Loudspeaking telephone with improved receive sensitivity

摘要

An improved loudspeaking telephone system including voice switching is disclosed. The system is bistably voice controlled by inversely regulating the impedances of variolossers in the transmit and receive channels, respectively. Hysteresis is added to the bistable control by the summation of receive and transmit signals across a plurality of unequal impedances that form part of an input control means. Circuitry forming the input control means also includes transmit noise guard circuit means useful in discriminating between ambient noise signals and syllabic speech signals. Further, a novel receive noise guard circuit means is used to discriminate between syllabic speech signals and high level noise transmissions from another station. The outputs of both the transmit and the receive noise guard circuit means are summed with the transmit and receive signals across unequal impedances to prevent seizure of the bistable control by ambient noise and to improve the receive channel sensitivity.