[RTTY] GRITTY

[David G3YYD]

Bill

It has been done. First you use a synchronous format, which is exactly the
same for each and every transmission. Pity RTTY is asynchronous and the stop
bit length varies all over the place along with the actual baud rate sent.
If RTTY was always exactly 22millisecond for each bit and 33mS for the stop
bit then synchronous decoding could be used improving Character Error rate.

Then you add extra bits for FEC and interleave the bits over a few seconds
so an error burst is turned into single bit errors, which mean less FEC bits
need to be added. Then you send it a lot slower. However this would not be
practical to use as a chat mode nor for contesting. Many systems fail in
this area of not being very practical for chatting/contesting.

Then finally you persuade all guys currently using RTTY and PSK to use it...
Conclusion it isn't going to happen.

By the way G3PLX and I did exactly that in 1978 used a synchronous, bit
interleaved FEC system in 1978 of our own design. It worked well but an ARQ
system was better and also complied with a CCIR recommendation 476 you will
know it as AMTOR.

73 David G3YYD


-----Original Message-----
From: RTTY [mailto:rtty-bounces at contesting.com] On Behalf Of Bill Turner
Sent: 13 April 2015 01:12
To: RTTY Reflector
Subject: Re: [RTTY] GRITTY

------------ ORIGINAL MESSAGE ------------(may be snipped)

On Sun, 12 Apr 2015 12:50:38 -0400, you wrote:

>The true breakthrough in RTTY decoding will come when some smart 
>programmer

REPLY:

Or better yet, when some smart programmer comes up with a replacement for
RTTY that uses Forward Error Correction (FEC) and is equally fast, or nearly
so. Then all these multiple decoders will be a thing of the past, I hope.

There are plenty of FEC modes that ensure near perfect copy, but they are
painfully slow for contesting. There is one called Contestia but I don't
know of any contests using it so it hasn't really been evaluated by many
folks.  I have called CQ with it but never made a contact. 

Dream on. 

73, Bill W6WRT
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