[RTTY] Why 45.45 baud?

[Joe Subich, W4TV]

> I should point out that many amateurs today actually use send at 45
> baud due to the serial ports used for radio FSK keying being in many
> cases unable to send at 45.45 baud (22mS bit length).

It is not that the UART (serial port) is not capable of operation at
45.45 baud - the rel issue is that the serial port API in Windows can
only set *integer* baud rates (the parameter is type integer!).  If
one has a hardware driver that aliases 45 (or 46) baud to 45.45 baud
the UART generally functions correctly at that rate.

 > They also often have stop lengths that jitter as well.

Jitter is a more complex issue ... many of the hardware drivers (board
specific DLLs) seem to set only 1 or 2 but not 1.5 stop bits.  The
bigger problem appears to be due to a combination of software like
MMTTY which, when set to pace data uses 7.8 bits per character instead
of slightly *less than* 7.5 bits, and the slot based nature of USB
which causes data to arrive at the USB UART "bursts".

73,

    ... Joe, W4TV


On 4/16/2014 4:59 AM, David G3YYD wrote:
> I always thought that the reason 45.45 was used in North America was because
> that is what the commercial land line used. The machines when sold as
> surplus were then used for amateur radio RTTY. QED 45.45 became the NA (i.e.
> USA) norm.
>
> In Europe the machines used commercially ran at 50 baud. So when amateurs
> started to use RTTY in Europe in the 50s and 60s EU used 50 baud rate.
> Unfortunately 45.45 and 50 baud machines do not work one another. Over time
> due to the numbers of RTTY operators being so much larger in USA the 45.45
> baud became the worldwide standard. Those of us in EU changed the motor
> speed on our teleprinters to run at 45.45.
>
> The machine I used in the early 70s was a Creed 7E/RP which had a mechanical
> governor which was easy to alter to 45.45 baud. Some machines however used
> synchronous motors and they needed a gear change.
>
> In retrospect the use of 45.45 was the correct choice as in poor conditions
> it will/does have lower character error rate than 50.
>
> I should point out that many amateurs today actually use send at 45 baud due
> to the serial ports used for radio FSK keying being in many cases unable to
> send at 45.45 baud (22mS bit length). They also often have stop lengths that
> jitter as well.
>
> 73 David G3YYD
>
> -----Original Message-----
> From: RTTY [mailto:rtty-bounces at contesting.com] On Behalf Of Kai
> Sent: 15 April 2014 22:03
> To: Peter Laws
> Cc: RTTY contest group
> Subject: Re: [RTTY] Why 45.45 baud?
>
> Peter,
> Hoff, K8DKC, also includes snippets about FCC regs regarding RTTY. You can
> follow why we are where we are with the FCC.
>
> I learned RTTY in the last 5 years from that series, this reflector, and the
> MMTTY reflector.
> RTTY has a very rich and interesting history history!
>
> 73
> Kai
>
> On 4/15/2014 4:51 PM, Peter Laws wrote:
>> On Tue, Apr 15, 2014 at 2:14 PM, Kai<k.siwiak at ieee.org>  wrote:
>>> Dennis,
>>> Great question!
>>>
>>> See the second installment of RTTY articles by Irvin Hoff, K8DKC,
>>> "Operating the Teleprinter",  QST, Feb 1965, pp 29-35. He wrote 13
> articles
>>> in QST in 1965-66 on all aspects of RTTY.   the reciprocal of
> 45.454545...
>>> baud (we round to 45.45, some EUs use 45 baud)  equals 22 mS, the
>>> basic timing interval for the teletype code. He also discusses the
>>> roots of 1, 1.5, 1.43, 2 pulse stop bit intervals.
>>>
>>> The series is very interesting reading, and traces the archaic roots
>>> from land-line tone units today's RF amateur-RTTY standard.
>>>
>>
>> Can't say as I'll read them all but I pulled this one from the archive
>> and it's pretty interesting.  About to read about USOS ...
>>
>>
> _______________________________________________
> RTTY mailing list
> RTTY at contesting.com
> http://lists.contesting.com/mailman/listinfo/rtty
>
> _______________________________________________
> RTTY mailing list
> RTTY at contesting.com
> http://lists.contesting.com/mailman/listinfo/rtty
>