All of the below is nominally correct. Unfortunately you will find quite a
bit of variation in the real world, especially on PBX and key systems used
in businesses.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

----- Original Message -----
From: Dan Michaels <oricom@LYNX.SNI.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Friday, August 18, 2000 9:55 PM
Subject: Re: [PIC]: Modulated pulses


> Igor Pokorny wrote:
> >Hello all:
> >
> >I would like to get any help how to find a busy signal on telephone line
by
> >a PIC knowing exactly neither the modulation frequency nor the length of
> >pulses.
> >Could someone tell me where to look for a theory or some example?
> >
>
>
> I think most of the following are correct:
>
> US TP SYSTEM
> ============
> D.C. Line Voltage (Talk Battery) - 48v with receiver on-hook, red wire
> (ring) negative, 5v for off-hook (with 50-1000 ohm d.c. load on line).
>
> Ring Signal - 20-90 vp-p, at 20-40 hz.
>
> Dialtone - dual 345 and 440 hz sinewaves.
>
> DTMF Tones - 1 high-band plus 1 low-band sinewave at frequencies shown in
> DTMF Table, at max transmission level of 0 dBm averaged over 3 sec (approx
> 24.5v RMS), for minimum of 50 msec duration and 45 msec interdigit time.
>
> Busy Signal - dual 480 and 620 hz sinewaves, 0.5 sec on, 0.5 sec off.
>
> Ringback Signal (simulates phone being rung up) - dual 440 and 480 hz
> sinewaves, 2 sec on, 4 sec off.
>
> Receiver Off-Hook Tone (when someone forgets to hang up the phone) - quad
> 1400, 2060, 2450, and 2600 hz tones, pulsed at a 5 hz rate.
>
> Speech Signals - 200 - 3400 hz, bandlimited.
> ======================
>
>
> I also have an appnote that shows a number of these signals on
> a scope display:
>
> AN-PTB04 - Telephone System Testing Using the PTB
>
> http://www.sni.net/~oricom/appnotes.htm
>
> best regards,
> - Dan Michaels
> Oricom Technologies
> ===================
>
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