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Re: [RTTY] PSK31 is faster (Was FD RTTY Question)

To: Kok Chen <chen@mac.com>
Subject: Re: [RTTY] PSK31 is faster (Was FD RTTY Question)
From: Paul Stoetzer <n8hm@arrl.net>
Date: Wed, 27 Jun 2012 16:43:24 -0400
List-post: <rtty@contesting.com">mailto:rtty@contesting.com>
Somebody should set up an ASCII contest. That would be interesting.

Paul, N8HM

On Wed, Jun 27, 2012 at 4:36 PM, Kok Chen <chen@mac.com> wrote:
>
> On Jun 27, 2012, at 12:47 PM, Alex Malyava wrote:
>
>> Why don't we just invent/introduce some new RTTY standard -
>> the one with 6 bits instead of 5 - covering whole alphabet and digits
>> without any FIGS/LTRS and speed it up a little bit to compensate an extra
>> bit?
>
> There is no need to introduce another "mode du jour" even.
>
> 7-bit ASCII (CCITT ITA-5) RTTY has been FCC approved (see part 97.309(c)) for 
> a long time now.  fldigi supports it, so does MultiPSK and cocoaModem, among 
> others.
>
> In a discussion (a year or even longer ago) on this reflector, I had shown 
> that for most RTTY contest exchanges, ASCII RTTY beats out Baudot RTTY in 
> speed, even when both are running 45.45 baud.
>
> You get rid of the FIGS/LTRS confusion (thus problem with USOS 
> incompatibility either; USOS is a Baudot problem), allows lower case, and it 
> still beats out Baudot in contesting speed.  It is when sending paragraphs of 
> upper case text that Baudot wins over ASCII.
>
> Because of the Teletype Models 33/35, the popular speeds for running ASCII 
> RTTY was 110 baud.  At that speed, it will wipe the floor with Baudot RTTY.
>
>> Or drop one stop bit to save the length? Or use 3 frequency FSK -
>> shift left is "0", shift right is "1" and middle is sync/start/stop ?
>
> 3FSK may not be a good idea.  The reason is that the equalizer to compensate 
> for selective fading will be at best very complex to build.
>
> 2FSK has the very unique ability to fight selective fading with a very simple 
> thresholding scheme.  Once you add more tones, you can no longer build simple 
> ATC circuits.
>
> For that reason, you will find that there is nothing in MFSK16 (16 tones), 
> DominoEX (18 tones) or Olivia that explicitly fixes the selective fade 
> problem -- they all use long interleaved codes to fight QSB in general -- and 
> you may not want to use long interleavers with short contest exchanges; the 
> latency will need to be over 1 second to be effective.  You will need to add 
> latency to the exchange time.  Selective fading happens quite often.  You can 
> almost not avoid it with a Rayleigh path.
>
> Anyhow, the solution is already at your fingertips, and the FCC has blessed 
> it for years now.  It is called ASCII.  And 110 baud with 170 Hz shift is a 
> breeze.
>
> 73
> Chen, W7AY
>
>
>
>
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