Method and apparatus to determine the channel to which a TV tuner is tuned from a return loss ratio measurement circuit in a set top decoder. The method comprises generating a plurality of probe signals having frequencies spread throughput the TV channel band, preferably using harmonics of a zero order hold D/A converter. The return loss ratio of the reflected probe signals is then determined and stored as a signature for the TV channel and the signatures can subsequently be used along with new return loss ratio measurements to determine the TV channel to which a TV or VCR tuner is tuned.