RE: [WriteLog] AFSK on RTTY not LSB on 1000mp field

[George Johnson <w1zt@comcast.net>]

Thor,
Your comments and experience are quite interesting.  Yes, there are "key 
clicks" associated with FSK.  I use AFSK with the RITTY program by 
K6STI.  That program switches tones at the zero degree phase crossing of 
the audio signal and eliminates the sharp edge.  I have made spectrum 
observations similar to your description.

As in CW, the key clicks are most bothersome when a strong station is 
operating very close in frequency.  I can usually tell which stations are 
probably using FSK vs AFSK when I listen for the keying sideband 
energy.  The audio effect is more pronounced during multipath or 
backscatter signal conditions.  And it seems to cause more difficulty in 
decoding compared to the softer keying.

I had not considered a correlation of FSK with the known FT1000MP CW keying 
problem but the effect on the signal sidebands is very similar.  Thanks for 
your observation and I plan to take a little closer look at the energy 
spectrum of the various signals.
73, George .. W1ZT

At 09:25 AM 2/19/2004, Þorvaldur Stefánsson wrote:
> I decided to try my own advice and switch to AFSK and it does´nt work as I
> thought it should.
>
> I could have sworn I had afsk working under 'user mode' but it doesn´t.
>
> My apologies to all for my wrong advice.
>
> I now use PKT (lsb) menu 6-4 (Packet Frequency Display Offset) is 2125 and I
> changed menu 6-5 to 2210 Hz (center of 2125/2295).
>
> That gives me access to the filters using the Packet rear panel jack as
> S55OO and others have found.
>
> The reason I have gone to AFSK rather than FSK is that I am now using a
> Frederick 1280A which has a "True FSK"
>
> ("as defined by FEC's patent, which allows the change from mark to space to
> be made as a smooth progression of intermedita frequencies directly related
> to the selected keying rate.  This reduces side band enerby normally
> produced by the nearly instantaneous change from mark to space associated
> with the more commonly used FEK technique")
>
> - I fed the AFSK output into my spectrum analyzer program and switched to
> "True FSK" and the difference is dramatic - much cleaner.  I wonder if some
> rigs have "key clicks" on RTTY (FSK mode) as well as on CW?
>
> 73
>
> Thor, TF3MM
>
>
>
>
> The treachery of a friend is worse than that of a foe.
> -Gísla Saga Súrssonar


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