occasioned by induction from external or internal causes and subclasses 406.01-406.16 for echo-suppressing and/or anti-singing systems in plural channel systems.

13	RESONATOR-TYPE BREAKDOWN DISCHARGE SYSTEMS (E.G., T-R OR R-T SYSTEMS):

This subclass is indented under the class definition. Systems which include a resonant device and a space discharge structure positioned at a point of high potential on said resonant device, the space discharge structure breaking down in response to energy above a predetermined level in a transmission line connected to the resonant device to modify the effective electrical characteristics of the resonant device so as to block substantially the flow of any energy over the transmission line, free passage of energy occurring over the line when the energy fails to attain this predetermined level.

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2+,	for plural channel systems which include a resonator type breakdown discharge system for substantially blocking a channel where the discharge device is made conductive by a high energy level in the transmission line, and subclasses 100+ where the discharge device is made conductive by energy other than the energy in the transmission line.
2+,	14, 15, 16, 17+, and 81, for other systems within the class definition which reduce the amplitude of the wave energy but which do not involve the use of a resonator type breakdown discharge device.
262,	for transmission line elements and components which perform a switching or blocking function, other than resonator type breakdown discharge systems.

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313,	Electric Lamp and Discharge Devices, subclasses 567+ for miscellaneous gaseous discharge device structure, including lightning arresters, and subclasses 324 and 325 for lightning arresters of the spark or arc type which operate in the open air.
315,	Electric Lamp and Discharge Devices: Systems, subclasses 32 through 371for miscellaneous gaseous discharge systems and particularly subclass 39 for the structural combination of a discharge device and a resonant device, i.e., combined in an integral or nonseparable manner.
323,	Electricity: Power Supply or Regulation Systems, subclasses 304 through 317for self-regulating systems.
327,	Miscellaneous Active Electrical Nonlinear Devices, Circuits, and Systems, subclasses 365+ for miscellaneous gating circuits which utilize electron tubes.
361,	Electricity: Electrical Systems and Devices, subclasses 1+ for miscellaneous systems for protecting electrical apparatus by opening a circuit or making a shunt or short circuit when the current exceeds a predetermined value, see especially subclass 112 where the system includes electronic tubes, and subclasses 117+ for lightning arrester systems which include an arc discharge device.
455,	Telecommunications, subclasses 78+ for T-R or R-T radio systems.

14	AMPLITUDE COMPRESSION AND EXPANSION SYSTEMS (I.E., COMPANDERS):

This subclass is indented under the class definition. Networks including a non-linear device for decreasing the amplitude range of the signal applied to the device, and a nonlinear device connected to receive the wave having the decreased amplitude range for increasing or restoring the amplitude range of the signal, and long line transmission lines in combination with such networks.

(1) Note. This subclass provides for amplitude compression and expansion systems even though the system includes an active element such as a vacuum tube type amplifier. See (3) Note below.

(2) Note. This subclass does not include devices which merely shift the amplitude level up or down merely to control the peak amplitude without controlling the amplitude range. Neither does this subclass include the combination of a limiter or clipper and an amplifier which cuts off the higher amplitudes and then amplifies the remaining portion of the wave energy so that the output wave does not contain any variations in wave form above a certain amplitude level, and is not therefore a function of the input wave energy.

(3) Note. In the compressor portion of the compander, the input waves of smaller amplitudes may be increased in amplitude while the input waves of larger amplitude may be increased by a smaller ratio or decreased. All amplitudes of the wave may be decreased, the larger amplitudes being decreased to a smaller extent. The expander portion may operate in a similar manner except to increase the amplitude range.

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20,	for miscellaneous passive type wave shaping networks which modify the amplitude time characteristic of the signal transmitted therethrough.
81,	for the attenuator network in this class which reduces the energy of the signal passing therethrough.

SEE OR SEARCH CLASS:

178,	Telegraphy, subclass 45 , for loaded lines in combination with a compander.
327,	Miscellaneous Active Electrical Nonlinear Devices, Circuits, and Systems, subclasses 309+ for a miscellaneous limiter with an amplifying circuit.
330,	Amplifiers, subclasses 96 , 123 and 129+ for amplitude range compressors or expanders of the amplifier type where the input signal is applied to a control grid of an amplifier tube whose bias is controlled in accordance with the signal intensity to produce the necessary compression or expansion, and wherein the output signal is abstracted from the plate of the amplifier tube. Subclasses 143 and 144+ for compressors or expanders where a variable impedance element is included in the signal path and the variable impedance is controlled in accordance with the signal intensity. The combination of an amplitude compressor and expander (i.e., a compander) one or both being of the amplifier type is classified in this class, (333) subclass 14. However, where such combinations involve correction only of an amplifier condition and not a condition of the transmission line, classification is with amplifiers Class 330. Combinations of an amplifier and a limiter where the output more substantially conforms to the input wave form are classified in Class 330. See Class 250, subclass 27, above.
369,	Dynamic Information Storage or Retrieval, subclass 133 for phonograph recording and reproducing systems involving amplitude range compression and expansion.
370,	Multiplex Communications, subclass 202 for a multiplex system which includes an amplitude compression or expansion means.
381,	Electrical Audio Signal Processing Systems and Devices, subclass 106 for one-way audio signal transmission having amplitude compression/expansion.
704,	Data Processing: Speech Signal Processing, Linguistics, Language Translation, and Audio Compression/Decompression, subclasses 500+ for systems changing the frequency range of a band of audio signal frequencies, transmitting the energy at the changed range, and restoring the transmitted audio signal to its original frequency range.

15	PILOT LINE-CONTROLLED SYSTEMS:

This subclass is indented under the class definition. Systems including an auxiliary line so structurally related to a transmission line that a change in the transmission line characteristics caused by a change in an ambient condition, such as temperature or humidity, will be accompanied by a change in a parameter of the auxiliary line, and means controlled by this change in parameter to compensate for the change in transmission line characteristics.

SEE OR SEARCH THIS CLASS, SUBCLASS:

2+,	for plural channel systems including a pilot line.
16,	for systems utilizing a pilot current for purposes of control.

SEE OR SEARCH CLASS:

323,	Electricity: Power Supply or Regulation Systems, subclass 294 for impedance systems in general which are automatically controlled in response to a thermal condition.
330,	Amplifiers, subclass 52 , for amplifier systems having control means, wherein the control is exercised by a pilot signal. See the Class Definition of Class 330 for the line between this class (333) and Class 330 where pilot signals are involved.
379,	Telephonic Communications, subclasses 338+ for repeater systems (e.g. two way amplifier system) which utilize a pilot line to compensate for changes in the transmission characteristics of the main line.

16	PILOT CURRENT-CONTROLLED SYSTEMS:

This subclass is indented under the class definition. Systems including means for compensating for changes in the signal energy passing over a transmission line caused by changes in the line characteristics, wherein a control signal distinct from and in addition to the signal energy is also passed over the line to be influenced by the changes in line characteristics, the control signal being used to control the compensating means.

SEE OR SEARCH THIS CLASS, SUBCLASS:

2+,	for plural channel systems utilizing a pilot frequency.
15,	for systems utilizing for a pilot line for control purposes.
17.1+,	for systems for automatically compensating for changes in the characteristics of a transmission line where the carrier current of the transmitted energy is used to control the compensating means.

SEE OR SEARCH CLASS:

330,	Amplifiers, subclass 52 for amplifier systems having pilot signal control means. See Class 330, Class Definitions for the line between the two classes where such subject matter is involved.
379,	Telephonic Communications, subclasses 338+ for repeater systems (e.g., two way amplifier system) which may utilize a pilot current to compensate for changes in the transmission characteristics of the main line.

17.1	AUTOMATICALLY CONTROLLED SYSTEMS:

This subclass is indented under the class definition. Subject matter having means to sense a condition in the system and to modify a wave propagation characteristic of the system in accordance with the condition so sensed.

(1) Note. The automatic control must be of the wave propagation characteristic of a transmission line, system or network which would be classified in this class. Where the system or network includes a component or device which, per se, is not classified in the class, combined with a transmission line, system or network which causes classification of the subject matter in this class, and the automatic control is only with respect to such component or device which is classified, per se, in another class. Then the patent is not classified in this or the indented subclass, but is classified in subclass providing for the subject matter claimed. For example, a wave filter combined with an automatically operated current or voltage magnitude control means does not effect the wave propagation characteristic of the filter are classified in subclasses 165+ below.

SEE OR SEARCH THIS CLASS, SUBCLASS:

2+,	for plural channel systems including automatic control.
13,	for resonator type breakdown discharge systems which are automatically controlled.
14,	for amplitude compression and expansion systems including automatic control.
15,	for pilot line controlled systems involving automatic operation.
16,	for pilot current controlled systems including automatic operation.

SEE OR SEARCH CLASS:

307,	Electrical Transmission or Interconnection Systems, appropriate subclasses, especially subclasses 92+ , 97, 99, and 116 for miscellaneous electrical distribution systems with automatic control means.
323,	Electricity: Power Supply or Regulation Systems, subclasses 234 through 303for condition sensing regulators.
327,	Miscellaneous Active Electrical Nonlinear Devices, Circuits, and Systems, subclasses 509+ and 518+ for miscellaneous externally effected or control circuits.
331,	Oscillators, subclasses 1+ for oscillator systems utilizing a phase or frequency sensing means for automatically stabilizing the oscillator frequency subclass 183 for oscillator systems having means for automatically controlling or stabilizing the amplitude of the generated oscillations and subclass 186 for oscillator systems with a particular source of power or bias voltage of the automatically regulated type.
336,	Inductor Devices, particularly subclasses 30+ for inductor devices automatically adjustable in response to a condition.

17.2	. Limiting of amplitude:

This subclass is indented under subclass 17.1. Subject matter including means to limit the amplitude to a predetermined level.

SEE OR SEARCH THIS CLASS, SUBCLASS:

81,	for systems and networks that selectively lower the input signal level to a desired amount.

SEE OR SEARCH CLASS:

307,	Electrical Transmission or Interconnection Systems, subclasses 264 and 540+ for limiting the amplitude of pulses in nonlinear solid state circuits.

17.3	. Impedance matching:

This subclass is indented under subclass 17.1. Subject matter in which the condition sensed is utilized to control circuitry that performs an impedance matching function in the system.

SEE OR SEARCH THIS CLASS, SUBCLASS:

32+,	for impedance matching circuits of the nonautomatically controlled type.

SEE OR SEARCH CLASS:

455,	Telecommunications, subclasses 120+ for frequency tuning a transmitter to an antenna.

18	. With control of equalizer and/or delay network:

This subclass is indented under subclass 17.1. Systems and networks provided with automatically operated means to control an equalizer and delay network.

(1) Note. This subclass includes systems including an equalizer and/or a delay network which is automatically controlled in response to some condition in the system and also equalizers and/or delay networks which are provided with other automatic control means.

SEE OR SEARCH THIS CLASS, SUBCLASS:

12,	for automatic equalization and/or delay control networks utilized for preventing, suppressing or eliminating interference.
15,	for automatic equalization and/or delay control networks controlled by the signal derived from a pilot line.
16,	for automatic equalization and or delay control networks involving a pilot current control.
28,	for nonautomatic equalizers.
138+,	for nonautomatic delay networks.

SEE OR SEARCH CLASS:

323,	Electricity: Power Supply or Regulation Systems, subclasses 212 through 219for automatic phase control systems involving a single frequency.
363,	Electric Power Conversion Systems, subclasses 2+ , 9+ and 36 for plural conversion systems involving phase conversion; subclasses 148+ for phase conversion systems, per se; particularly subclass 149 for phase conversion systems involving automatic voltage magnitude or phase angle control.

19	DIFFERENTIATING OR INTEGRATING SYSTEMS:

This subclass is indented under the class definition. Passive networks for producing an output wave which is the time derivative or time integral of the input wave.

(1) Note. See the internal and external search notes under subclass 20 of this class for wave shaping systems which may involve differentiating and/or integrating networks.

SEE OR SEARCH THIS CLASS, SUBCLASS:

20,	for passive networks for shaping the output wave to other than the time derivative or time integral of the input wave. Also see (1) Note above.

