Abstract: A complete process is described for demodulating subsidiary communications authorization (SCA) radio signals. This process takes as an input an FM radio signal from a commercial FM telescoping type antenna. The signal is optimally processed through filtering, amplification, and dual detection circuitry to provide a high quality sub-carrier audio signal. Special matching is provided to set the signal's gain, noise figure, and injected distortion levels as a function of the antenna being extended or collapsed. Also, filtering of RF image and IF baseband signals is uniquely and efficiently performed in a radio receiver having an telescoping antenna and audio out line, an SCA radio turner has a matching filter between the antenna and a first FM discriminator to match the level of extension of the antenna, a phase-lock-loop circuit within a second FM discriminator following the first FM discriminator, and sub-carrier audio processing between the FM discriminator and the audio out line.