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

From: Ilia Mirkin
Subject: Re: [Discuss-gnuradio] Modem and/or ADSL Daughter card
Date: Wed, 10 May 2006 22:38:23 -0400
User-agent: Internet Messaging Program (IMP) H3 (4.0.3)

Quoting Michael Milner <address@hidden>:


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?


I'd like to mention that there are currently a number of soft modems out on the
market which occasionally have linux drivers for the audio portion. I don't
know the details of getting them to "pick up" the phone and such. Asterisk
(www.asterisk.org) has for a long time supported a card with the Intel IA-92
chipset. (I have one of these cards -- it worked OK, but not great esp with odd
phone line conditions, it could get confused as to whether it was on hook or
off, or whether the other side had hung up.) I believe that libtiff (or some
other unrelated-sounding library) implements V.34 (? the fax one) modulation. I
would guess that you can also use [AM]C97 modems to such an end, though I
haven't actually done that myself. Keep in mind that these cards are usually
designed for "FXO" signalling, i.e. they can't power other devices, and rely on
a line voltage to be supplied externally.

While you could use these cards for regular use (i.e. under the 64kbit ISDN
channel assumption), they of course can't be used for ADSL and the like, since
that uses a much higher frequency than the cards support.

(Not a USRP solution, but GNURadio could be made to work with these; I bet the
required interface is very similar to what Asterisk uses.)


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