Do you have any insight into the source of those slowish
transmissions? A particular RTTY program or product? Or a particular
hardware device?
(1) The K3 paddle to RTTY mode where the user is not "leading" the
rig. (2) MMTTY where the user has set Char. Wait/Diddle Wait higher
than the very left edge of the slider. (3) MMTTY with "Limiting
Speed" - character pacing is 170 ms instead of 165 ms/stop bit is
~40 ms. (4) any software with Diddle = OFF and hand typing (most
users can't maintain 60 WPM).
IF I remember correctly, Joe W4TV write a summary about serial port
UARTs several years ago, describing the compromises inherent in
getting 45.45 baud FSK from a serial port. Perhaps Joe can refresh my
memory?
In my testing, a lot of UARTs appear to be generating 2 stop bits
instead of 1.5 stop bits. That, in addition to the Windows API which
forces integer baud rates which makes 45.45 into 45 baud.
It seems like 2Tone and GRITTY have "flywheels" that don't
necessarily wait for the start bit - this works well for full-speed
signals, but when the gap between stop and start bit is stretched it
doesn't work so well.
IIRC, G3YYD disables the "flywheel" if the stop bit is stretched. He
will need to confirm that.
73,
... Joe, W4TV
On 2015-04-27 10:43 AM, Larry Gauthier (K8UT) wrote:
Tim,
Thanks for sharing. I am particularly interested in your statement that
"MMTTY works better on "slowish RTTY" senders", which lends credence to
the notion that the best way to improve RTTY reception is to improve
RTTY transmission. Do you have any insight into the source of those
slowish transmissions? A particular RTTY program or product? Or a
particular hardware device?
IF I remember correctly, Joe W4TV write a summary about serial port
UARTs several years ago, describing the compromises inherent in getting
45.45 baud FSK from a serial port. Perhaps Joe can refresh my memory?
and, no - GRITTY would not decode BARTG75. I ended up with just 2tone
and MMTTY in that contest yesterday.
-larry (K8UT)
-----Original Message----- From: Tim Shoppa
Sent: Monday, April 27, 2015 10:02 AM
To: rtty@contesting.com
Subject: [RTTY] More GRITTY observations
Used three decoders in SP DX contest this past weekend. One each of MMTTY,
2Tone, and GRITTY.
The fabulous 15M openings to JA and YB we've had the past couple weeks in
my mornings, were a real treat.
The signals that 2Tone worked well on, GRITTY worked well on too. Hard to
pick a clear winner, glad to have all three up and in play. I especially
paid attention on weak signals.
I usually completely disable squelch in other simpler decoders but have not
really arrived at the right squelch setting for GRITTY. Probably I
shouldn't mess with it. Clearly there is some interaction between bandwidth
and GRITTY decoding squelch that I haven't quite gotten the feel of.
The dynamic range of the GRITTY waterfall is superb. It is good for
"Seeing" weak signals in the noise.
GRITTY AFC is superb. I hate hate hate MMTTY AFC, if I leave it on all the
time it wanders off to infinity. 2Tone AFC works well on longer
transmissions but with short contest exchanges it often doesn't have time
to keep up. GRITTY AFC was just superb for the off-frequency callers.
Correct me if I'm wrong, but it looks like it could "back-decode" after
switching AFC frequency.
I have noticed there are some "slowish RTTY" senders out there with odd
longer no-deedle idles between characters. MMTTY decodes these well, but
2Tone and GRITTY struggled with these. It seems like 2Tone and GRITTY have
"flywheels" that don't necessarily wait for the start bit - this works well
for full-speed signals, but when the gap between stop and start bit is
stretched it doesn't work so well.
I did succesfully adjust MMTTY and 2Tone for the 75 baud BARTG. I don't
think GRITTY supports 75 baud, but I've never been good at reading
documentation :-).
Tim N3QE
_______________________________________________
RTTY mailing list
RTTY@contesting.com
http://lists.contesting.com/mailman/listinfo/rtty
_______________________________________________
RTTY mailing list
RTTY@contesting.com
http://lists.contesting.com/mailman/listinfo/rtty
_______________________________________________
RTTY mailing list
RTTY@contesting.com
http://lists.contesting.com/mailman/listinfo/rtty
|