Active system and method for detecting harmonics of RF broadcast station survey signals

A remote audience survey system for identifying a radio station to which a tuner is tuned, said tuner having local oscillator (LO) signals emitted therefrom, and said system comprising:

• a controller configured to select one of said LO signals associated with said radio station, said one LO signal exhibiting a fundamental frequency;
• a transmitter in communication with said controller, said transmitter including:
• a signal generator for producing said one LO signal;
• a modulator in communication with said signal generator for incorporating a modulation characteristic into said one LO signal to form a survey signal;
• and
• a first antenna in communication with an output of said modulator for broadcasting said survey signal;
• and
• a receiver in communication with said controller and having a second antenna configured to receive a broadcast signal, said receiver being configured to detect a harmonic of said fundamental frequency within said broadcast signal and verify that said detected harmonic includes said modulation characteristic to determine that said tuner is tuned to said radio station.

A remote audience survey method for identifying radio stations to which tuners are tuned, said tuners having local oscillator (LO) signals emitted therefrom, said LO signals being associated with said radio stations, and said radio stations having broadcast coverage areas, said method comprising:

• establishing a detection zone which is smaller than said broadcast coverage areas;
• selecting one of said LO signals associated with one of said radio stations, said one LO signal exhibiting a fundamental frequency;
• generating a survey signal in response to said selecting operation, said generating operation including:
• applying frequency modulation to said one LO signal to produce a frequency modulated LO signal;
• and
• pulsing said frequency modulated LO signal to produce said survey signal exhibiting frequency and amplitude modulation characteristics;
• setting a signal strength of said survey signal to have a transmission range substantially equivalent to said detection zone;
• broadcasting said survey signal;
• receiving a broadcast signal;
• detecting a harmonic of said fundamental frequency within said broadcast signal;
• and
• verifying that said detected harmonic includes said frequency and amplitude modulation characteristics to determine that one of said tuners in said detection zone is tuned to said one radio station.