Importance

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Abstract

In a system for monitoring use of a video monitoring system, RF signals are injected into a cable converter and a VCR in order to detect channels selected by the cable converter and VCR. Installation of probes is not required for channel detection. Channel identification signals are also injected into the VCR and cable converter for recording by the VCR on videotape. Respective channel identification signals are provided to the cable converter and VCR with time multiplexing. The state of the 'TV/VCR' switch of the VCR is determined by injecting a code signal into the VCR and determining whether that signal is present in an RF video signal output by the VCR. The system includes a switch for interconnecting the cable converter, VCR and TV and also for coupling injection signals to respective inputs of the cable converter and VCR. The system also includes an injection signal receiver that detects signals injected into and passed through the VCR and cable converter for the purpose of channel detection. The receiver also receives data contained in channel identification signals. The receiver is selectively connectable to the VCR and the cable converter. Changes in the signal source for the cable converter and VCR are optionally detected by sampling and holding signal levels during certain horizontal blanking intervals of the signal output from the cable converter or VCR. Monitoring of a system that includes two VCRs is also disclosed.

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First Claim