a frame;

a conveyor that is disposed movably on the frame and that conveys items through a path of travel, each item having at least one respective radio frequency identification tag disposed thereon;

a first antenna disposed proximate the path of travel so that the first antenna radiates first radio frequency signals into a first area through which the items pass in the path of travel;

a second antenna disposed proximate the path of travel so that the second antenna receives first responses to the first radio frequency signals from the respective radio frequency identification tags on the items, wherein each first response includes information that identifies a class protocol of the radio frequency identification tag from which said first response is received;

a third antenna disposed proximate the path of travel so that the third antenna radiates second radio frequency signals into a second area that is downstream from the first area with respect to the path of travel and through which the items pass in the path of travel;

a fourth antenna disposed proximate the path of travel so that the fourth antenna receives second responses to the second radio frequency signals from the respective radio frequency identification tags on the items;

at least one radio frequency transmitter that drives the first antenna to emit the first radio frequency signals into the first area and drives the third antenna to emit the second radio frequency signals into the second area;

at least one radio frequency receiver that

receives signals from the second antenna corresponding to the first responses and outputs first output signals corresponding to the first responses and including the information, and

receives signals from the fourth antenna corresponding to the second responses and outputs second output signals corresponding to the second responses; and

a processor that receives the first output signals and controls the at least one transmitter to drive the third antenna responsively to the first output signals.