Transceiver with noise immune voice operated transmission/reception switch

摘要

A mobile transmitter receiver intended for simplex radio communication via a base station with another mobile transmitter receiver, the mobiles being intended for use in vehicles, has a microphone 1 connected to envelope detectors 3 and 4. The latter receive the same signal A, but detector 3 has faster time constants than detector 4, so that the envelope B produced as output is representative not only of speech signals but also of noise signals in the vehicle. The envelope detector 4 is slower acting and does not respond to normal speech signals and consequently only represents the slower varying vehicle noise. When these signals are subtracted from each other an envelope D representative substantially only of speech is produced. This output can be used to trigger the mobile into transmit mode, and permits hands-free operation in a vehicle environment. IMAGE