SEE OR SEARCH CLASS:

318,	Electricity: Motive Power Systems, subclasses 609+ and 611+, particularly subclasses 621+ for position servomechanisms which include stabilizing control features such as integrating and differentiating networks; subclasses 141+ for generator fed motor systems having generator control including anti-hunt or rate of change response; subclass 702 for synchronous motor systems having anti-hunt or anti-damping control; subclass 448, for open loop automatic motor control systems involving anti-hunt control; and subclasses 456+ for systems responsive to the rate of change of a condition.
322,	Electricity: Single Generator Systems, subclass 19 for systems for automatically controlling the rate of change or hunting of a generator or its driving means.
323,	Electricity: Power Supply or Regulation Systems, subclasses 212 through 219for miscellaneous phase control networks which involve differentiating or integrating networks.
327,	Miscellaneous Active Electrical Nonlinear Devices, Circuits, and Systems, subclass 335 for miscellaneous differentiating circuits and subclasses 336+ for miscellaneous integrating circuits.
708,	Electrical Computers: Arithmetic Processing and Calculating, subclasses 822 and 823+ for calculators performing computations involving differentiation and integration, respectively.

20	WAVE-SHAPING:

This subclass is indented under the class definition. Passive networks for modifying an electrical wave passing therethrough so that the amplitude time characteristic of the output wave is different from that of the input wave and which have no function classified in other classes, and long line wave transmission systems in combination with a passive wave shaping network.

(1) Note. The networks are usually designed to modify or shape a single pulse and usually involve a delay network or equivalent delay means.

(2) Note. Included are long transmission lines in combination with a wave shaping network which is designed to restore the wave shape to a wave which has been distorted by transmission over the transmission line.

(3) Note. Excluded are mere limiter networks which shape the wave merely by cutting off the wave above a predetermined amplitude.

(4) Note. Many systems and networks inherently function to wave shape. Most of these systems are excluded as they include active elements, such as oscillation generators, amplifiers, detectors, etc. Where the network is primarily designed for a purpose other than wave shaping, such as controlling the magnitude of current in the circuit, the network is excluded even though the control of the current magnitude is effected by a means which also effects the wave shape of the element.

SEE OR SEARCH THIS CLASS, SUBCLASS:

1+,	for systems combining wave energy from different channels and/or separating wave energy into different channels.
14,	for amplitude range compression and expansion systems.
19,	for wave shaping networks producing a time derivative or time integral of the applied wave energy (i.e. differentiating or integrating networks).
28,	for networks modifying the attenuation or attenuation and phase characteristic with respect to frequency of the energy passing therethrough (i.e. equalizers).
81,	for attenuator networks.

SEE OR SEARCH CLASS:

84,	Music, subclasses 622+ , 626+, 659+, 671-677 and 692-711 for systems for the electrical production of complex waves in musical instruments.
178,	Telegraphy, subclasses 2+ , and particularly subclasses 63, 69 and 69.1 for telegraph systems involving combining and/or separating and/or shaping of electric waves.
307,	Electrical Transmission or Interconnection Systems, subclasses 106+ for waveform or wave shape determinative or pulse producing systems which are class appropriate. The networks and systems in Class 307 may involve long line elements, but ordinarily include also a specific source of wave energy or pulse producing means, such as a DC source and switching means.
324,	Electricity: Measuring and Testing, subclasses 76.12+ for electrical systems for the analysis of complex waves, and subclasses 76.39+ for electrical frequency measuring systems which involve wave analysis.
327,	Miscellaneous Active Electrical Nonlinear Devices, Circuits, and Systems, subclasses 100+ for miscellaneous converting, shaping, or generating circuits such as miscellaneous limiters and clock or pulse production circuits.
330,	Amplifiers, subclasses 53+ for amplifier systems combined with a long line element, where the amplifiers may correct for the distortions caused by the long line.
331,	Oscillators, subclasses 75+ for oscillator systems combined with an output circuit including a space discharge or unilaterally conductive device, which device may provide a wave distorting or shaping function.
332,	Modulators, appropriate subclasses for modulator systems which involve wave shaping.
340,	Communications: Electrical, subclasses 13.37 and 13.38 for selective electrical communication systems wherein the selective means is responsive to the amplitude of the signal.
363,	Electric Power Conversion Systems, appropriate subclasses for conversion systems which involve wave shaping, see subclasses 34+ for systems for converting AC to DC and then connecting the DC to AC, subclasses 39+ for conversion systems with means to introduce or eliminate frequency components, and subclasses 157+ for frequency conversion systems. The systems in Class 363 usually involve the use of alternating current which is repetitive and do not involve the shaping of a single pulse.
379,	Telephonic Communications, appropriate subclasses for telephone systems involving combining and/or separating and/or shaping of electric waves.

21R	WAVE MODE CONVERTERS:

This subclass is indented under the class definition. Wave transmission systems comprising means for changing guided waves having one field configuration to a different field configuration, the original and changed waves each having a longitudinal electric or magnetic field component.

(1) Note. This subclass includes means for changing a rectangular TE wave pattern to a circular TE wave pattern, e.g. for changing a plane polarized guided wave to a circularly polarized guided wave, or from one type of polarized wave to another.

SEE OR SEARCH THIS CLASS, SUBCLASS:

248+,

for mode filters or suppressors, and for wave guide junctions (e.g. rotary joints involving mode conversion and reconversion).

SEE OR SEARCH CLASS:

343,	Communications: Radio Wave Antennas, subclass 756 for antennas with a polarization converter; and subclasses 909+ for radio wave polarizers, per se.

21A	. Polarization converters

	This subclass has no definition.

22R	DISSIPATING TERMINATIONS FOR LONG LINES:

This subclass is indented under the class definition. Networks specialized for use with and designed for connection to the end of a long line transmission line and including a resistive component for dissipating the wave energy propagated along the line and presenting an essentially resistive impedance to the line, and the combination of long transmission lines with energy dissipating terminations.

(1) Note. Usually the impedance presented by the network is equal to the characteristic impedance of the line for which it is designed.

(2) Note. The termination classified here is usually more than a mere resistance element such as is classified in Class 338, Electrical Resistors. The termination includes some structure, such as a long line element or component, so that the device is not of general utility, but is limited to use with a transmission line. Long lines with mere resistance elements which would, per se, be classified in Class 338, are included in this subclass (22) when the resistance element is designed for use as a long line dissipating termination.

SEE OR SEARCH THIS CLASS, SUBCLASS:

23,	for networks simulating transmission lines (i.e. artificial lines) whose function is not essentially dissipating terminal energy.
32+,	for impedance matching networks whose function is coupling as opposed to termination.
81,	for attenuators, which dissipate only a portion of the wave energy applied thereto.

SEE OR SEARCH CLASS:

343,	Communications: Radio Wave, subclass 18 for radio wave absorption devices; subclasses 731+ for traveling wave type antennas which may involve a dissipating termination; and subclasses 739+ for antennas with a terminating resistance at open end.
361,	Electricity: Electrical Systems and Devices, subclasses 117+ for surge dissipators and lightning arresters.

	This subclass has no definition.

23	ARTIFICIAL LINES:

This subclass is indented under the class definition. Networks for simulating impedance characteristics of a smooth or loaded electrically long transmission line over a frequency range.

SEE OR SEARCH THIS CLASS, SUBCLASS:

22,	for dissipating terminations for long lines which usually have an impedance characteristic equal to the characteristic impedance of the line.
28,	for equalizing networks having impedance characteristics usually the inverse of electrically long transmission lines.
81,	for attenuators.

SEE OR SEARCH CLASS:

330,	Amplifiers, subclass 57 , for amplifiers utilizing artificial lines. (This also includes the "distributed amplifiers.")

24R	COUPLING NETWORKS:

This subclass is indented under the class definition. (a) Networks including significant reactive structure for effecting the transfer of oscillator energy from one circuit to another circuit and having attenuation and/or delay characteristics over a frequency range for attenuating and/or delaying in a predetermined manner, wave energy passing therethrough, and/or providing an impedance match between the network and at least one of the circuits; (b) smoothing type wave filters having shunt capacitance, or series inductance, or both usually designed to pass direct current and to reduce the effect of any undesired alternating or pulsating current, or to pass direct current and low frequency alternating current or pulsating current and to reduce the effect of any undesired higher frequency alternating or pulsating current, and (c) systems within the class definition including one or more of the networks defined in (a) or (b) above.

(1) Note. The coupling networks under the above definition usually include a shunt impedance common to the input and output circuits.

(2) Note. The systems included are single channel systems having coupling networks, and include for example echo suppression on a single channel where the echo would be due to an impedance mismatch, or the elimination of echo in a single channel system by using a delay line. Such systems are classified in the first indented subclass which provides for the network used in the system. See section I, subsection C, of the Class Definition.

(3) Note. Class 323, Electricity: Power Supply or Regulation Systems, is the miscellaneous class for systems for coupling a single source to a single load circuit using only transformers and/or impedances. Also, see (4) Note below.

(4) Note. Coupling networks using an electronic tube as a part of the network are not included in this or the indented subclass, but are classified in the appropriate class providing for the system. For examples, see the Search Class notes below.

(5) Note. See the Search Class notes below for a reference to the classification lines between coupling networks and antennas combined with such coupling networks.

SEE OR SEARCH THIS CLASS, SUBCLASS:

1+,	for plural channel systems involving coupling networks.
17+,	for automatically controlled systems involving coupling networks.
81,	for attenuators of the resistive type.
245+,	for transmission line joints within the class definition which do not modify the characteristics of the wave propagated therethrough or do not effect an impedance match between dissimilar impedance lines or networks.

SEE OR SEARCH CLASS:

178,	Telegraphy, appropriate subclasses for coupling networks in combination with code signaling systems or apparatus other than telephony. See subclass 64 for such systems for transmitting messages by induced currents utilizing an induction coil or transformer, and for such systems having an induction coil or transformer between sections of the main line.
307,	Electrical Transmission or Interconnection Systems, particularly subclasses 1+ for miscellaneous superimposed current systems involving coupling networks, and subclasses 11+ and 43+ for miscellaneous plural load or plural supply systems which include coupling networks.
323,	Electricity: Power Supply or Regulation Systems, see (3) Note, above. Class 323 provides for the miscellaneous transformer and impedance systems and includes structural combinations of different impedances which are electrically connected together.
323,	Electricity: Power Supply or Regulation Systems, for a coupling network using tubes to control the current and/or voltage magnitude and/or for phase control where there is a single input and output and at least a part of the input energy appears in the output circuit. (See the (4) Note above.)
327,	Miscellaneous Active Electrical Nonlinear Devices, Circuits, and Systems, subclasses 261+ for a delay system using tubes; subclasses 552+ for a filter using tubes; subclass 231 for a phase shifter using tubes where the input energy is applied to an input electrode (e.g., grid) of the tube to control a local source of energy (e.g., anode supply) connected to the output electrode of the tube. (See the (4) Note above.)
330,	Amplifiers, appropriate subclasses for various types of coupling networks involved in amplifier systems, subclass 116 for an amplifier system with means to couple a balanced line to an unbalanced line. (See the (4) Note above.)
331,	Oscillators, subclasses 74+ for oscillation generators combined with a particular output coupling network.
334,	Tuners, for tuners, per se. See also (4) Note above for tuners combined with other systems.
336,	Inductor Devices, appropriate subclasses for the structure of transformers and inductances of the passive type.
343,	Communications: Radio Wave Antennas, subclass 743 for high frequency loop type antennas with feed coupling at spaced points on the loop; subclass 771 for slot type antennas with wave guide coupling; subclasses 814, 816 and 820+ for balanced doublet type antennas with a coupling network, subclasses 850+ for antennas in general with a coupling network or impedance in the leadin; subclass 700, (11) Note, for the classification lines between coupling networks and antennas combined with such coupling networks (see the (5) Note above).
361,	Electricity: Electrical Systems and Devices, subclasses 600+ for miscellaneous combinations of different impedances which are not in circuit relationship (e.g., a variable condenser combined with a resistance with no electrical connection between them).
379,	Telephonic Communications, appropriate subclasses for telephone systems having coupling networks. If the system is limited to use with speech (other than by mere name), such as including a microphone or reproducer (e.g., loudspeaker) the system is classified in Class 381, see subclasses 338+ for repeaters utilizing hybrid coil systems.
455,	Telecommunications, subclasses 91+ for radio transmitters involving coupling networks and subclasses 130+ (particularly subclasses 338+) for radio receivers involving coupling networks.

24.1	. Nonreciprocal gyromagnetic type (e.g., directional phase shifters):

This subclass is indented under subclass 24. Networks which include gyromagnetic elements for effecting a nonreciprocal transfer of oscillatory energy from one circuit to another circuit.

(1) Note. Many of the patents in this generic subclass 24.1 are directional phase shifters, and relate to networks that shift the phase of energy passing through by different amounts depending on the direction of passage.

