grnberg@mit-caf.MIT.EDU (David R. Greenberg) (12/20/90)
Hello there, 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? Thanks in advance for your help. - David Greenberg Dept. EECS MIT
jon_sree@world.std.com (Jon Sreekanth) (12/21/90)
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.comgrayt@Software.Mitel.COM (Tom Gray) (12/21/90)
>The 'official' specs are maintained by Bellcore. You'll want section 6 >(and possibly others) of the LSSGR The official spec's in North America are maintained by ANSI. BellCore has input to these spec's but so does the rest of the industry. Whole sections of the US are supplied with telephone service which follows the REA spec and not the LSSGR. The LSSGR also does not specify customer premises equipment. The days of the AT&T monopoly are over