OOK ... I still have an ATU-1000 here run in parallel with the soundcard at
times. Nice buttons on the front panel that choose between mark and space,
mark only or space only. I bet some folks here didn't even know it was
possible!
73,
John GW4SKA
----- Original Message -----
From: "Kok Chen" <chen@mac.com>
To: "RTTY Reflector" <rtty@contesting.com>
Cc: "Rex Maner" <k7qq@netzero.net>
Sent: Monday, September 17, 2012 11:25 PM
Subject: Re: [RTTY] AFSK to FSK converter
On Sep 17, 2012, at 2:20 PM, Rex Maner wrote:
I don't understand any of this ""OOK"" or such stuff.
OOK is described in communications textbooks as On-Off Keying. You can
see it mentioned here, for example,
http://en.wikipedia.org/wiki/On-off_keying
With OOK, the presence of a tone represents a Mark and the absence of a
tone represents a Space (or vice versa, for inverted signal).
Think of it as what we know as "CW" and indeed, the original amateur RTTY
ops had used OOK to send signals between their teleprinters. Feld
Hellschreiber is another mode that uses OOK (but it is really more of a
facsimile mode than a digital mode)
A second complementary tone is added to the single OOK tone to form 2-tone
FSK. Some digital modes use even more tones; DominoEX uses 18 tone FSK,
for example.
FSK works much better than OOK for HF because of fading (the two tones
automatically establish the threshold level for the ones and zeros even as
the signal fades up and down), and especially for selective fading, when
you can still copy a single tone (as an OOK signal) after the other tone
has faded under the noise.
If you have used Mark-only or Space-only reception with an ST-8000 (or
ST-6000), you would have experienced OOK copy. Some software modems
implement it too. I know of one for sure, but I only use one digital mode
program and don't know for sure how many others have Mark-only or
Space-only receive capability.
By the way, Mark-only and Space-only is almost a lost art nowadays. If
they are not already doing it, more software modems should implement it.
There are numerous times when I can copy through QRM that is clobbering
one FSK tone by using Mark-only or Space-only to decode the surviving
tone.
The reason OOK transmission is bandied about here is that one can convert
the on and off audio tones from a sound card into an FSK keying signal
even when the single tone is moving around.
There are two software modems that I know for sure can transmit OOK. But
the implementation of OOK is rather trivial -- if the software author
knows how to generate an AFSK signal, it is child's play for him to
generate an OOK signal. Programs that don't implement OOK transmission
probably are that way because there has been no justification for it.
73
Chen, W7AY
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