SEE OR SEARCH THIS CLASS, SUBCLASS:

1.1,	for a definition of the terms "gyromagnetic" and "nonreciprocal" and for plural channel nonreciprocal gyromagnetic systems.
138+,	for delay networks generally.
202+,	for waveguide filters generally.

SEE OR SEARCH CLASS:

324,	Electricity: Measuring and Testing, subclasses 300+ for nuclear or electronic induction measuring or testing devices.
330,	Amplifiers, subclasses 4 , 4.8 and 63 for amplifiers using gyromagnetic elements.
455,	Telecommunications, subclass 323 for mixers using gyromagnetic elements.

24.2	.. Nonreciprocal attenuators or isolators:

This subclass is indented under subclass 24.1. Networks wherein the attenuation in one direction of propagation through the network is substantially greater than in the opposite direction.

(1) Note. The attenuation in one direction may be substantially zero.

SEE OR SEARCH THIS CLASS, SUBCLASS:

81,	for attenuators generally.

24.3	.. Nonreciprocal polarization rotators:

This subclass is indented under subclass 24.1. Networks wherein the polarization of the electric vector of the wave energy propagated through the network is rotated in the same absolute sense for both directions of propagation.

(1) Note. Included in this subclass are the so-called anti-reciprocal or Faraday rotators.

SEE OR SEARCH THIS CLASS, SUBCLASS:

248+,

for rotators generally.

25	. Balanced to unbalanced circuits:

This subclass is indented under subclass 24. Networks including four terminals, the impedance across one pair of terminals being symmetrical and the impedance across another pair of these terminals being unsymmetrical with respect to a given potential plane (e.g., ground), these impedances being effective to convert symmetrical potential applied at the symmetrical pair of terminals to unsymmetrical potential at the other pair of terminals or to convert unsymmetrical potential applied at the unsymmetrical pair of terminals to symmetrical potential at the other pair of terminals, and systems under the class definition including a balanced to unbalanced circuit coupling.

SEE OR SEARCH THIS CLASS, SUBCLASS:

1+,	for plural channel systems, which involve coupling a balanced circuit to an unbalanced circuit or vice versa.
12,	for systems for reducing inductive or radiation interference and which include coupling between balanced and unbalanced circuits.

SEE OR SEARCH CLASS:

323,	Electricity: Power Supply or Regulation Systems, subclasses 212 through 219for phase control systems with means to introduce delay into a part of the system, and including such systems using reactive impedances and transformer systems to obtain a phase shift (e.g., a 1805 shift) and which are designed for use at a single frequency.
329,	Demodulators, appropriate subclasses for demodulators having inputs or outputs which are balanced or unbalanced.
330,	Amplifiers, subclasses 275 and 301 for transistor amplifiers with balanced-to-unbalanced coupling and vice versa, subclass 116 for amplifier systems having balanced-to-balanced coupling, and subclass 117 for amplifier systems having unbalanced-to-balanced coupling.
343,	Communications: Radio Wave Antennas, subclass 821 for balanced doublet type antennas with a balanced to unbalanced coupling network; and subclass 859 for antennas in general with a balanced to unbalanced coupling network.
363,	Electric Power Conversion Systems, subclasses 2+ , 9+, 36, and 148+ for systems converting energy from one number of phases to a different number of phases.

26	.. Having long line elements:

This subclass is indented under subclass 25. Balanced to unbalanced circuit coupling networks and systems where the coupling network includes a long line element.

SEE OR SEARCH THIS CLASS, SUBCLASS:

236+,	for long lines.
245+,	for long line elements.

27	. Interlinking long line:

This subclass is indented under subclass 24. Coupling systems having a long line with a coupling network at each opposed ends of the long line.

(1) Note. Where the long line is merely a part of a coupling network, and does not link two different coupling networks together, classification is not in this subclass. See subclasses 156+ for this type of delay network, subclasses 50+ for this type of impedance matching network, 202+ for this type of wave filter.

(2) Note. In this subclass are systems having two coupling networks with a long transmission line connected to transmit energy from one network to the other. These systems approach a complete system. For example, a 70 ohm source connected by a network to a 300 ohm line which is coupled by a network to a 150 ohm receiver. At each point of connection there would be a coupling network.

SEE OR SEARCH THIS CLASS, SUBCLASS:

50+,	see (1) Note above.
156+,	see (1) Note above.
202+,	see (1) Note above.
236+,	for long lines, per se.

SEE OR SEARCH CLASS:

178,	Telegraphy, appropriate subclasses where the system is limited to code signaling other than telephony.
330,	Amplifiers, subclasses 53+ for amplifier systems combined with long lines or long line elements wherein such means furnish a coupling means for the amplifier.
379,	Telephonic Communications, subclasses 90+ for composite telephone systems (e.g., combined power and telephone circuit) and subclasses 338+ for two telephone lines with two-way repeaters at spaced points along the line.
381,	Electrical Audio Signal Processing Systems and Devices, subclasses 82+ for public address and similar systems (e.g., a microphone and a line, or a line and a reproducer such as a loudspeaker or a microphone, a line and a reproducer).

28R	. Equalizers:

This subclass is indented under subclass 24. Networks with attenuation or attenuation and phase distortion characteristics which vary over a frequency range for use in a wave transmission system for modifying the attenuation or attenuation and phase characteristics of the wave energy as a function of frequency, and systems within the class definition which include such networks.

(1) Note. Equalizer networks are used to reduce the attenuation or attenuation and phase distortion characteristics which the wave energy in a long line transmission system would have in the absence of the network. The network may be used for predistorting so that the distorting effect of the long line will be corrected.

(2) Note. A filter is distinguished from an equalizer in that a filter is intended and designed to transmit a frequency or one or more bands of frequencies without modification while undesired frequencies are attenuated to a low value so that the desired frequency or frequencies are transmitted by the filter and the undesired frequencies are substantially blocked, while the equalizer has the function of changing the relative amplitudes of the waves of different frequency over the range of frequencies transmitted by the equalizer.

(3) Note. Included are tone control networks which involve only passive elements and which vary the attenuation or attenuation and phase distortion characteristics over a range of frequencies. Included are such networks as are used for "bass boosters", "treble boosters", "treble cut systems", etc.

SEE OR SEARCH THIS CLASS, SUBCLASS:

18,	for this subject matter where the equalizer is provided with automatic control means.
20,	for wave shaping systems.
81,	for attenuator networks within the class definition composed entirely of resistive elements.
138+,	for phase control or delay networks, per se.

SEE OR SEARCH CLASS:

323,	Electricity: Power Supply or Regulation Systems, appropriate subclasses for miscellaneous impedance and transformer systems, and for phase control systems.
330,	Amplifiers, appropriate subclasses, particularly subclasses 109 , 120, 122, 154, 157+, 185+, 192+, and 304, for amplifier systems combined with an equalizer network.
332,	Modulators, subclass 107 for distortion control in pulse modulators, subclasses 123+ for distortion control in frequency modulators, subclasses 144+ for distortion control in phase modulators, and subclasses 159+ for distortion control in amplitude modulators.
381,	Electrical Audio Signal Processing Systems and Devices, subclasses 98+ for audio signal processing devices and systems having frequency control.
455,	Telecommunications, subclass 267 for radio receivers with tone control networks.

28T	.. Audio tone control

	This subclass has no definition.

138	. Delay lines including a lumped parameter:

This subclass is indented under subclass 24. Subject matter for retarding wave energy a predetermined time over a range of frequencies and systems within the class definition which include such networks and wherein one of the network parameters may be considered as concentrated at one point.

(1) Note. See the class definition for the definition of "lumped parameters".

(2) Note. The time period may be constant over the range of frequencies or proportional to the frequency (e.g., the time of delay may be greater for the higher frequency).

(3) Note. This subclass does not contain pulse delay systems utilizing active elements.

SEE OR SEARCH THIS CLASS, SUBCLASS:

18,	for automatically controlled delay networks.
19,	for differentiating or integrating systems involving delay networks.
20,	for wave synthesis and shaping systems involving delay networks.
28,	for combined attenuation and phase control networks, per se.

SEE OR SEARCH CLASS:

178,	Telegraphy, particularly subclass 17.5 for transmitter for storing or delaying messages or code signals; subclasses 45+ for wave transmission lines with inductive loading means to effect changes in the delay characteristics of the transmission lines; subclass 63 for phase or delay control means applied to high capacity transmission line systems; and subclass 69 for line-clearing and circuit maintenance systems which include distortion and phase correction means.
307,	Electrical Transmission or Interconnection Systems, appropriate subclasses for the miscellaneous phase control systems similar to these in Class 323 but having plural source circuits and/or plural load circuits.
323,	Electricity: Power Supply or Regulation Systems, subclasses 212 through 219for devices for adjusting or maintaining the phase angle between the current and the voltage of an electric wave of a single frequency, or the phase angle between the current or voltage of a single frequency with respect to a standard or with respect to the current or voltage of another circuit wherein there is a single input source and a single output load and wherein the phase shift is produced by the device acting on the original electrical energy and not due to any interposed signal controlled transducer.
324,	Electricity: Measuring and Testing, subclasses 76.77+ for phase indicators.
327,	Miscellaneous Active Electrical Nonlinear Devices, Circuits, and Systems, subclasses 261+ for miscellaneous circuits which may include an electron discharge device or transistor and provide specific delay in producing an output waveform. see (3) Note above.
329,	Demodulators, subclasses 315+ for frequency demodulators and subclasses 345+ for phase demodulators.
330,	Amplifiers, appropriate subclasses for amplifiers combined with phase shifting networks and for phase inverter systems involving active elements having an amplifier function appropriate subclasses for phase compensation in amplifier systems. Also see (3) Note above.
331,	Oscillators, appropriate subclasses for oscillation generators utilizing time delay networks, particularly subclass 82 for beam tube oscillators of the traveling wave type; and subclasses 135+ for phase shift oscillators, indented subclass 137 providing for such oscillators with a phase shift network of the RC ladder type.
332,	Modulators, subclasses 144+ for phase modulation systems.
336,	Inductor Devices, appropriate subclasses for the structure of inductive reactors.
343,	Communications: Radio Wave Antennas, subclass 744 for high frequency loop-type antennas with series reactance in the loop; subclasses 749+ for antennas with lumped reactance for loading the antenna; and subclass 778 for plural waveguide-type antennas with phasing.
361,	Electricity: Electrical Systems and Devices, subclasses 271+ for capacitor structure.
363,	Electric Power Conversion Systems, subclasses 2 , 9, 148, and indented subclasses for systems for transforming electrical energy having one number of phases to electrical energy having another number of phases.
379,	Telephonic Communications, subclasses 398 and 415 for phase modifying means applied to anti-inductive systems.

139	.. Variable parameter:

	This subclass is indented under subclass 138. Subject matter including at least one variable parameter for delay adjustment.

140	.. Physical structure:

This subclass is indented under subclass 138. Delay lines subject matter wherein the geometry of individual parameters or the physical distribution of elements is critical to obtaining the desired delay.

(1) Note. Included here would be inductive parameters having a specific core structure and/or winding geometry.

141	. Delay lines including elastic bulk wave propagation means:

This subclass is indented under subclass 24. Subject matter for retarding wave energy a predetermined time over a range of frequencies and systems within the class definition which include such networks wherein structure is provided for converting electrical wave energy to bulk wave mechanical energy, and for transmitting the bulk wave mechanical energy for reconversion to electrical wave energy.

(1) Note. The time period may be constant over the range of frequencies or proportional to the frequency (e.g., the time of delay may be greater for the higher frequency).

(2) Note. The delay is due to the lower propagation velocity of waves in the mechanical wave transmission path.

(3) Note. Included as mechanical wave transmission devices in this subclass are such devices as fluid columns, bars, rods, and plates.

(4) Note. By elastic bulk wave propagation is meant energy transmitted through the interior of an elastic wave propagation medium.

SEE OR SEARCH THIS CLASS, SUBCLASS:

186+,

for electromechanical filters employing bulk mode resonators.

