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Abstract

To permit simultaneous transmission of command codes, in binary command words, with traffic or other announcements, being broadcast over an FM transmitter which has a 57 kHz subcarrier AM modulated by an announcement recognition (AR) signal, for example 125 Hz, use is made of the long response time of AR switching elements to provide, before the AR switching element (13) can respond, decoding of a command word at a clock rate which is fast with respect to the response time of the long switching time constant switching element (13). This fast response is, preferably, accomplished by a counter (18) which has only the number of count positions corresponding to the bits in the command word, then provides an overflow to block a memory (15) in which the bits are being stored; a second counter (20)--or a continuing portion of the counter--counting at the clock rate for a period of time longer than the response time of the switching element (13) to then cause unblocking of the memory, for subsequent reception of command words, which may occur during transmission of the AR signal, by merely short interruptions thereof, insufficiently long to prevent drop-out of the switching element (13) of the AR system. A decoder (30) is connected to decode the expected command words, but reject AR signals, the characteristics of both of which are known.

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First Claim