Abstract: Disclosed is a tuned channel detector which includes a cable path between a radio frequency source and a receiver such as a TV, wherein the radio frequency source passes first through an attenuator and second through a signal selection module comprising two opposing directional couplers and a single-pole/double-throw switch. The channel to which the TV is tuned is determined by measuring the TV's local oscillator signal from the cable which feeds the radio frequency signal to the TV and, additionally or alternatively, by comparing the signal strength of the input and reflected TV carrier signals at and around the channels under test. Signal detection is further enhanced by modulating the signal mixed with the local oscillator with a tone and/or testing only during certain intervals such as the vertical synchronization interval or the power line cycle. A tone detector having a synchronous rectifier is used to detect low level local oscillator signals.

Abstract: Disclosed is a tuned channel detector which includes a cable path between a radio frequency source and a receiver such as a TV, wherein the radio frequency source passes first through an attenuator and second through a signal selection module comprising two opposing directional couplers and a single-pole/double-throw switch. The channel to which the TV is tuned is determined by measuring the TV's local oscillator signal from the cable which feeds the radio frequency signal to the TV and, additionally or alternatively, by comparing the signal strength of the input and reflected TV carrier signals at and around the channels under test. Signal detection is further enhanced by modulating the signal mixed with the local oscillator with a tone and/or testing only during certain intervals such as the vertical synchronization interval or the power line cycle. A tone detector having a synchronous rectifier is used to detect low level local oscillator signals.