Abstract: A voice operated switch having minimum signal amplification in the stages which separate the voice signals from the noise signals. The majority of amplification is then applied only to the syllabic rate voice component detected by an offset threshold in the syllabic rectifier-amplifier circuit to produce a two-state signal, one state representative of the presence of voice energy and the other state representative of the absence of voice energy. The two states are compared with a threshold voltage adjustable between a maximum and minimum voltage. A maximum and minimum setting allow a respective nontransmission and transmission of the voice signals irrespective of the presence or absence of such signals.

Abstract: A circuit for detecting data such as FSK data which is not amplitude modulated. The circuit employs detectors for detecting the frequency domain characteristics, time domain characteristics and amplitude characteristics of the data signals so that a precise indication of the presence or absence of such data signals can be made. Further provided is a threshold control circuit which can override the indication of the presence or absence of data signals irrespective of whether such signals are in fact present or absent.