SEE OR SEARCH CLASS:

74,	Machine Element or Mechanism, appropriate subclasses, especially subclass 1 for mechanical systems of linkages to shift the phase of a wave.
310,	Electrical Generator or Motor Structure, subclass 313 for piezoelectric surface acoustic wave devices; subclasses 334+ for various acoustic wave devices which use piezoelectric effects; and subclass 26 for miscellaneous magnetostrictive devices, per se.
318,	Electricity: Motive Power Systems, subclass 116 for piezoelectric motors; and subclass 118 for magnetostrictive motors.
322,	Electricity: Single Generator Systems, subclass 3 for magnetostrictive generator systems.
343,	Communications: Radio Wave Antennas, subclasses 5+ for radar and other reflected wave radio systems used to measure distance and which use delay networks, see especially subclasses 9, 10+, and 12+.
367,	Communications, Electrical: Acoustic Wave Systems and Devices, subclass 141 for underwater vibration transducers.
381,	Electrical Audio Signal Processing Systems and Devices, subclasses 150+ for telephone transmitters and receivers using magnetostrictive or piezoelectric effects.

142	.. Multipath propagation:

This subclass is indented under subclass 141. Subject matter wherein the initial direction of mechanical wave energy is changed.

(1) Note. This subclass includes devices wherein changes in propagation direction result from reflection, diffraction, refraction, or mode conversion.

143	... Spurious signal reduction:

This subclass is indented under subclass 142. Subject matter including means to reduce undesired signal generation.

(1) Note. Spurious signals may be generated by reflection, diffraction, refraction, or multiple mode generation.

144	.. Variable delay:

This subclass is indented under subclass 141. Subject matter wherein the effective length of the structure for transmitting mechanical waves may be varied to provide a variable delay.

(1) Note. Included in this subclass are devices wherein the propagation velocity within the structure for transmitting is a function of externally applied magnetic or electric fields, control voltages, radiation, or mechanical forces.

145	.. Nonuniform propagation path:

	This subclass is indented under subclass 141. Subject matter in which the structure for transmitting mechanical waves is tapered, stepped, or includes a hollow, composite, anisotropic, or nonhomogeneous propagation path.

146	.. Helical propagation path:

	This subclass is indented under subclass 141. Subject matter wherein the structure for transmitting mechanical waves includes a helical propagation path.

147	.. Propagation path has significant chemical or physical properties:

This subclass is indented under subclass 141. Subject matter wherein the material of the structure for transmitting mechanical waves significantly affects the delay characteristic.

(1) Note. The material, as a result if it is crystalline structure or of its composition, may provide low losses, low scattering, low dispersion, controlled dispersion, increased power handling capabilities, or temperature stability.

(2) Note. Included in this subclass are devices wherein the structure for transmitting mechanical waves is polarized, semiconductive, gyromagnetic, ferroelectric, superconductive, magnetoelastic, or is capable of magnetostatic wave propagation.

148	.. Including magnetostrictive transducers:

This subclass is indented under subclass 141. Subject matter wherein the conversion of electrical to mechanical energy or the conversion of mechanical to electrical energy is dependent on the magnetostrictive effect.

(1) Note. Magnetostrictive effect may be defined as the change in dimensions of a body when subjected to a magnetic field.

149	.. Significant transducer structure:

	This subclass is indented under subclass 141. Subject matter not classifiable in other subclasses indented thereunder where the transducers used for electromechanical conversion are structured or dimensioned to provide high efficiency conversion, impedance matching, mode conversion, shock resistance, or nonreflective properties.

150	. Delay lines including elastic surface wave propagation means:

This subclass is indented under subclass 24. Subject matter wherein structure is provided for converting electric waves to surface acoustic waves, transmitting the surface acoustic waves to a means for reconverting the acoustic waves to electrical waves.

(1) Note. This subclass is limited to devices where significant acoustic wave transmission is along the free surface of the transmission media.

(2) Note. The delay is due to the lower velocity of the waves along the free surface of the transmission means. No significant wave transmission is realized through the interior of the transmission.

(3) Note. The transmission media may comprise either flat or curved surfaces of a piezoelectric medium or a nonpiezoelectric medium having a surface coating of piezoelectric material.

SEE OR SEARCH THIS CLASS, SUBCLASS:

193+,

for filters employing surface acoustic waves.

151	.. Spurious signal or mode cancellation means:

This subclass is indented under subclass 150. Subject matter including structure to reduce the effects of spurious mechanical or electric wave signals or modes on the output signal of the delay line.

(1) Note. Spurious modes or signals may result from reflections of elastic surface waves, undesired conversion of surface wave modes to bulk wave modes, nonlinearity of the means for transmitting surface waves, or from undesired capacitive coupling.

(2) Note. The mode cancellation means may include acoustic absorbers, shielding electrodes, obstacles in the surface acoustic wave path, or surface wave propagation substrates having anisotropic propagation properties.

152	.. Variable delay:

This subclass is indented under subclass 150. Subject matter including means for varying the delay.

(1) Note. Delay variation may be achieved by mechanical translation of the input and output transducers used for electromechanical conversion or by including surface wave propagation substrates whose delay properties are altered by incident radiation, electron bombardment, or by the application of external field, forces, or control voltages.

(2) Note. The substrate material may include materials or coatings which are both semiconductive and piezoelectric, are both photosensitive and piezoelectric, or undergo significant dimensional changes or deformation as a function of externally applied heat or mechanical stress.

153	.. Including discontinuities within propagation means:

This subclass is indented under subclass 150. Subject matter wherein abrupt modifications are included in the elastic surface wave path so as to alter the delay or transmission characteristics of the path.

(1) Note. Such discontinuities may serve as reflectors, deflectors, diffractors, phase modifiers, or mode converters.

(2) Note. Transducers distributed along the wave transmission path to provide signal tapping functions (rather than wave perturbation) are not included here.

154	.. Significant transmitting or receiving transducer structure:

This subclass is indented under subclass 150. Subject matter wherein the transducers required for electromechanical wave conversion have structural attributes, relative orientation, spacing, or other structural organization critical with respect to contributing to desired wave delay or wave transmission characteristics.

SEE OR SEARCH THIS CLASS, SUBCLASS:

151,	for delay lines of the elastic surface wave type which include transducer structures providing spurious signal or mode cancellation functions.

155	.. Temperature stabilization or compensation:

	This subclass is indented under subclass 150. Subject matter wherein the materials or structural elements included in the delay lines reduce the delay time variations caused by ambient temperature change.

156	. Delay lines including long line elements:

This subclass is indented under subclass 24. Subject matter having distributed parameters and including significant structure for retarding wave energy a predetermined period of time over a range of frequencies and systems within the class definition which include such networks.

(1) Note. The time period may be constant over the range of frequencies or proportional to the frequency (e.g., the time of delay may be greater for the higher frequency).

SEE OR SEARCH THIS CLASS, SUBCLASS:

138,	for delay structures wherein the wave energy to be retarded propagates along line elements which include both distributed and lumped elements.
202+,	for wave filters including long line elements.
236+,	for long lines.
245+,	for long line elements and components.

SEE OR SEARCH CLASS:

343,	Communications: Radio Wave Antennas, subclass 778 for plural waveguide-type antennas with phasing.

157	.. Waveguide:

This subclass is indented under subclass 156. Subject matter wherein the structure for retarding energy propagates electrical waves having an electric or magnetic field component extending in the direction of propagation.

(1) Note. The waveguide may be a hollow dielectric or metal tube or a solid dielectric rod, the wave energy being propagated along the interior of the tube or rod and confined or bounded by the tube or rod.

158	... Including ferrite means:

This subclass is indented under subclass 157. Subject matter including ferrite within the waveguide.

(1) Note. The ferrite is usually biased by a fixed or variable external magnetic field so as to determine the magnitude of wave retardation.

159	... Having mechanically movable delay control means:

	This subclass is indented under subclass 157. Subject matter wherein the magnitude of wave retardation is adjusted by a movable dielectric or conductive member within or proximate to the waveguide.

160	.. Coaxial line:

	This subclass is indented under subclass 156. Subject matter wherein the structure for retarding wave energy is a transmission line in which one conductor surrounds the other, the two having a common longitudinal axis.

161	.. Planar line structure (e.g., stripline):

This subclass is indented under subclass 156. Subject matter wherein the structure for retarding wave energy is a transmission line including two or more spaced planar conductors.

(1) Note. The planar line structure for classification here may be of the stripline type, the microstrip type, or the slot line type.

162	.. Helical line structures and lines developed from a helical structure:

	This subclass is indented under subclass 156. Subject matter wherein the structure for retarding wave energy is a transmission line including at least one conductor having a helical configuration or a configuration developed from a helix.

163	... Having plural concentric helices:

	This subclass is indented under subclass 162. Subject matter wherein the structure for retarding wave energy is a transmission line including two or more concentric helical conductors.

164	.. Control of delay with semiconductive means:

This subclass is indented under subclass 156. Subject matter wherein the conductivity state of a semiconductive means associated with the delay line controls the magnitude of wave retardation.

(1) Note. The semiconductive means may include switching diodes, varactor diodes, or bulk effect semiconductors.

32	. With impedance matching:

This subclass is indented under subclass 24. Coupling networks which include one or more impedance elements constructed or proportioned to substantially eliminate the reflected wave energy between the network and at least one of the connected circuits caused by impedance differences; impedance matching networks, per se; and systems within the class definition which include such networks.

(1) Note. The particular construction or proportioning producing the impedance match should be claimed for classification in this subclass.

(2) Note. The impedance need only to be matched to pass the energy or frequency band of energy desired.

SEE OR SEARCH THIS CLASS, SUBCLASS:

8+,	for branched plural channel systems having impedance matching.
17+,	for systems wherein the impedance match is automatically controlled.
22,	for line terminations involving impedance matching.
81,	for attenuators having means for compensating for changes in terminal impedance caused by adjustment of the attenuator so as to match the impedances of the attenuator to the connected input and/or output circuit.
236+,	for long lines wherein reflected wave energy arising from the line structure is compensated.

SEE OR SEARCH CLASS:

324,	Electricity: Measuring and Testing, subclasses 600+ , especially subclasses 612+ for the miscellaneous measurement and testing of impedance mismatch between circuits, and subclass 140+, for systems and apparatus for the measurement of voltage, current or power ratios which are indicative of impedance mismatch.
343,	Communications: Radio Wave Antennas, subclass 822 for balanced doublet type antennas with an impedance matching coupling network; and subclasses 860+ for antennas in general with an impedance matching coupling network.

33	.. Having long line elements:

This subclass is indented under subclass 32. Impedance matching networks and systems including a long line element.

SEE OR SEARCH THIS CLASS, SUBCLASS:

236+,	for long lines.
245+,	for long line elements.

SEE OR SEARCH CLASS:

343,	Communications: Radio Wave Antennas, subclass 862 for antennas with an impedance matching coupling network including a long line element.

This subclass is indented under subclass 33. Impedance matching networks and systems wherein the long line element lies along the path of wave propagation through the network and has a physical dimension progressively increasing or decreasing along the path of propagation to result in a corresponding change in electrical parameters of the long line element.

SEE OR SEARCH CLASS:

343,	Communications: Radio Wave Antennas, subclass 863 for antennas with an impedance matching coupling network including a tapered long line element.

35	... Quarter-wave transformer type:

This subclass is indented under subclass 33. Impedance matching networks and systems wherein the component having distributed electrical parameters lies along the path of wave propagation through the network and is an odd integral number of quarter-wave lengths long.

SEE OR SEARCH CLASS:

343,	Communications: Radio Wave Antennas, subclass 864 for antennas with an impedance matching coupling network including a long line element of the quarter-wave transformer type.

165	. Frequency or time domain filters and delay lines utilizing charge transfer devices:

This subclass is indented under subclass 24. Subject matter for filtering or delaying wave energy wherein components of signals to be filtered or delayed are sensed, charge samples corresponding to the magnitude and/or phase of the signals are developed, the charges are sequentially transferred at a predetermined rate, and the charges are eventually sampled or sensed to develop filtered and/or delayed output signals.

166	. Time domain filters:

	This subclass is indented under subclass 24. Subject matter for filtering wave energy utilizing a tapped delay line wherein a required impulse response is synthesized by weighting and/or summing signals derived at the tap points.

167	. Frequency domain filters utilizing only lumped parameters:

This subclass is indented under subclass 24. Subject matter having only parameters which may be considered as concentrated at one point and permitting free transmission of electric waves of a single frequency or band of frequencies (which may include zero frequency) while attenuating substantially electric waves having other frequencies, or attenuating substantially electric waves of a single frequency or band of frequencies (which may include zero frequency) while permitting free transmission of electric waves having other frequencies, and systems within the class definition which include such networks.

