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DC impedance auto phone patch line interface circuit

2015-01-18 11:02  
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A telephone line interface circuit for connecting telephone equipment provided with internal speech lines having predetermined DC  impedance to external telephone lines, comprising a rectifying circuit connected with the telephone lines for rectifying the DC voltage coming from the telephone lines; a dial pulse sending circuit which makes connection and disconnection between the output terminals of the rectifying circuit and the internal speech lines for sending dial pulses to the telephone lines; and a polarity inversion detecting circuit which discriminates th evoltage relationship between the telephone lines and the internal speech lines for detecting the polarity inversion of the DC voltage coming from the telephone lines.This circuit provides for the receiver-to-phone line and phone line-to-transmitter link with both using an op amp for gain.An autopatch, sometimes called a phone patch, is a feature of anamateur radio(or other type oftwo-way radio)repeaterorbase stationto access an outgoingtelephoneconnection.Userswith atransceivercapable of producingtouch tones DTMF  signals) can make atelephone call, typically limited by settings in the autopatch module to be only totoll-freenumbers, such aslocal callsortoll-free numbers. The term phone patch more accurately describes a system that is dialed and connected by a user manually operating a base station, which was more common before computer technology made automation of the process easier.
Autopatch telephone line interface