Patent ID: 6813475
Filing Date: 2004-11-02
Classification: H04B

Abstract:
An interference attenuating remote audience survey system for identifying radio stations to which tuners are tuned, said tuners having local oscillator (LO) signals emitted therefrom, and said system comprising:a controller configured to select one of said LO signals associated with one of said radio stations; a first antenna for sensing a first signal in a detection zone of said first antenna, said first signal including said one of said LO signals and an interference signal; a second antenna for receiving a second signal, said second signal including said interference signal; a shield element positioned between said second antenna and said detection zone for shielding said second antenna from receiving said one of said LO signals; a combiner in communication with each of said first and second antennas, said combiner subtractively combining said first and second signals to produce a third signal, said interference signal being attenuated from said third signal; a receiver in communication with said combiner and said controller, said receiver being configured to detect said selected one of said LO signals within said third signal to determine that one of said tuners is tuned to said one of said radio stations; and a phase shifter in communication with said combiner for providing a phase shift component to one of said first and second signals to substantially cancel a phase difference between said second signal and said interference signal within said first signal.