(1) Note. Tuners, which are closely analogous to the wave filters in this class, are classified in Class 334, Tuners. The tuners usually found in Class 334 consist of a lumped inductance and capacitance element together with structure means to vary either or both elements in order to change the mean resonant frequency of the tuner. The tuners in Class 334 may include one or more long line elements in addition to a lumped inductance or capacitance element, or the tuner may consist of a distributed parameter type tuning unit which is adjusted in discrete, distinct steps. Two or more distributed parameter type tuner units which are of the continuously variable type and which are ganged together mechanically and/or electrically so as to have their mean resonant frequency adjusted in unison are properly classified in Class 334. Where only the bandwidth of the filter is varied without varying the mean resonant frequency, classification is in this class (333).

(2) Note. Filters combined with circuits having other functions classified in other classes are excluded and will be bound in other classes. See the classes referred to under "Search Class" below. Note the exception in the case of a mere current and or voltage control network combined with a filter in (4) Note.

(3) Note. Filters which include an active element are excluded. See Class 327, particularly subclasses 552+ where the active element is an electron tube or a transistor. Note that Class 327 includes some transversal filters.

(4) Note. Filters in combination with means merely to control the magnitude of the current and/or voltage in the network are included in this and the indented subclasses.

SEE OR SEARCH THIS CLASS, SUBCLASS:

1+,	for plural channel systems which include filters and for filters with plural input and/or output terminals.
19,	for differentiating or integrating networks which are analogous to wave filters.
20,	for wave shaping networks which are analogous to wave filters and which may include wave filters.
28,	for equalizing networks which are analogous to wave filters.
100+,	where the filter includes branching means (e.g., a single input with plural outputs).
124+,	for resonant filter networks for matching the impedance in branched circuits, and branched circuits with line sections analogous to wave filters for impedance matching purposes.
157+,	for delay networks which are analogous to wave filters.
202+,	for long lines having frequency discriminating properties.
219+,	for resonators including those with tuning means.

SEE OR SEARCH CLASS:

74,	Machine Element or Mechanism, subclass 1 for mechanical wave filters for transmitting mechanical waves of a particular frequency or band of frequencies.
84,	Music, subclasses 1.19+ , 621, 622, 699+ or 736 for electrical systems used in musical instruments to produce musical tones which include wave filters or tuners.
178,	Telegraphy, subclasses 2+ for telegraph systems involving wave filters; and particularly subclass 47 and indented subclasses for harmonic or reed type selective systems; subclass 49 for superposed current systems with frequency selection means.
181,	Acoustics, subclasses 175+ for sound filters.
307,	Electrical Transmission or Interconnection Systems, particularly subclass 105 for electrical distribution systems including wave filters and subclass 132 for circuit interrupting systems having filters to eliminate the higher frequency components.
322,	Electricity: Single Generator Systems, subclass 58 for generator controls with means for suppressing or minimizing undesired frequencies.
323,	Electricity: Power Supply or Regulation Systems, note that Class 323 provides for "filters" which control only the voltage and/or current magnitude. If the circuit which performs the filtering action is arranged only to "buck out" or balance the undesired components, classification is in Class 323.
327,	Miscellaneous Active Electrical Nonlinear Devices, Circuits, and Systems, particularly subclasses 552+ for unwanted signal suppression by an active filter which may utilize a transistor or an electron tube.
329,	Demodulators, appropriate subclasses for a demodulator which includes tuning or filtering.
330,	Amplifiers, subclasses 302+ for transistor amplifiers with frequency responsive means; subclass 86 for amplifiers having an automatically variable impedance in the feedback path; subclass 94 for amplifiers having a frequency responsive means in a cathode feedback path; subclass 109 for amplifiers with frequency responsive means in the feedback path; subclass 143 for amplifiers with a thermal impedance in the signal path which may be automatically variable; subclasses 144+ for amplifiers having an automatically variable impedance in the signal path including such subject matter involving a variable reactance for automatically tunable or selective circuits; subclass 154 for cascaded amplifiers including a resonant circuit; subclass 155 for amplifier circuits including means for unicontrol of the coupling circuits; and subclasses 157+ and 192+ for amplifier systems with significant interstage, input and output coupling which may include wave filters.
331,	Oscillators, appropriate subclasses, particularly subclasses 43 , 76, 77, 110, and 138+ for oscillators utilizing a wave filter as an element thereof.
332,	Modulators, appropriate subclasses for modulators involving wave filters.
340,	Communications: Electrical, subclasses 13.2 through 13.36for selective communication systems which are frequency responsive.
343,	Communications: Radio Wave Antennas, subclass 722 for antennas with a lumped reactance filter in the active antenna; and subclasses 745+ for antennas with a variable reactance for tuning the antenna.
363,	Electric Power Conversion Systems, subclasses 39+ for conversion systems in combination with a filter.
370,	Multiplex Communications, appropriate subclasses, particularly subclasses 488 and 497 for a multiplex system which includes connecting filters.
379,	Telephonic Communications, appropriate subclasses for telephone systems involving wave filters; and particularly subclass 2 and indented subclasses for composite systems utilizing wave filters; and subclasses 78, 79, 80, and 174 for anti-inductive systems and devices with wave discriminating properties.
381,	Electrical Audio Signal Processing Systems and Devices, subclasses 98+ for audio signal processing devices and systems having frequency control.
455,	Telecommunications, subclasses 91+ for transmitters involving wave filters; and subclasses 150.1+ and 296+ (especially subclass 307) for radio receivers with filters or tuners.

168	.. Including recurrent sections:

This subclass is indented under subclass 167. Subject matter wherein similar or equivalent elements or groups of elements are cascaded.

(1) Note. Examples of filters classified here are ladder network or reiterations of "T" or "pi" networks whose formats are topographically similar but whose parameters may not be equal in every reiteration. Examples of such filters included are:

Image 1 for class 333 subclass 168

Image 2 for class 333 subclass 168

169	.. Wheatstone or lattice type:

This subclass is indented under subclass 167. Subject matter having four impedance branches connected in series to form a closed circuit, two nonadjacent junction points serving as input terminals while the remaining two junction points serve as output terminals.

(1) Note. Two of the impedance branches may be formed by a transformer winding having a mid-tap, the mid-tap forming one of the input or output terminals, and the other winding of the transformer forming the output or input connecting means. See Fig. 4 below.

(2) Note. Included are for example:

Image 1 for class 333 subclass 169

Image 2 for class 333 subclass 169

Image 3 for class 333 subclass 169

Image 4 for class 333 subclass 169

SEE OR SEARCH THIS CLASS, SUBCLASS:

117+,	for hybrid-type networks used in branched circuits.
133+,	for similar networks which include electromechanical transducer elements.

SEE OR SEARCH CLASS:

236,	Automatic Temperature and Humidity Regulation, subclasses 69+ , 74, 78, and 91 for temperature regulating systems which include impedance bridge networks as the control means.
318,	Electricity: Motive Power Systems, subclass 294 for motor reversing systems wherein the armature current reversal means includes an impedance bridge network; and subclass 535 for motor field circuit control systems which include an impedance bridge network; and subclasses 663+ for position servomechanisms which may include a bridge in the error detector circuit.
322,	Electricity: Single Generator Systems, subclass 77 for single generator systems where the generator field circuit is controlled by means of an impedance bridge network.
323,	Electricity: Power Supply or Regulation Systems, subclass 365 for voltage magnitude control systems involving Wheatstone bridge arrangements.
324,	Electricity: Measuring and Testing, appropriate subclasses, especially subclasses 98+ and 101+ for electric measuring and testing systems using impedance bridge arrangements.
330,	Amplifiers, subclass 146 for amplifier systems having an amplifier in one arm of a bridge; and subclass 175 for amplifier systems having a lattice or Wheatstone bridge network in the signal coupling means.
331,	Oscillators, subclasses 110 and 138+ for bridge type oscillation generation systems in general.
332,	Modulators, subclass 172 for amplitude modulating systems of the bridge type having conjugate input and output.
363,	Electric Power Conversion Systems, subclasses 148+ for phase conversions arranged as a bridge.

170	.. Bridge type:

This subclass is indented under subclass 167. Subject matter having an impedance path containing a plurality of filter impedance units connected in series relation between an input and an output terminal, the filter also having a shunt connection containing an impedance connected to the junction of the series filter impedance units and to the other side of the line between the input and output terminals, an impedance path being connected to different ones of the series impedance units at points other than the junction between the units.

(1) Note. The last named impedance path is therefore in parallel with at least a portion of the series connected filter impedance units in the input circuit and the output circuit. The last named impedance path may include an inductive coupling.

(2) Note. Examples of filter networks included and excluded are:

Included

Included

Inductively Coupled

Inductively Coupled

Excluded

Excluded

SEE OR SEARCH CLASS:

331,	Oscillators, subclass 142 in particular for bridge-type oscillators utilizing a double T bridge of the RC or RL element type.

171	... With variable response:

	This subclass is indented under subclass 170. Subject matter wherein at least one of the filter impedance units is made adjustable in order to vary the response of the filter.

172	.. RC or RL type:

	This subclass is indented under subclass 167. Subject matter wherein the filter parameters are limited to combinations of resistance and capacitance or to combinations of resistance and inductance.

173	.. Synchronous filters:

This subclass is indented under subclass 167. Subject matter wherein the parameters of the filter are cyclically connected or disconnected.

(1) Note. The response (e.g., bandwidth, center frequency, harmonic rejection, etc.) is determined both by the magnitude of the filter parameters and by the rate at which the connections or disconnections are made.

174	.. With variable response:

	This subclass is indented under subclass 167. Subject matter wherein at least one of the filter parameters is made adjustable in order to vary the response of the filter.

175	.. Resonant, discrete frequency selective type:

This subclass is indented under subclass 167. Subject matter which include resonant series and/or parallel inductance and capacity networks which offer a low impedance path to energy of a particular frequency or of a plurality of separate discrete frequencies and/or offer a high impedance path to energy of a particular frequency or of a plurality of discrete frequencies.

(1) Note. This subclass includes filters under its definition in which means are incorporated for sharpening the tuning of the resonant circuits as by compensating for the resistance in such circuits.

(2) Note. The filters in this subclass are especially designed to pass only a single discrete frequency or a plurality of discrete frequencies but not a continuous band, or to eliminate one or more discrete frequencies from a band of frequencies.

SEE OR SEARCH THIS CLASS, SUBCLASS:

197+,

for similar filters utilizing electromechanical transducers.

SEE OR SEARCH CLASS:

330,	Amplifiers, subclasses 302+ for transistor amplifiers with frequency responsive coupling; subclasses 94 and 109 for amplifiers with frequency responsive feedback means; subclass 154 for cascaded amplifiers having a resonant means in an interstage coupling circuit; subclasses 157+, 185+, and 192+, particularly subclasses 167, 189, and 196 for coupling circuits with resonant circuit means.
331,	Oscillators, subclass 76 for oscillators, combined with an output coupling network including a harmonic selecting filter.
334,	Tuners, appropriate subclasses for tuners adapted to be used in wave energy apparatus, also see the reference note to Class 334 in the search notes of subclass 167 .

176	... Including specific frequency rejection means:

	This subclass is indented under subclass 175. Subject matter which include circuitry, provided for rejecting harmonics or for providing discrete transmission zeroes or attenuation poles within, at the edge of, or outside of, a prescribed filter pass band.

177	.. Transformer coupled:

This subclass is indented under subclass 167. Subject matter which include a mutual inductance link of the lumped type between the input and output of the filter.

(1) Note. The filters in this subclass are usually of the band-pass type, wherein the band-pass effect is due to the coupling between resonant circuits (e.g., intermediate frequency transformer systems with more than critical coupling between tuned primary and secondary circuits). The mutual inductance link need not be between the resonant circuits of the filter but may constitute the input or output coupling, the coupling between the resonant circuits being capacitive.

(2) Note. Wave filters wherein the mutual inductance link is of the long line type are not in this subclass but will be found in subclasses 125+ for branched circuit impedance matching networks; subclass 26 for balanced to unbalanced circuit conversion; subclasses 33+ for impedance matching networks; and subclasses 202+ for wave filters.

SEE OR SEARCH THIS CLASS, SUBCLASS:

197+,

for electromechanical transducer-type filters involving transformer coupling.

SEE OR SEARCH CLASS:

323,	Electricity: Power Supply or Regulation Systems, subclasses 247 , 301, 305, 328, and 355 for current and/or voltage magnitude control systems including transformers, and for miscellaneous transformer systems.
330,	Amplifiers, subclasses 154 , 165+, 188+, and 195+ for amplifiers having transformer coupling.
336,	Inductor Devices, appropriate subclasses for transformers which are not designed to be frequency responsive.
379,	Telephonic Communications, subclasses 443+ for induction coils combined with the structure of telephone instruments.

