🚀 go-pugleaf

In article <5510@mit-caf.MIT.EDU> grnberg@mit-caf.MIT.EDU (David R. Greenberg) writes:

   I realize that this may be a very common question, but I haven't read this
   bulletin board for some time now.  Could somebody please post the
   specifications for a standard phone line jack i.e. what the various voltages
   are on the four wires during various phases of phone operation?


When the phone is on hook (open circuit), the voltage is -48V DC. 
The connection upto your house is usually modelled as a 48V battery 
in series with  0.4 - 2 K ohm of DC resistance. When you pick up the 
phone (make it go off hook), your phone has 200 to 600 ohm of DC 
resistance. In terms of AC impedences, the phone wire is usually 
considered to be a 600 ohm load. The signal power on the line is 
usually referenced to 1 mW through a 600 ohm load ( 0 dBm is 
0.775 V of signal). DTMF signalling is around - 6 dBm, voice is 
a little below this. 

Ringing is nominally 20 Hz, 90 VAC superimposed on the 48V battery. 
Ring voltage stops when the phone goes off hook. 

All these numbers are from memory, and they're all nominal (I've found
various books disagreeing on these 'nominal' values). The good part is
that the system works well with a wide range of values. Most common 
telephones can be rung with as little as 40 VAC of ring voltage, and 
don't need 48V DC bias. 

The 'official' specs are maintained by Bellcore. You'll want section 6
(and possibly others) of the LSSGR 

/ Jon Sreekanth

Assabet Valley Microsystems			Fax and PC products
346 Lincoln St #722, Marlboro, MA 01752		508-562-0722
jon_sree@world.std.com