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Abstract

An attention signal receiver in which emergency broadcast transmissions are detected from various locations. A scanning circuit sequentially activates means to produce a plurality of oscillating frequencies which mix or beat with the incoming r.f. signals. An attention signal is a two tone signal that includes both a 960 H.sub.z frequency signal and a 853 H.sub.z frequency signal. The audio stage of the receiver is connected to a two tone decoder that passes only a 960 H.sub.z signal and a 853 H.sub.z signal. A squelch circuit is also connected to the audio stage of the receiver. Connected to the output of the tone decoder is a one second time delay circuit and a ten second time delay circuit. If an attention signal is detected for a period of time in excess of 1 second, the one second time delay circuit stops the scanning of the scanning circuit to lock in the receiver to the first carrier detected with an attention signal. The ten second time delay circuit normally disables the squelching circuit. If the detected attention signal continues for a period of time in excess of 10 seconds, the ten second time delay circuit enables the squelch circuit to operate an alarm.

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First Claim