178	... Including bandwidth adjusting, shaping, or stabilization means:

	This subclass is indented under subclass 177. Subject matter wherein means are provided for adjusting the bandwidth or for maintaining constant bandwidth when circuit parameters are intentionally varied or when circuit parameters vary as a result of fluctuations in ambient conditions.

179	... With permeability tuning means:

	This subclass is indented under subclass 177. Subject matter wherein means are provided for varying the permeability of the mutual inductance link.

180	... With variable coupling means:

This subclass is indented under subclass 177. Subject matter wherein means are provided to adjust the degree of coupling between circuit elements or groupings of circuit elements.

(1) Note. This subclass includes means to vary either inductive coupling, capacitive coupling, resistive coupling, or any combinations of such coupling.

181	.. Smoothing type (e.g., direct current power supply filters or decoupling filters):

This subclass is indented under subclass 167. Subject matter having shunt capacitance or series inductance, or both, usually designed to pass direct current and to reduce the effect of any undesired alternating or pulsating current superimposed on the direct current or to pass direct current and low frequency alternating current or pulsating current and to reduce the effect of an undesired higher frequency alternating or pulsating current.

(1) Note. Such filters usually have no resonant relationship between the inductance and capacitance over the range of applied frequencies.

(2) Note. These filters are usually of the "brute force" type, utilizing an excess inductance and/or capacitance. They are generally low pass, being adapted to pass direct current and to reduce the effect of any undesired alternating current superimposed on the direct current.

(3) Note. Included are systems with a smoothing-type filter combined with a passive network means to regulate the current or voltage applied to or abstracted from the filter.

SEE OR SEARCH CLASS:

323,	Electricity: Power Supply or Regulation Systems, if the circuit which performs the smoothing action does so only by "bucking out" or balancing the undesired components, classification is in Class 323.
330,	Amplifiers, subclass 141 for amplifiers having smoothing circuits in the bias control path; subclass 142 for amplifiers including self-biasing circuits; and subclasses 199+ for amplifiers having significant power or bias supply means which may include significant details of smoothing filters.
363,	Electric Power Conversion Systems, subclasses 39+ for conversion systems, (i.e., rectification or decertification) in combination with smoothing-type filters.

182	... Feedthrough type:

This subclass is indented under subclass 181. Subject matter structured so as to include a central conductor concentrically surrounded by a capacitive or inductive element or by combinations of such elements.

(1) Note. These filter structures are usually adapted to be mounted in a partition, wall, or bulkhead, or to be mounted within a connector assembly.

183	.... Resiliently mounted components:

This subclass is indented under subclass 182. Subject matter wherein the central conductor or the inductive or capacitive elements are engaged to each other by resilient mounting structures.

(1) Note. The resilient mounting structures may include conductive or nonconductive elements providing for relative ease in assembling or disassembling of filter components and/or for providing relative ease in assembling filter components within a connector structure.

184	... Monolithic structure:

	This subclass is indented under subclass 181. Subject matter wherein inductive or capacitive elements are integrated on or within a common substrate or support.

185	.. Having significant physical structure:

This subclass is indented under subclass 167. Subject matter wherein the geometry of individual parameters or the physical distribution of such parameters is critical to obtaining the desired delay.

(1) Note. Included here would be inductive parameters having a specific core structure and/or winding geometry (i.e., low capacity windings).

186	. Electromechanical filter:

This subclass is indented under subclass 24. Subject matter including at least one electrical wave driven mechanical vibrator as a frequency determining element, providing free transmission of electric waves of a single frequency or band of frequencies (which may include zero frequency) while attenuating substantially electric waves having other frequencies, or attenuating substantially electric waves of a single frequency or band of frequencies (which may include zero frequency) while permitting free transmission of electric waves having other frequencies, and systems within the class definition which include such networks.

(1) Note. In many of the devices in this and the indented subclass, the electrical wave energy is converted into mechanical energy which is transmitted to a means for reconverting the mechanical energy to electrical wave energy. The mechanical energy transmitting means may be a bar, rod, fluid, etc. The mechanical transmission member determines the frequency of the energy transmitted.

SEE OR SEARCH THIS CLASS, SUBCLASS:

148+,

for delay networks of the electromechanical transducer type which are analogous to wave filters.

SEE OR SEARCH CLASS:

178,	Telegraphy, subclass 49 for telegraph systems utilizing vibrating elements for transmitting undulating currents.
181,	Acoustics, subclasses 207+ for mufflers and sound filters, see subclass 207 for rods designed to transmit mechanical vibrations and to damp out other mechanical vibrations and designed to act as mechanical filters.
310,	Electrical Generator or Motor Structure, subclasses 311+ for piezoelectric devices; and subclass 26 for the miscellaneous magnetostrictive devices.
318,	Electricity: Motive Power Systems, subclass 118 for magnetostrictive motors; and subclass 116 for piezoelectric motors.
322,	Electricity: Single Generator Systems, in the appropriate subclasses for electromechanical transducers of the motor generator type.
323,	Electricity: Power Supply or Regulation Systems, subclasses 201 through 204for dynamoelectric systems.
330,	Amplifiers, subclass 174 for amplifier systems having an electromechanical transducer coupling element; magnetostrictive means in an amplifier system are classified in subclass 60.
331,	Oscillators, appropriate subclasses particularly subclasses 73 , 116, 139, and 154+ for oscillators employing an electromechanical resonator or transducer as an element thereof.
336,	Inductor Devices, subclass 20 for inductors having magnetostrictive structure.
367,	Communications, Electrical: Acoustic Wave Systems and Devices, subclass 141 for underwater vibration transducers.
381,	Electrical Audio Signal Processing Systems and Devices, subclasses 337+ for telephone transmitters and receivers with mechanical sound amplifying means (e.g., harmonic vibrators); and subclasses 190 and 355+ for telephone transmitters and receivers using magnetostrictive effects.

187	.. Using bulk mode piezoelectric vibrator:

This subclass is indented under subclass 186. Subject matter wherein the wave driven mechanical resonator is a piezoelectric body subject to changes in its transverse and/or longitudinal dimension(s) under the influence of an external electric field.

(1) Note. The dimensional deformations of the piezoelectric vibrator are accompanied by mechanical bulk wave mode resonances, such resonances may be of the transverse, longitudinal, sheer, radial, or plate mode type.

(2) Note. Excluded from this subclass are surface acoustic wave filters wherein mechanical deformation is realized substantially only along the free surface of a piezoelectric body and no significant bulk mode resonance effects are realized.

SEE OR SEARCH CLASS:

310,	Electrical Generator or Motor Structure, subclass 323.19 for a piezoelectric element forming a resonant structure used to convert electric energy into sound energy or a piezoelectric element combined with specific means to conduct sound energy.

188	... With means for varying response:

	This subclass is indented under subclass 187. Subject matter wherein the filter bandwidth, center frequency, or phasing may be adjusted by mechanically or electrically variable parameters.

189	... Plural coupled vibrators:

	This subclass is indented under subclass 187. Subject matter wherein a plurality of vibrators are electrically or mechanically intercoupled so as to provide a composite response dependent on the contribution of each vibrator.

190	.... Lattice structure:

This subclass is indented under subclass 189. Subject matter having four circuit element branches connected in series to form a closed circuit, two nonadjacent junction points serving as input terminals while the remaining two junctions serve as output terminals.

(1) Note. At least two of the circuit element branches include a piezoelectric vibrator.

(2) Note. Two of the circuit branches may be formed by a transformer winding having a mid-tap, the mid-tap forming one of the input or output terminals, and the other winding of the transformer forming the output or input connecting means. See Fig. 4 below.

(3) Note. Included are for example:

Image 1 for class 333 subclass 190

Image 2 for class 333 subclass 190

Image 3 for class 333 subclass 190

Image 4 for class 333 subclass 190

191	.... Monolithic structure:

	This subclass is indented under subclass 189. Subject matter wherein a plurality of coupled vibrators are formed on a common piezoelectric body.

192	..... With electrical coupling:

This subclass is indented under subclass 191. Subject matter wherein the vibrators include electrical intercoupling.

(1) Note. The vibrators may also include mechanical coupling.

193	.. Using surface acoustic waves:

This subclass is indented under subclass 186. Subject matter wherein mechanical wave energy within a desired frequency band is transmitted in the form of acoustic waves propagating principally along a free surface or a guiding substrate.

(1) Note. The substrate is usually piezoelectric or comprises a surface coated with material having piezoelectric properties.

(2) Note. The surface waves are excited by transducers having a desired frequency selectively.

194	... Including spurious signal prevention or reduction means:

	This subclass is indented under subclass 193. Subject matter including structure for minimizing undesired electrical or mechanical mode coupling.

195	... With wave-modifying means (e.g., reflectors, resonators, diffractors, multistrip couplers, etc.):

This subclass is indented under subclass 193. Subject matter including structure for modifying the amplitude, phase velocity, or propagation path of surface acoustic wave energy along the wave propagation path.

(1) Note. Included here are structures to establish surface acoustic wave resonance on selected portions of the propagation path.

196	... With response weighting means:

	This subclass is indented under subclass 193. Subject matter including significant structure for adjusting the amplitude and/or phase versus frequency transmission characteristics of the filters.

197	.. Plural mechanically coupled bar, plate, or rod-type resonating means:

This subclass is indented under subclass 186. Subject matter wherein plural mechanical vibrators structured in the form of bars, rods, or plates are mechanically intercoupled.

(1) Note. The individual vibrators may have the same or different periods of vibration.

198	... Plural interresonator coupling paths:

This subclass is indented under subclass 197. Subject matter wherein some of the vibrators are coupled to each other along a plurality of mechanical wave coupling paths.

(1) Note. As an example, two rods or plates are intercoupled at more than one point (i.e., two end points of one vibrator are mechanically coupled to two end points of a second vibrator).

199	... Plural mechanically coupled disk resonators:

	This subclass is indented under subclass 197. Subject matter wherein plural disk-shaped vibrators are mechanically intercoupled.

200	.. Reed- or fork-type resonators:

	This subclass is indented under subclass 186. Subject matter wherein the vibrators are either elongated planar flexural mode structures having a relatively large ratio of length to width and thickness or are structured so as to resemble the tines of a fork.

201	.. Magnetostrictive wave transmission path:

	This subclass is indented under subclass 186. Subject matter wherein mechanical wave energy is transmitted by a vibrator comprised of magnetostrictive material.

202	. Wave filters including long line elements:

This subclass is indented under subclass 24. Subject matter including elements having distributed parameters and permitting free transmission of electric waves of a single frequency or band of frequencies (which may include zero frequency) while attenuating substantially electric waves having other frequencies, or attenuating substantially electric waves of a single frequency or band of frequencies (which may include zero frequency) while permitting free transmission of electric waves having other frequencies, and systems within the class definition which include such networks.

(1) Note. Tuners, which are closely analogous to the wave filters in the class, are classified in Class 334, Tuners. The tuners in Class 334 may include one or more long line elements in addition to a lumped inductance or capacitance element, or the tuner may consist of a distributed parameter type tuning unit which is adjusted in discrete, distinct steps. Two or more distributed parameter type tuner units which are of the continuously variable type and which are ganged together mechanically and/or electrically so as to have their mean resonant frequency adjusted in unison are properly classified in Class 334. Where only the bandwidth of the filter is varied without varying the means resonant frequency, classification is in this class (333).

(2) Note. Filters combined with circuits having other functions classified in other classes are excluded and will be found in other classes. See the classes referred to under "Search Class" below. Note the exception in the case of a mere current and/or voltage control network combined with a filter in (4) Note.

(4) Note. Filters in combination with means merely to control the magnitude of the current and/or voltage in the network are included in this and the indented subclass.

SEE OR SEARCH THIS CLASS, SUBCLASS:

1+,	for plural channel systems which include filters and for filters with plural input and/or output terminals.
19,	for differentiating or integrating networks which are analogous to wave filters.
20,	for wave shaping networks which are analogous to wave filters and which may include wave filters.
28,	for equalizing networks which are analogous to wave filters.
100+,	where the filter includes branching means (e.g., a single input with plural outputs).
126,	for resonant filter networks for matching the impedance in branched circuits, and branched circuits with line sections analogous to wave filters for impedance matching purposes.
132+,	for branched circuits which include filters.
156+,	for delay networks having long line elements analogous to wave filters.
219+,	for resonators.
236+,	for long lines.
245+,	for long line elements.

