Apparatus for monitoring television receivers

Abstract

Apparatus for monitoring the use of television receivers to obtain information for the rating of television programs. The apparatus makes a comparison between the intercarrier frequency signal (i.e., phase) produced by extracting from an operating television receiver tuned to a channel the visual and aural IF frequencies and the respective intercarrier frequency signals (i.e., phase) produced by successively extracting from transmitting sources of television channels the visual and aural IF frequencies. The intermediate frequency signals of the television receiver are sampled and converted into an intercarrier frequency signal. A voltage controlled tuner is tuned to the radio frequency carriers of the various television channels in a hunting sequence. The output signals of the voltage controlled tuner are intermediate frequency signals, which are converted into intercarrier signals. When the intercarrier frequency emanating from the voltage controlled tuner is phase coherent with the intercarrier frequency signal emanating from the operating television receiver over a prescribed period of time, such as 10 seconds, then an identification is made of the channel to which the operating television receiver is tuned and this information is recorded.