[RTTY] RTTY spectrum analysis article

[Robert Chudek - K0RC]

Hello Andy...

Wow! An excellent article with a lot of detailed work you (and others) 
put into this analysis. It really should be published in a magazine(s) 
with a world-wide audience. I agree that the ARRL lab should add this 
analysis to the transceiver reviews they are publishing.

Of course the 'data junkie' in me wants to see a compilation of all the 
radios that have been manufactured in the past 10 or 20 years! Along the 
lines of the Sherwood Engineering RX Test Data: 
http://www.sherweng.com/table.html

Your analysis certainly brings to light that when using internally 
generated FSK, there is little option for the operator to 'narrow up' 
their spectrum if necessary, short of tearing into the TX chain and 
patching in additional filtering. Maybe this will spur an aftermarket, 
similar to the roofing filter kits that sprang onto the market a few 
years ago.

Thanks for sharing this!

73 de Bob - KØRC in MN

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On 1/9/2013 8:39 PM, aflowers at frontiernet.net wrote:
>   
> Fellow RTTY operators,
>   
> I had some interesting private emails about the spectra I posted here, especially about the now infamous "Signal 3".  If you haven't seen Signal 3, you might want to look at it, it's rather important for what's coming:
>   
> http://www.frontiernet.net/~aflowers/rtty_examples/
>   
> A few people asked whether I had contacted this station about the problem.  I suppose there was a problem, as this station was clicking over 3 KHz of my receiver.  The answer is that I did not I did not contact this station. I had no reason to.because I am fully aware of the response I would get. (Truth be told, the owner of Signal 3 is gracious enough that he would move mountains to improve things.  He's one of those guys that if you tell him he's QRMing you he will actually move without talking back.  But for now his signal makes a better object lesson.)
>   
> The fundamental causes of Signal in #3 or any of the "wide" signals in those plots fundamentally has *nothing* to do with AFSK vs. FSK keying.  It does however have everything to do with the waveform coming out of the radio.  This does however offer up what is going to be a bitter pill for many of us:  Signal 3 is representative of the "true" FSK generator in every modern radio of which I am aware.  If you run "true FSK" and are loud, this is most likely what you look like when the band is open (and no, you do not have the "cleanest signal on the band" at any signal-to-noise ratio).
>   
> No, this doesn't necessarily mean you should give
> up "true" FSK keying. There are things you can do about it, and some
> people are people taking responsibility and doing these things--please read the
> article! Then let's talk about it because I don't have all the answers.
>   
> You can find the article here:
>   
> http://www.frontiernet.net/~aflowers/k3rtty/k3rtty.html
>   
> Respectfully,
>   
> Andy Flowers, K0SM/2
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