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

[Joe Subich, W4TV]

 > The Baud rate, Mark/Space shifts are text fields for each (Baudot and
 > ASCII) interface and you can use any reasonable number, such as 45.45
 > baud or 110 baud. I.e., you can run Baudot RTTY at 110 baud and ASCII
 > RTTY at 45.45 baud if you wanted to.  Or 23 baud ASCII, if you like.

OK, I was looking in the wrong place ... expected to find data rate in
Preferences rather than "Aux".

 > I do not used fldigi, but if memory serves, it has only has one RTTY
 > interface.  However, the number of data bits is selectable and when
 > you change the data bits to 7 or 8, it will switch to using ASCII
 > (ITA-5) or extended ASCII encoding.  I do not know if you can choose
 > 45.45 baud with ASCII, but I suspect that you can.

Yes, one can choose 45.45 baud with ASCII.  However, choosing ITA-5
requires using the "custom" setting for RTTY - there is no separate
"ASCII" operating mode.

 > I believe someone has told me at one time that MMTTY can also choose
 > 7 bits of data.  However, MMTTY keeps using Baudot encoding (together
 > with FIGS and LTRS) by stuffing extra zeros into the most significant
 > 2 bits (gulp).  This is not first hand knowledge, so someone else
 > will need to confirm whether MMTTY can run ASCII as is.

MMTTY appears to be able to transmit ITA-5 (7N2) at 45.45 baud.  At
least I can configure it that way and what I transmit can be copied
by cocoaModem's ASCII receiver when the baud rate is set to 45.45.

Any move to 45.45 baud ASCII would be much easier with an improvement
in MMTTY's interface (the ability to not reset to 5 bit on the "HAM"
button).  In addition, neither Ham Radio Deluxe (DM780) or MixW appear
to support ASCII and that would be an impediment to adoption.

73,

    ... Joe, W4TV



On 6/28/2012 1:19 AM, Kok Chen wrote:
>
> On Jun 27, 2012, at 9:39 PM, Joe Subich, W4TV wrote:
>
>> Does cocoaModem provide a way to set the data rate for ASCII down
>> to 45.45 baud?
>
> cocoaModem has duplicate wideband 2-receiver RTTY interfaces.  One
> uses Baudot encoding and the other uses ASCII encodings.  You can
> select either interface dynamically.
>
> The Baudot interface is restricted to 5 bits data, with stop bits
> selectable between 1, 1.5 or 2 bits.
>
> The ASCII interface can use either 7 or 8 data bits (7 bits is more
> "standard," the 8 bit encoding uses the standard Extended ASCII).
> With stop bits again selectable as 1, 1.5 or 2 bits.
>
> The Baud rate, Mark/Space shifts are text fields for each (Baudot and
> ASCII) interface and you can use any reasonable number, such as 45.45
> baud or 110 baud. I.e., you can run Baudot RTTY at 110 baud and ASCII
> RTTY at 45.45 baud if you wanted to.  Or 23 baud ASCII, if you like.
>
> I do not used fldigi, but if memory serves, it has only has one RTTY
> interface.  However, the number of data bits is selectable and when
> you change the data bits to 7 or 8, it will switch to using ASCII
> (ITA-5) or extended ASCII encoding.  I do not know if you can choose
> 45.45 baud with ASCII, but I suspect that you can.
>
> MultiPSK can also choose between 7- or 8-bit ASCII but with a fixed
> 110 baud rate.
>
> I believe someone has told me at one time that MMTTY can also choose
> 7 bits of data.  However, MMTTY keeps using Baudot encoding (together
> with FIGS and LTRS) by stuffing extra zeros into the most significant
> 2 bits (gulp).  This is not first hand knowledge, so someone else
> will need to confirm whether MMTTY can run ASCII as is.
>
>> Why 110 baud?  There is a significant bandwidth and s/n penalty in
>> the higher speed even if the shift were held constant at 170 Hz.
>
> Short answer: Model 33 and Model 35 Teletype machines.
>
> Back in them days, the 14, 19 and 32 can only do 45.45 baud Baudot
> (unless you swap out the gears), and the 33 and the 35 can only do
> 110 baud ASCII.  There was a popular model 28, but I draw a blank on
> what baud rate it handles.  If I had to guess it would be 110 baud
> since early DEC computers used them (I don't think any modern
> computer used Baudot).
>
> When TNCs implemented RTTY and ASCII, they defaulted to what the
> teletype machines used; thus 45.45 Baudot, 110 baud ASCII.  Today,
> with software modems, your baud rate is only limited by the 300 baud
> upper limit that the FCC limits a US ham to (below 10m).  I don't
> think there has been a lower baud rate limit, so you should be able
> to use 45.45 baud ASCII as long as your software modem allows it.
>
> 73 Chen, W7AY
>
>
>