Re: [Discuss-gnuradio] Modem and/or ADSL Daughter card

[Eric Blossom]

On Thu, May 04, 2006 at 02:01:31PM -0400, Michael Milner wrote:
> Hello,
> 
> I was just wondering if anyone has used GNURadio for any non-radio
> applications, specifically phone line modulation/demodulation.
> 
> It shouldn't be too difficult to design a daughter board for the USRP to
> sample phone line voltage (with an appropriate line interface circuit of
> course).  After that it should be rather easy in GNURadio to generate DTMF
> tones for dialing, and modem tones for data communication.
> 
> Any thoughts?
> Mike

A simple DAA (Data Access Arrangement) plus the LF daughterboard would
probably work.  There are two chip DAA's available.  Been a while
since I looked, but I think that Crystal Semiconductor used to make
them.  Google "solid state daa" There's also the classic Midcom
transformer plus a couple of other discretes.  These things are tricky
to get right.  You definitely want to find somebody's reference design
and use that.  Or use the pre-approved chipset.

The USRP is pretty much thermonuclear overkill for this application.
You could just use a sound card with a DAA.  That's how all the
"soft-modems" work.  IIRC some of the the AC97 codecs support a second
channel for telecom (modem) apps.

Eric