[RTTY] AFSK to FSK converter

[John GW4SKA]

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 at mac.com>
To: "RTTY Reflector" <rtty at contesting.com>
Cc: "Rex Maner" <k7qq at 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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