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;

at least one antenna disposed proximate the path of travel so that the at least one antenna

radiates radio frequency signals into a first area through which the items pass and

receives responses to the radio frequency signals from radio frequency identification tags on the items passing through the path of travel;

a radio frequency transmitter that drives the antenna to emit the radio frequency signals into the first area;

a radio frequency receiver that receives signals from the antenna corresponding to the responses received by the antenna from the respective radio frequency identification tags and outputs first signals corresponding to the responses; and

a processor that receives the first signals from the receiver,

wherein the processor is programmed to

associate a said first signal with a first said item based upon whether the processor receives the first signal from the receiver while at least a portion of the first item is within a predefined second area that includes at least part of the first area, and

for each of a plurality of said first items, define a length of the second area with respect to the path of travel based on a distance between the first item and a second item next following the first item in the path of travel.