Abstract: An FM broadcasting system is disclosed for transmitting a data signal simultaneously with an auxiliary audio program on the same subcarriers of an FM transmission channel. The main program is transmitted on the FM transmission channel carrier and the auxiliary audio program, which may be background music, is transmitted on the subcarriers in a conventional manner. According to the present invention, the data signal, which is added to the auxiliary audio program, is a binary digital information signal. This binary digital information signal is used to generate a signal which modulates the phase and amplitude of a data reference signal. The resulting phase transition of the modulated data reference signal represents the binary value of the binary digital information signal. The amplitude of the modulated data reference signal then is adjusted in an automatic gain control amplifier relative to the amplitude of a corresponding frequency range of the auxiliary audio program.

Abstract: A tamper resistant subscription television converter is made by connecting a bandstop filter in the Radio Frequency circuit of the converter. The filter, for attenuating one or more preselected subscription television channels is connected in series at a location in the Radio Frequency circuit such that tampering with it would affect the converter's alignment. The filter is tuned to obtain maximum attenuation of the preselected channels and the converter is aligned for proper reception of the remaining channels. Any attempt to disable the attenuator results in unacceptable reception of all channels. A preferred bandstop filter is a constant K, T section L-C filter.