Abstract: A signal locating apparatus for locating within a frequency band an input signal of a first frequency, the signal locating apparatus including a signal receiver for receiving the input signal. The signal receiver is characterized by having a relatively narrow bandwidth response of variable center frequency, the signal receiver being capable of generating a detected signal when the center frequency is substantially equal to the first frequency, the signal locating apparatus further including search device for varying the center frequency at a relatively high rate so as to cause the signal receiver to search for the presence of the input signal within a frequency band, the search device being operable in response to generation of the detected signal to stop the search for the presence of the input signal.

Abstract: A discriminating apparatus for discriminating a radiant information signal from a background signal, the discriminating apparatus including a radiation sensing means sensitive to an incident signal comprising both an information signal and a background signal and operative to generate an output sensing signal of a level related to the level of the incident signal, and detector means responsive to the sensing signal to detect an information signal component of the sensing signal from a background signal level component of the sensing signal.