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@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@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 ...
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