SELECTIVE CALLING SYSTEM PROVIDING AN INCREASED NUMBER OF CALLING CODES OR AUXILIARY INFORMATION TRANSFER

摘要

The selective calling system includes a transmitter having first and second signal generators providing sinusoidal and rectangular signals which are combined to form a modulated calling signal. Each receiver of the system includes a first demodulator which demodulates the modulated calling signal and a second demodulator which demodulates the rectangular signal. A frequency selective device connects the first demodulator to a first input of an AND gate and a repetition rate selective device connects the second demodulator to a second input of the AND gate. If the demodulated frequency and repetition rate are within the passbands of the devices, the AND gate provides a turn-on signal which allows primary information to be reproduced by the receiver. The system can be modified so that auxiliary information is transferred to the receivers by the calling signal.