[RTTY] BARTG 75 Sprint

[Joe Subich, W4TV]

 > Remember too that you are not comparing 7 to 5, you are comparing
 > 7+start+stop to 5+start+stop.

Actually 8+start+stop to 5+start+stop.  Since radio circuits are
probably more reliable with two stop bits we're actually talking
about 11/75 vs. 7.5/45.45 or 146.5 ms vs, 165 msec.

 > The biggest impediment though, as Bob K0RC pointed out is that MMTTY
 > lacks ASCII capability.

That may be true for AFSK but if MMTTY is opening a real UART at
75 8N2, the UART will be sending ASCII. It's a bit late to set up
a dummy load to dummy load test between MMTTY and cocoaModem to
find out for sure but I'll try to do that in the next day or so.

In any case, since Dave has the MMTTY source, I'm sure ASCII can
be added if it is not already supported.

73,

    ... Joe, W4TV

On 6/14/2010 2:26 AM, Kok Chen wrote:
>
> On Jun 13, 2010, at 10:10 PM, Joe Subich, W4TV wrote:
>
>> Even with the added bits the 8 bit code is slightly faster overall
>> (146 ms/character vs, 165 ms) than 5 bit/45.45 baud.
>
> I think I have mentioned earlier that 7-bit ASCII and 5-bit Baudot
> takes about equal duration to transmit a typical contest exchanges
> even when both of them use the *same* baud rate.
>
> Counterintuitive?  Perhaps.
>
> The reason is the ASCII exchange won't have to transmit the numerous
> FIGS and LTRS characters that you find in a Baudot exchange.  The
> Baudot exchange transmits shorter characters, but sends more of them.
> The ASCII exchange contains longer characters, but fewer of them
> since there are no LTRS or FIGS shift to send.
>
> With exchanges that contain numbers between spaces (or even a number
> in between alphabets of a callsign), the ASCII op actually spends
> less time sending a typical contest exchange.  With some other
> exchanges (e.g., if your callsign is RAEM and you use dashes between
> exchange numbers, such as 599-123-123) the Baudot op wins by a
> little.  Overall, I think it is a wash in terms of printed characters
> per second.
>
> Remember too that you are not comparing 7 to 5, you are comparing
> 7+start+stop to 5+start+stop.
>
> ASCII used to be transmitted at 110 baud, 7 bit + 2 stop, no parity
> and 170 Hz shift.  But you do not *need* to switch to 110 baud when
> using ASCII.
>
> The 110 baud number was probably determined by the then popular Model
> 33 Teletype.  (Just as the Model 19 drove the 45.45 baud number.)
> You certainly could keep using 45.45 baud or 75 baud as we do today
> with Baudot.  I personally think that 110 baud is needlessly fast for
> keyboard-to-keyboard QSO and rather wasteful of bandwidth and comes
> with an increase in error rate.
>
> The biggest impediment though, as Bob K0RC pointed out is that MMTTY
> lacks ASCII capability.
>
> 73 Chen, W7AY
>
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