at least one combining circuit coupled to receive a plurality of RF signals each at the same frequency, wherein the plurality of RF signals are output from respective ones of a plurality of base transceiver stations for transmission, wherein the combining circuit is configured to combine the plurality of RF signals into a combined signal that is connected to an output port for supply to an antenna assembly, wherein the combining circuit combines the plurality of RF signals into the combined signal such that the plurality of RF signals are transmitted in a time division duplex (TDD) manner via the antenna assembly;

a plurality of frequency selective RF power detectors configured to receive an output from a respective one of the plurality of base transceiver stations, wherein each RF power detector is further configured to generate an output that indicates presence or absence of RF power at the frequency in the output of the respective base transceiver station;

a controller coupled to the plurality of frequency selective RF power detectors, wherein the controller is configured to generate a control signal based upon the outputs of the plurality of RF power detectors; and

an oscillator coupled to the controller and to the combining circuit, wherein the oscillator is configured to be responsive to the control signal generated by the controller to generate a carrier signal at the frequency for use in synchronizing transmission of the individual RF signals in the combined signal via the antenna assembly;

wherein the controller is configured to generate the control signal that turns off the oscillator when any of the plurality of RF power detectors detects absence of RF power at the frequency so that the oscillator does not generate the carrier signal at the frequency, and is configured to generate the control signal that turns on the oscillator when all of the plurality of RF power detectors detect presence of RF power at the frequency so that the oscillator generates the carrier signal at the frequency.