Abstract: There is disclosed an aircraft selective calling decoder for decoding individual signal tones used in selectively signaling communication of a particular aircraft. The decoder is associated with a channel of receiving equipment in an aircraft and is responsive typically to a particular four-tone coded signal, the reception of which actuates the decoder indicating that an incoming communication is to be received. The decoder includes a dual path circuit which receives dual frequencies of each individual tone of the four-tone code and provides an output upon receipt of each tone for enabling the receiver following receipt of the proper four-tone code sequence. Filtering in each of the dual paths for each frequency of a tone is controlled by a microprocessor to eliminate the necessity for multiple individual filters.

Abstract: Peak-limiting AGC for increased average power SSB transmission is improved by deriving a gain-control signal using Hilbert transform detection techniques to obtain a modulated envelope signal which is compared with a peak clipping reference to form the limiting gain-control signal.