[GreenKeys] Diddle, Real Metal, 1.0 Stop Pulse

[Jerry]

Surprisingly enough I recall some 30+ years ago when Bill Carver 
(k6olg/w7aaz now) and Jim Haynes (w6jve) and I think Larry Laitinen 
(wa6jyj/w7jyj) were running a lot of tests on RTTY using just a 1.0 stop 
pulse.  All of us were using model 28 machines as I recall.  The model 
28's ran 'real busy' when receiving the 1.0 stop pulse and sounded like 
they were going much faster than the 60wpm normal speed using a 1.42 
stop pulse.

What was really amazing was the copy was noticeably better.  Now that I 
think about it, I seem to recall that Bill (k6olg/w7aaz) had designed a 
new TU and it was processing the info much better with the 1.0 stop 
pulse and a full set of diddles.  These tests were run over some period 
of time on several occations, and the copy was always much better.

I just went out and looked in my 'stash' and yep, I still have my 
original lash up of Bill's TU sitting on a shelf.  I guess a true 
'rtty'er never gets rid of anything, chuckle!

Jer -n6jp-

----- Original Message ----- 
From: "Bob Camp" <ham at cq.nu>
To: "Veenstra, Lester" <Lester.Veenstra at intelsatgeneral.com>; "Greenkeys 
((E-mail))" <greenkeys at mailman.qth.net>
Cc: "Jerry" <gh1lockett at bak.rr.com>
Sent: Friday, February 25, 2005 6:16 AM
Subject: Re: [GreenKeys] Diddle, Real Metal, & Indeterminate Line Length


: Hi
:
: You are correct at least as far as the machines I have really dug into
: (15's). The mechanical felt pad clutch engages at the end of a 1.0
: length stop pulse. The only problem with this is that it (as least 
from
: 20 year old memory) is a full 1.0 length pulse. If the sending machine
: is running just a bit fast the receiving machine will fall out of
: synchronization every so often.
:
: As far as I can see there is no advantage to diddle on a mechanical
: TTY. There certainly is an advantage on certain types of TU's but not
: on the TTY it's self. If anything diddle wears out the machine a bit
: faster.
:
: The biggest problem I see with "synthetic sync" operation using diddle
: is that you do not have a defined stop bit length. Normal clock and
: data recovery circuits rely very much on the fact that they know
: exactly what they are looking for. Each weird stop bit length (1.31,
: 1.42, 1.5) effectively is a different clock rate you have to watch 
for.
: I have never seen a sync system that uses odd width pulses in the bit
: stream.
:
: This isn't to say you can't watch for all the possible rates and guess
: which one is being used. The issue is that you can guess wrong if you
: have  three closely spaced stop pulse widths. If you really want to go
: wild you can always go to a Veterbi decoder and do convolutional guess
: work until you run out of CPU clock cycles. I suspect that at 45 baud
: that a lot of of bits (> 2 characters) . It would still work better if
: you knew the stop pulse width ahead of time since you would have fewer
: buckets to examine and less chance of error.
:
: We're getting a bit far afield from my original intention here which
: was simply to caution about the use of 1.0 length stop bits if there's
: a mechanical TTY on the other end ...
:
: Take Care!
:
: Bob Camp
: KB8TQ