DSP-TDD's: A new AMRAD project?

Richard Barth Richard.Barth@noaa.gov
Tue, 03 Aug 1999 13:09:29 -0400

I checked out the URL you provided.  V.18 (as mentioned there) is the 
standard number I was trying to think of and Omer Zak (who wrote that
web page) is the fellow I used to be in touch with.  I'll have to drop
him a note and say hello.  Since the page is 2 years old it's obviously
out of date and the version of V.18 he refers to there is probably not
the officlal one approved by ITU-T only last fall.  That one might be
available on the ITU site.



>Date: Tue, 03 Aug 1999 13:02:08 -0400
>To: Bob Bruhns <bbruhns@erols.com>
>From: Richard Barth <Richard.Barth@noaa.gov>
>Subject: Re: DSP-TDD's: A new AMRAD project?
>Bcc: rbarth, rbarth@tidalwave.net
>In-Reply-To: <37A63D2D.BB8C0565@erols.com>
>References: <>
>At 08:51 PM 8/2/99 -0400, you wrote:
>>I was only aware of 300 baud and 45.45 baud TDD standards, are there
>>more TDD specific modes now?  That would be a problem.
>The only TDD standard in this country uses 45.45 baud (60 wpm) Baudot.  
>300 baud is an ASCII standard, not a TDD standard.  The European standard
>is the same Baudot code, the same FSK tone pair, but a different baud rate.
>There is an international (ITU-T) standard of the V.* series (like V.34,
>V.90 etc.) that includes TDD capability.  I have not read it, but it
>presumably reflects accurately the tone pair used for TDD (1400/1800 Hz)
>and the U.S. and European baud rates.  It would, of course, also reflect
>current ASCII standards.
>>I guess the issue is to keep the advanced users capable of 56K, and yet
>>still capable of 45.45.  I think businesses would want standard products
>>for better manufacturer support (and modern operating speeds), but
>>individual users might accept ham help.
>>First thing to do is see what might be available now.  But it looks like
>>you did that and it's vaporware at present.    
>Actually, I haven't looked into what the industry is currently working on.
>As I mentioned, the newest standard (which I THINK is V.90, but I'm not
>sure) is fairly recent.  Given the speed at which industry incorporates
>new features aimed solely at the small deaf market, it may be a while 
>before the first modem meeting the new standard appears on the shelves.
>What my HEX correspondent was looking at was the use of provision methods,
>hacker-style, to make current DSP modems talk TDD rather than waiting for
>the manufacturers to modify their production lines or come up with a 
>software patch.
>>I found a site (http://www.weizmann.ac.il/deaf-info/tty_faq.html) where
>>several modems were identified which can run some form of TDD, if I
>>understand.  But this data may be dated, and the modems no longer
>Thanks for the tip; I'll check it out.  Some years ago I was in touch with
>a guy at Weizmann Institute who was trying to establish a new deaf comms
>network using ASCII.  He disappeared from my scope after a few years and I
>don't know whether he's still working on the project, but apparently Weizmann
>is.  I'll look.  
>>If the ITU approved a TDD encompasing standard, it might be available as
>>downloadable upgrades to some flashable modems.  Most of these are
>>manufactured overseas, but the flash-upgrades are available over the
>>What is that ITU standard, I'll see if I can find anybody supporting it.
>>  Bob, WA3WDR
>As I say, it's an ITU-T standard approved last fall.  I think it's V.90, but
>the correct answer should be on the ITU web page at http://WWW.ITU.CH
Richard Barth, W3HWN -- w3hwn@amrad.org -- Silver Spring, MD USA