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-----Original Message-----
From: pat.9a...@gmail.com
To: fr...@fkirschner.net, wsjt-devel@lists.sourceforge.net
Sent: 2019-01-03 11:42:29 AM
Subject: Re: [wsjt-devel] Using WSJT-X Decoding Technique with RTTY
Hi Frank,
You can try to download 2Tone for RTTY.
So far best decoder was made for MSDOS by K6STI Bitty and Ritty. That was better than any Windows or so RTTY software nowdays.
Best 73
Patrik 9A5CW
Datuma čet, 3. sij 2019. 17:14 Frank Kirschner <frank.kirsch...@gmail.com piše:
Hi, Bill,Thanks for your reply.I wasn't suggesting a change to the standard for RTTY, which, of course, would be impossible at this point. I was pointing out that the software I have used to decode RTTY is nowhere close to the theoretical limit, or even the hardware discriminator I built years ago. DM780 and MMTTY, the two programs I remember using, require very high signal to noise ratios to provide even moderately good decoding.Do you have a recommendation on software that might perform better than what I am using?I first used RTTY in the late 1960s, when I had my home-brew TU and a Kleinschmidt teleprinter, so I'm familiar with the electro-mechanical technology for which Baudot code was designed. I designed a weather collection network for Thailand in the early 1970s that used mechanical teleprinters and prepared tape messages. It was a bit of a kluge, but it worked for years.73,FrankKF6E_______________________________________________On Thu, Jan 3, 2019 at 10:52 AM Bill Somerville <g4...@classdesign.com> wrote:On 03/01/2019 15:33, Frank Kirschner wrote:
> Many years ago, I had a home-brew RTTY TU. It had two 88 mH torroids
> in the tuned circuits and a differential amplifier as a detector.
> Occasionally, the received signal would fade below the noise, but the
> Kleinschmidt teleprinter would keep printing the decoded text. I have
> tried several current software packages for decoding RTTY signals, and
> all of them require quite strong signals to decode at all, and very
> strong signals to provide 100% print.
>
> I was wondering if the decoding method used in WSJT-X for FT8 could be
> ported to a RTTY decoder. I realize that FT8 has a lower symbol rate,
> which provides more time to integrate, and incorporates redundancy,
> which improves accuracy. But the theoretical lower limit for decoding
> RTTY is something like -5 dB S/N, and the current programs are nowhere
> near that.
>
> If RTTY facilities could be integrated with WSJT-X, not only would the
> decoding be better, but the log scanning functions of WSJT-X and
> JTAlert would be better, significantly improving contest operation.
>
> I confess I haven't looked at the decoding techniques used by RTTY
> software, but I suspect, based on performance, that it could be improved.
>
> 73,
> Frank
> KF6E
>
Hi Frank,
this is well covered ground, some existing Baudot decoders have very
good performance with built in weak and fading signal models to optimize
them.
The techniques used to decode FT8 are based around a block message
format that includes parity bits and checksums for advanced forward
error detection and correction, Baudot is a character based stream code
with no forward error correction capability. RTTY was designed for an
era where automation was mechanical and quite limited, just having a
code that could be used to modulate a transmitter and be printed by a
receiver was about the sum of the technical design. RTTY's *only*
similarity with FT8 is that it is a frequency shift keyed constant
amplitude signal. Even the simplest addition of a single parity bit to
detect, but not correct, single bit errors would need a fundamental
non-backwards compatible change to the Baudot code.
73
Bill
G4WJS.
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