[GreenKeys] TU for Computer

Fri Jan 11 10:12:42 EST 2019

Hi all,

After a few hours of tinkering, I was able to decode the sample WAV file on the w1hkj.com site at:

Page: http://www.w1hkj.com/modes/index.htm
File: http://www.w1hkj.com/modes/Baudot45-170.wav

The decoded text comes out as "NOW IS THE TIME FOR ALL" 😊

The code uses an integer implementation of the Goertzel Algorithm originally written by Poul-Henning Kamp <phk at freebsd.org> to decode DTMF tones. It's very robust, and I've been using it for 20 years for VoIP applications.

The next step would be to clean the code up to allow specifying the mark and space frequencies, and then connect it up to a sound card driver. It could then be tested with a real-time audio stream from somewhere.

If there is any interest, I'd be happy to keep tinkering. I can also put the code up on BitBucket if anyone is interested.  

The actual output from the program is below:

filename: Baudot45-170.wav
sample rate:8000
samples:  39948
channels: 1
data: 1f LTRS
data: 0c N
data: 18 O
data: 13 W
data: 1f LTRS
data: 04 SPC
data: 06 I
data: 05 S
data: 1f LTRS
data: 04 SPC
data: 10 T
data: 14 H
data: 01 E
data: 1f LTRS
data: 04 SPC
data: 10 T
data: 06 I
data: 1c M
data: 01 E
data: 1f LTRS
data: 04 SPC
data: 0d F
data: 18 O
data: 0a R
data: 1f LTRS
data: 04 SPC
data: 03 A
data: 12 L
data: 12 L

Craig Southeren                
Post Increment Consulting and Software
craigs at postincrement.com
www.postincrement.com
US: +1 415 800 4201
Mobile: +61 417231046 

-----Original Message-----
From: Craig Southeren <craig at postincrement.com> 
Sent: Friday, 11 January 2019 2:14 PM
To: Jim Haynes <jhhaynes at earthlink.net>
Cc: W7HPW Radio <W7HPW at outlook.com>; greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] TU for Computer

My background is in VoIP, and I’ve spent a lot of hours working with software fax demodulators and modulators. There are quite a few of these as open source. Most work to 4800 baud, and some even do 9600 baud.

Modding one of these to do baudot FSK at 50 baud would be fairly simple. I might be interested in doing this if someone can provide a sample audio file

BTW: my first computer used a model 15 teletype for I/O. One of these days I’ll find get another noisy green monster so I can show my kids and grand kids what the past was really like

Sent from my iPhone

> On 11 Jan 2019, at 13:35, Jim Haynes <jhhaynes at earthlink.net> wrote:
> 
> Yes and no.  Of course you are aware of all the computer software that 
> turns the computer into a complete RTTY terminal, but I think what you 
> are asking is for software that replaces the demodulator with digital 
> signal processing so you can drive a TTY machine with the Baudot output.
> 
> The earliest DSP software was K6STI's RITTY program.  I talked him 
> into providing a cleaned-up Baudot output when it was receiving, but 
> didn't ask him to provide for a TTY keyboard input.  The story of that 
> software is that it ran under DOS, required a certain kind of 
> SoundBlaster sound card, and was rather expensive.  He pulled it off 
> the market because it was being pirated, and also never ported it to 
> anything beyond DOS and a more generic sound system.  I think he said 
> it was not possible to do that and maintain the performance it gave.
> 
> I shouldn't say that was the earliest - there was probably some using 
> a dedicated DSP engine, but K6STIs was the first to use a PC that I 
> know of.  And you didn't find many Pentium computers running DOS even 
> back then.
> 
> I think I was told that MMTTY has a Baudot output, but that may not be 
> true and I haven't looked.
> 
> I've begged Dave W1HKJ to add a Baudot output to fldigi but apparently 
> that is either not possible or is not a high priority.  Maybe if more 
> of us begged for it he would do it.  It is open source, so maybe 
> somebody else could do it.
> 
> You don't want just an ST-6 equivalent in software; you really want 
> regenerated Baudot to go to the printer.  Because there is something 
> like a 15dB disadvantage to Start-Stop TTY signals caused by the 
> mechanical selector in the machine.
> 
> What some people currently consider the best software demodulator is 
> 2Tone, which does not run standalone but runs under N1MM Logger.  It 
> is free but closed source.  I don't know if one could figure out how 
> to use the 2Tone module with his own wrapper to make it function as a 
> simple demodulator.
> 
> Jim W6JVE
> 
> 
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