SEE OR SEARCH CLASS:

327,	Miscellaneous Active Electrical Nonlinear Devices, Circuits, and Systems, particularly subclasses 552+ for unwanted signal suppression by an active filter which may utilize a transistor or an electron tube.
330,	Amplifiers, subclasses 53+ for amplifier systems with long line element coupling means.
331,	Oscillators, subclasses 96+ which include distributed parameters.

203	.. Digital structure:

	This subclass is indented under subclass 202. Subject matter wherein the filter structure includes a plurality of electromagnetically coupled bar-or strip-type resonator sections aligned perpendicularly to the direction of wave propagation.

204	.. Stripline or microstrip:

This subclass is indented under subclass 202. Subject matter wherein the filter structure includes a long line of the type having planar conductors.

(1) Note. Examples of such lines are strip-lines, wherein a flat conductor is included between two ground planes, or microstrip lines, wherein a flat conductor coacts with a single ground plane.

205	... Tunable:

	This subclass is indented under subclass 204. Subject matter wherein the filter structure includes electrically or mechanically variable parameters to provide an adjustable amplitude versus frequency characteristic.

	This subclass is indented under subclass 202. Subject matter including a line structure comprising a conductor coaxially aligned with an outer cylindrical conductive sheath.

207	... Tunable:

	This subclass is indented under subclass 206. Subject matter wherein the filter structure includes electrically or mechanically variable parameters to provide an adjustable amplitude versus frequency characteristic.

208	.. Waveguide:

This subclass is indented under subclass 202. Subject matter wherein the filter structure includes a hollow dielectric tube, a hollow metal tube, or a solid dielectric designed to propagate electrical waves having an electric or magnetic field component extending in the direction of propagation and wherein the outer surfaces of the tube or solid dielectric serve as boundaries for the electromagnetic fields.

(1) Note. Included in this subclass would be filters employing dielectric rods or dielectric clad conductors wherein the propagation of energy is substantially confined to the immediate neighborhood of the rod or dielectric clad conductor.

209	... Tunable:

	This subclass is indented under subclass 208. Subject matter wherein the filter structure includes electrically or mechanically variable parameters to provide an adjustable amplitude versus frequency characteristic.

210	... Including evanescent guide sections:

	This subclass is indented under subclass 208. Subject matter wherein a waveguide section has reduced or negligible transmission due to the waveguide section being operated below its frequency cutoff point.

211	... Including frequency selective absorbing means:

	This subclass is indented under subclass 208. Subject matter wherein means are provided to dissipate or absorb wave energy of a given frequency or band of frequencies.

212	... Including directly coupled resonant sections:

	This subclass is indented under subclass 208. Subject matter wherein the filter structure includes resonant cavities directly coupled by slots or irises.

24C	. Capacitive coupling

	This subclass has no definition.

213	NEGATIVE RESISTANCE OR REACTANCE NETWORKS OF THE ACTIVE TYPE:

This subclass is indented under the class definition. Systems including active elements for producing, across at least two of the system terminals, a negative resistance and/or an inductance or capacitance which may be positive or negative.

(1) Note. This subclass does not include dynamoelectric machine systems which are used as a reactance element.

SEE OR SEARCH CLASS:

307,	Electrical Transmission or Interconnection Systems, subclasses 401+ for nonlinear reactance systems which may exhibit negative resistance characteristics.
323,	Electricity: Power Supply or Regulation Systems, subclasses 212 through 219for phase shift systems.
327,	Miscellaneous Active Electrical Nonlinear Devices, Circuits, and Systems, appropriate subclasses for miscellaneous circuits utilizing negative resistance devices.
330,	Amplifiers, subclasses 75+ for feedback amplifiers of the vacuum, tube type, particularly subclasses 82, 93, 101, 104, and 112 for positive feedback amplifiers; and subclasses 291+ for transistor feedback amplifiers.
331,	Oscillators, subclasses 86+ for magnetron-type oscillators which may utilize negative resistance effects; subclass 115 for transistor oscillators of the negative resistance type; subclasses 126+ for oscillators utilizing the negative resistance characteristic of a gaseous space discharge; and subclasses 132+ for negative resistance or negative transconductance oscillators in general. Subclasses 1+ of Class 331 provide for automatic frequency stabilized oscillators many of which utilize adjustable reactance tubes, indented subclass 36 provides for particular frequency control means (e.g., reactance tubes, saturable inductors, etc.); and subclass 180 provides for oscillators in general including frequency adjusting means of the reactance tube type.
332,	Modulators, particularly subclasses 140 and 142+ for reactance tubes in frequency modulators, subclasses 147+ for reactance tubes in phase modulators, and subclass 175 for reactance tubes in amplitude modulators.
334,	Tuners, subclasses 14+ for tuners utilizing reactance tube networks.

214	. Simulating specific type of reactance:

	This subclass is indented under subclass 213. Subject matter wherein a positive-valued inductance or capacitance is produced.

215	.. Using gyrator:

This subclass is indented under subclass 214. Subject matter employing a nonreciprocal circuit of the type that produces at one point the positive inversion of the impedance at a second point (i.e., a positive impedance inverter).

(1) Note. A gyrator is a four-terminal, two-port nonreciprocal network which may be defined as follows:

(a) The core is deformed.

wherein R₁ and R₂ are transfer impedances whose product determines the gyration constant K.

216	. Having negative impedance:

	This subclass is indented under subclass 213. Subject matter wherein a negative-valued impedance is produced across two of the system terminals.

217	.. Providing negative resistance:

	This subclass is indented under subclass 216. Subject matter wherein the negative impedance is a negative resistance.

81R	ATTENUATORS:

This subclass is indented under the class definition. Devices and networks consisting of one or more elements which exhibit only a positive resistance effect and which reduce the intensity of the energy passing through the device by dissipation, (a) the elements being proportioned to permit a change in their value to control the energy loss while maintaining substantially constant input and/or output impedance of the device, and/or (b) the elements being proportioned to permit the device to be inserted in the circuit to provide an energy loss without introducing any reflections in the circuit, and/or (c) the elements being combined with a long line or long line element, and/or (d) the device or network having an impedance equal to the impedance of a specified long line and/or (e) the device or network is claimed as being particularly modified for use over a frequency band so that its characteristics are particularly related to frequency, and (f) systems within the class definition including such devices or networks.

(1) Note. The networks and devices of part 5 of the definitions may include means such as capacitors to compensate for deviations in attenuation caused by changes in frequency of the applied energy, so that the device or network acts as a pure resistance. The network or device may be modified to obtain uniform attenuation over a band of frequencies.

(2) Note. Included are T, H, pad, and ladder or lattice type networks as well as transmission line sections.

(3) Note. This subclass embraces devices wherein one or more of the elements include reactance to compensate for any inherent reactance of the element or elements, see (1) Note.

(4) Note. If the device or network does not maintain a constant input and/or output impedance, or if it would introduce reflections into the transmission line, it is excluded from this class and will be found in Class 323 Electricity: Power Supply or Regulation Systems.

SEE OR SEARCH THIS CLASS, SUBCLASS:

13,	for resonator type breakdown discharge systems, which include attenuation networks.
14,	for amplitude compression and expansion systems which include attenuation networks.
15,	and 16, for pilot controlled systems which include attenuation networks.
17+,	for automatically controlled systems which may include attenuation networks.
22,	for transmission line terminations which dissipate the applied energy.
24+,	for adjustable reactive type coupling networks in general, see especially subclass 28 for equalizer networks.

SEE OR SEARCH CLASS:

181,	Acoustics, appropriate subclasses, for devices for attenuating sound, see subclass 206 for mufflers.
323,	Electricity: Power Supply or Regulation Systems, see (4) Note above.
330,	Amplifiers, appropriate subclasses under 157+, 185+ and 192+ for amplifiers having significant coupling which may include attenuators.
338,	Electrical Resistors, appropriate subclasses, for electrical resistors, per se; and subclasses 68+ for mechanically variable resistors including potentiometers and rheostats.

81A	. Coaxial or microstrip

	This subclass has no definition.

81B	. Waveguide type

	This subclass has no definition.

218	FREQUENCY MULTIPLIERS:

This subclass is indented under the class definition. Subject matter wherein the device has a single input and single output and the frequency of the output wave is normally a whole number multiple of the input frequency.

(1) Note. The device must be a long line element and use a nonlinear solid-state device for multiplying.

219	RESONATORS (DISTRIBUTED PARAMETER TYPE):

This subclass is indented under the class definition. Devices comprising conductive enclosures, cavities, or wave transmission line sections of the two terminal types and having distributed inductance and capacitance, the line sections being terminated in other than the characteristic impedance of the line sections, the devices presenting resonant characteristics to the exciting source of wave energy, and systems within the class definition which include such devices.

(1) Note. This subclass includes resonators even if they are provided with tuning means and designated as tuners.

SEE OR SEARCH THIS CLASS, SUBCLASS:

245+,

for long line elements which are terminated in other than their characteristic impedance and which are nonresonant, i.e., transmission line elements which are effectively inductances or capacitances, such as being 1/8 of a wave-length long.

SEE OR SEARCH CLASS:

315,	Electric Lamp and Discharge Devices: Systems, subclasses 4+ for cathode-ray tubes which have structurally combined therewith a resonant structure; subclasses 39+ for electronic tubes having structurally combined therewith a resonant transmission line; and subclasses 39.51+ and 40 for other electronic tubes which include resonant structures.
330,	Amplifiers, subclasses 53+ for amplifiers having distributed parameter coupling which may be resonant; subclass 45 for electron beam type amplifiers having cavity resonator coupling means; subclass 49 for amplifiers wherein the active element is a tube having distributed parameter characteristics which may be resonant.
331,	Oscillators, subclasses 5 , 6+, 9, 79+, 86+, 93, and 96+ for oscillator systems utilizing distributed parameter resonators as an element thereof.
332,	Modulators, particularly subclasses 129+ for resonators in frequency modulators and subclasses 163+ for resonators in amplitude modulators.
343,	Communications: Radio Wave Antennas, subclass 723 for single adjustable length electrically long linear antennas; subclasses 745+ for antennas with a variable reactance for tuning the antenna; subclasses 746 and 767+ for slot-type antennas which may include resonator structure; subclasses 790+ for sleeve-type antennas; subclasses 793+ for balanced doublet-type antennas which may have resonant characteristics; subclasses 825+ for fractional, multiple, or full wavelength-type antennas; and subclass 843 for antennas having an appreciable wave-length dimension.
455,	Telecommunications, subclasses 130+ for radio receivers using resonators, see particularly subclasses 325+ for frequency conversion means with distributed parameter elements which may be resonant.

219.1

. Dielectric type:

	This subclass is indented under subclass 219. Subject matter where the resonator device is a dielectric material body in which field configurations excited by the source of wave energy are substantially confined therein.

219.2

. Magnetic type:

	This subclass is indented under subclass 219. Subject matter where the resonator device possesses magnetic properties responsive to the exciting source of wave energy.

220	. Open wire or Lecher line:

	This subclass is indented under subclass 219. Subject matter wherein the line section is of the parallel wire type normally an integral number of half-wavelengths long so as to set up standing waves on the section.

221	.. With tuning:

	This subclass is indented under subclass 220. Subject matter wherein the resonator has means which can be adjusted to resonate or operate at a specified frequency.

222	. Coaxial or shielded:

	This subclass is indented under subclass 219. Subject matter wherein the resonator is of the two conductor type having a central conductor concentric with the resonator outer conductor.

223	.. With tuning:

	This subclass is indented under subclass 222. Subject matter wherein the resonator has means which can be adjusted to resonate or operate at a specified frequency.

224	... Having movable element:

	This subclass is indented under subclass 223. Subject matter wherein the frequency is adjusted by a movable element.

225	.... Using movable shorting means:

	This subclass is indented under subclass 224. Subject matter wherein short-circuiting means is included with the coaxial or shielded transmission line.

226	.... Using plunger, rod, or piston:

	This subclass is indented under subclass 224. Subject matter wherein the movable element is a plunger, rod, or piston.

227	. Cavity resonator:

This subclass is indented under subclass 219. Devices and systems where the resonator device is an enclosure or cavity so constructed that the field configuration excited within the boundaries of the device includes longitudinal as well as transverse field components.

