Re: [Discuss-gnuradio] Fax question

[Tim Pozar]

On Tue, Jan 21, 2003 at 10:17:19PM -0800, Eric Blossom wrote:
> On Wed, Jan 22, 2003 at 12:39:17PM +1100, David wrote:
> > I have been looking at GNU Radio and was wondering how feasible it might be
> >  to use it for something like a fax protocol analyser.
> 
> Definitely.  Most fax modems only sample at 7200 or 8000 samples / second.
> 
> > I would be looking at using either baseband analogue POTS or aLaw/uLaw. I
> > looked over the source and seem to remember seeing a uLaw implementation.
> 
> Assuming you're trying to listen to a real phone line, your quickest
> approach is probably to capacitivly couple tip and ring to the sound
> card input.  This is a slight simplification, you'll want some kind of
> zener's to clamp any high level input (e.g. Ring, 200V P-P), but it's
> no big deal.

>From an early post of mine... :-)

Tim
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From: address@hidden (Tim Pozar)
Newsgroups: mod.telecom
Subject: Re: Connecting a phone line to a stereo
Message-ID: <address@hidden>
Date: Wed, 26-Nov-86 20:50:56 EST
Article-I.D.: ucbvax.8611270640.AA06603
Posted: Wed Nov 26 20:50:56 1986
Date-Received: Thu, 27-Nov-86 06:47:38 EST
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>Can anyone give me a circuit for connecting a phone line to broadcast
>over a stereo system?  

    The circiut can be made very easliy out of two .1uf disk caps, and a 
10k to 600 ohm tranformer.  WARNING!  This circuit is not FCC accepted.  
   Ahem, now that I said that...  Just hook it up to the red and green wires
on the block.  The caps are to block DC to the transformer and prevent the 
Telco equipment from seeing a "off-hook" status.  In order to keep the line 
up, you should put a 1k resistor across the red and green wires.  You could 
even put a switch in series to act like a switch hook.

          .1uf
  Green __| |____    _________\  To consumer level/impeadence 
          | |    )||(         /         audio source
Telco       600  )||(  10K
          .1uf   )||(
    Red __| |____)||(_________\
          | |              |  /
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