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

[Paul Stoetzer]

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 at 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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