SEE OR SEARCH CLASS:

315,	Electric Lamp and Discharge Devices: Systems, subclasses 5+ for cathode-ray tubes which have structurally combined therewith a hollow resonant structure (e.g., waveguide hollow resonator); subclasses 39+ for electronic tubes structurally combined with a waveguide section; and subclasses 39.51+ and 40 for other electronic tubes structurally combined with resonator structure (e.g., magnetrons).
330,	Amplifiers, subclass 45 for electron beam tube amplifiers coupled to a cavity resonator; and subclass 56 for amplifiers, generally having a resonator of the waveguide, cavity, or concentric line type.
331,	Oscillators, subclasses 5 , 6+, 81+, 86+, 93, and 96 for oscillator systems utilizing distributed parameter resonators, which resonators may be of the cavity or hollow waveguide type.
332,	Modulators, particularly subclasses 129+ for resonators in frequency modulators and subclasses 163+ for resonators in amplitude modulators.
343,	Communications: Radio Wave Antennas, subclasses 762 and 772+ for waveguide-type antennas; and subclass 771 for plural slot-type antennas with waveguide coupling.

228	.. With mode suppressor:

	This subclass is indented under subclass 227. Subject matter wherein means are provided to minimize or substantially eliminate extraneous modes of oscillation in cavity resonators.

229	.. With temperature compensation:

	This subclass is indented under subclass 227. Subject matter wherein the cavity resonator has thermal compensation means to substantially reduce the effects of temperature variations on the operating frequency.

230	.. With coupling:

	This subclass is indented under subclass 227. Subject matter wherein significant structure is included for effecting the transfer of oscillatory energy between the cavity resonator and another circuit.

231	.. With tuning:

	This subclass is indented under subclass 227. Subject matter wherein the cavity has means whereby the cavity can be adjusted to resonate or operate at a specified frequency.

232	... Having movable element:

	This subclass is indented under subclass 231. Subject matter wherein the frequency is adjusted by a movable element.

233	.... Using movable wall:

	This subclass is indented under subclass 232. Subject matter wherein the movable element is a wall that moves or is flexible.

234	. Temperature compensated:

	This subclass is indented under subclass 219. Subject matter wherein the resonator has thermal compensation means to substantially reduce the effects of temperature variations on the operating frequency.

235	. With tuning:

	This subclass is indented under subclass 219. Subject matter wherein the cavity of the resonator has means which can be adjusted to resonate or operate at a specific frequency.

This subclass is indented under the class definition. Structure providing a single channel of indefinite length for conveying and guiding wave energy, and having distributed electrical parameters so related or proportioned as to determine the wave propagating characteristics of the channel.

SEE OR SEARCH THIS CLASS, SUBCLASS:

12,	for long lines with means to eliminate interference currents therein or with means to minimize radiation therefrom.
22,	for dissipative terminations for transmission lines.
23,	for artificial lines simulating a transmission line.
26,	for coupling networks for connecting balanced to unbalanced circuits or vice versa which include a long line element.
27,	for transmission lines with coupling networks at the opposed ends.
33+,	for impedance matching networks which include a long line element.
202+,	for filters which include a long line element.

SEE OR SEARCH CLASS:

174,	Electricity: Conductors and Insulators, appropriate subclasses for conductor structure other than loaded lines and lines defined as having long line characteristics; see subclass 27 and 113+ for parallel or twisted conductor structures; subclasses 28 and 102+ for coaxial and shielded cable structure; subclasses 32+ for anti-inductive conductor structures; subclasses 37+ for underground conductor structures; and subclasses 40+ for overhead conductor structures.
178,	Telegraphy, for telegraph transmission line systems; and particularly subclasses 45+ for loaded circuits; subclass 63 for long cable systems; and subclass 69 for line-clearing and circuit-maintenance systems.
307,	Electrical Transmission or Interconnection Systems, appropriate subclasses, particularly subclass 146 and 147+ for miscellaneous systems of distribution with transmission lines usually of the electrically short type.
315,	Electric Lamp and Discharge Devices: Systems, subclasses 3.5+ and 4+ for transmission line sections structurally combined with cathode-ray tubes; and subclasses 39+ for electronic tubes which are structurally combined with a transmission line of the distributed parameter type.
324,	Electricity: Measuring and Testing, subclasses 51+ , 54, 66+, 95, and 600+ for arrangements to determine the electrical characteristics of transmission lines.
329,	Demodulators, subclass 322 for a frequency demodulator including distributed parameter structure and subclass 354 for an amplitude demodulator including distributed parameter structure.
330,	Amplifiers, subclasses 53+ for amplifiers coupled to a long line.
340,	Communications: Electrical, for miscellaneous electrical signaling systems which include a long line. Note subclasses 12.32 through 12.39and 538-538.17 for such systems where the signal is transmitted over a power line and subclass 320 for signaling using a fluid conduit to transmit the signal.
343,	Communications: Radio Wave Antennas, subclasses 700+ for antennas which may involve long lines.
379,	Telephonic Communications, for telephone transmission line systems; particularly subclasses 1.01 through 33for long line testing device, subclasses 90.01-108.02 for composite systems (e.g., telegraph and telephone), and subclass 398 for anti-inductive systems.

237	. Leaky lines:

This subclass is indented under subclass 236. Subject matter wherein the long line carries a travelling wave which is lightly coupled to a series of leakage apertures to create a concentrated, uniform, radiation field in the immediate vicinity of the aperture.

(1) Note. Many of the patents in this subclass are directed towards radiating energy from a coaxial cable in a building, tunnel, or mine and/or for vehicle communication.

SEE OR SEARCH CLASS:

343,	Communications: Radio Wave Antennas, subclasses 700+ for the structural details of the radiating aperture used in conjunction with the long line, e.g., subclasses 767+ for slots.

238	. Strip type:

This subclass is indented under subclass 236. Subject matter wherein the long line is of the type having planar conductors.

(1) Note. Examples of such lines are stripline, microstrip, slot line, and coplanar waveguide.

239	. Waveguide type:

This subclass is indented under subclass 236. Subject matter particularly adapted for propagating electric waves having an electric or magnetic field component extending in the direction of propagation.

(1) Note. The waveguide may be a hollow dielectric or metal tube or solid dielectric rod, the wave energy being propagated along the interior of the tube or rod and confined by the walls of the tube or rod.

240	.. Surface wave:

This subclass is indented under subclass 239. Subject matter for propagating, without substantial radiation, electromagnetic energy along the interface between two media having different physical properties (e.g., different permittivities).

(1) Note. While the electromagnetic field extends to infinity in a direction transverse to the guide, the energy density decreases with distance so that most of the energy propagation is in the immediate neighborhood of the interface.

(2) Note. Surface wave guiding structures may comprise dielectric clad conductive cylinders, conductive planes with parallel grooves or conductive cylinders with radial grooves, or a dielectric rod clad with a dielectric media of a different permittivity.

241	.. Flexible:

	This subclass is indented under subclass 239. Subject matter wherein the waveguide is articulated, segmented, or otherwise structured so as to permit desired bending without appreciable wave mode distortion and/or without appreciable characteristic impedance variation.

242	.. Circular or helical structure:

	This subclass is indented under subclass 239. Subject matter wherein the guide structure is a hollow conductive cylinder, a helical conductor, or a helical conductor located within a conductive screen.

243	. Shielded type:

This subclass is indented under subclass 236. Subject matter wherein the long line comprises at least one electrical conductor surrounded by an electrically conducting screen.

(1) Note. This subclass includes, for example, coaxial cable-type conductors and other transmission lines having one or more conductors surrounded by an outer metal sheath which is designed for use as a conductor.

SEE OR SEARCH THIS CLASS, SUBCLASS:

12,	for interference suppression and/or elimination systems which may include electrical screens or shields, and for conductor arrangements which involve shielding means or structure in addition to the conductor arrangement.

SEE OR SEARCH CLASS:

174,	Electricity: Conductors and Insulators, particularly subclasses 28+ for the structure of coaxial or concentric-type cables having a fluid or vacuum; subclass 36 for electrically shielded or screened conductors; and subclasses 102+ for cables or conductor structure having a conductive armor or sheath.
315,	Electric Lamp and Discharge Devices: Systems, subclasses 4+ for cathode-ray tubes which have structurally combined therewith a coaxial cable section; and subclasses 39+ for other electronic tubes which have structurally combined therewith a coaxial cable section.
343,	Communications: Radio Wave Antennas, subclasses 841+ for antennas with an electrical shield; subclass 851 for antennas with a coupling network including a radiation suppressor; and subclass 905 for antennas combined with a transmission line which may include a shield for the transmission line.

244	.. Including spaced, electrically compensated, internal support means:

	This subclass is indented under subclass 243. Subject matter having spaced apart support means for an internal conductor, wherein the support means and/or ancillary reactance means function to reduce the effects of impedance discontinuities normally resulting from the use of a discontinuous support structure.

245	LONG LINE ELEMENTS AND COMPONENTS:

This subclass is indented under the class definition. Components and elements not constituting a complete network which are limited by claimed structure to use in long lines and which are not otherwise classified, and also long line elements.

(1) Note. Included in this subclass are structures and devices for modifying the characteristics of a transmission line at a particular location, for example, line short-circuiting switches, line-shorting plugs, impedance elements, and long line elements which are terminated in other than their characteristic impedance and are nonresonant (e.g., a short-circuited line 1/8 of a wavelength long).

SEE OR SEARCH THIS CLASS, SUBCLASS:

13,	for resonator type breakdown discharge device networks for short circuiting a long line.
22,	for dissipating terminations for long lines.
101+,	for branched circuits having switching means.
219+,	for resonators.
236+,	for long lines.

SEE OR SEARCH CLASS:

174,	Electricity: Conductors and Insulators, appropriate subclasses for conductors, housing insulators, conductor joints, and end structure where no significant wave propagation characteristic limiting the structures to use with long lines is claimed.
200,	Electricity: Circuit Makers and Breakers, appropriate subclasses for switching structure in general.
285,	Pipe Joints or Couplings, appropriate subclasses for couplings for coaxial lines or for waveguides where no significant electrical features are claimed.
329,	Demodulators, subclass 322 for a frequency demodulator including distributed parameter structure and subclass 354 for an amplitude demodulator including distributed parameter structure.
330,	Amplifiers, subclasses 53+ for amplifiers with distributed parameter coupling means including subject matter involving structural details of such means.
343,	Communications: Radio Wave Antennas, subclasses 907+ for antenna components.
439,	Electrical Connectors, for transmission line electrical connectors where no significant wave propagation characteristic are claimed which limit the structure to use with long lines.

246	. Strip type:

This subclass is indented under subclass 245. Subject matter wherein the long line is of the type having planar conductors.

(1) Note. Examples of such lines are stripline (two ground planes), microstrip (one ground plane), slot lines, or coplanar waveguides.

SEE OR SEARCH THIS CLASS, SUBCLASS:

238,	for strip-type lines, per se.

247	.. Semiconductor mounts:

This subclass is indented under subclass 246. Subject matter wherein a strip-type board is used to hold or support a solid-state device such as a transistor.

SEE OR SEARCH CLASS:

257,	Active Solid-State Devices (e.g., Transistors, Solid-State Diodes), subclasses 662 through 664.

248	. Waveguide elements and components:

This subclass is indented under subclass 245. Components and elements which are limited to use with waveguides, and also waveguide elements.

(1) Note. A waveguide may be a hollow dielectric or metal tube or a solid dielectric rod, the wave energy being propagated along the interior of the tube or rod and confined by the walls of the tube or rod.

SEE OR SEARCH THIS CLASS, SUBCLASS:

113,	for directional couplers having parallel-guide waveguides.
114,	for directional couplers having crossed-guide waveguides.
122,	for hybrid-type networks using waveguide.
135,	for frequency separation utilizing long line elements including waveguide elements.
157+,	for delay lines including long line waveguide elements.
239+,	for types of waveguide.

SEE OR SEARCH CLASS:

138,	Pipes and Tubular Conduits, subclasses 100 through 178for waveguide structures and accessories which are not limited to electrical use.
174,	Electricity: Conductors and Insulators, appropriate subclasses for conduits and transmission line structure limited to electrical use but not having long line characteristics.
285,	Pipe Joints or Couplings, appropriate subclasses for pipe couplings not limited to electrical use.
329,	Demodulators, subclass 322 for a frequency demodulator including distributed parameter structure and subclass 354 for an amplitude demodulator including distributed parameter structure.
343,	Communications: Radio Wave Antennas, subclass 783 for waveguide-type antennas with internal wave refraction means; and subclass 785 for waveguide-type antennas which are of the dielectric type.