[RTTY] The Problem with AFSK ...

[John Merrill]

Do K3s key click using FSKD or 590s using FSK?

John N1JM


On Sat, Jan 19, 2013 at 12:43 PM, Kok Chen <chen at mac.com> wrote:

>
> On Jan 19, 2013, at 10:51 AM, Joe Subich, W4TV wrote:
>
> > Doesn't mean a thing if the level going into the mic jack is
> > already too high for the microphone preamplifier.
>
> This is why I always advised against using the mic input for AFSK.  By the
> time you saturate the mic pre-amp, it is game over.  You are most likely to
> present a non-symmetrical signal to the balanced modulator, and we know
> what that does.
>
> The other, less obvious (but equally important) reason is this: the cable
> between the sound card and the radio now has to carry a tiny signal.  This
> means that any noise and hum pickup is much larger by proportion.
>
> To do good AFSK, send as large a signal as possible on the cable to the
> radio and if needed, add two resistors to attenuate it at the radio itself.
>  But be sure not to saturate any transformer that is in the large signal.
>
> On something like the Elecraft K3, as example, use as large a line level
> in the menu as your sound card will deliver cleanly.  Typically, I have
> found that -3 dB of the sound card full scale output is a good value to
> use.  You then adjust the line level menu in the rig to accept that.  Only
> back off the sound card output if that is still too much for the line level
> menu to compensate.
>
> Even on something like the Kenwood TS-590 with its built in sound card,
> you should still use a good sized signal from the modem, just in case there
> is ground noise within the rig itself.
>
> It is really not hard to produce good AFSK, as Andy K0SM's spectrum
> captures showed.  All those clean AFSK signals in Andy's spectra showed
> that it is not just theoretical possible, but it is quite practical to
> produce pleasant AFSK RTTY signals that are friendly to neighbors.  And
> quite a few contesters are using it.  With something like a K3 or a TS-590,
> there is almost no reason not to.
>
> Like I have personally discussed with a few folks, the problem with FSK
> keyclicks is that we have to wait for the manufacturers to get off their
> behinds and do something about it (just look at how long it took Yaesu to
> remove CW keyclicks from their contest grade rigs).  It is not going to
> happen overnight, even though it is really simple to accomplish for rigs
> that generate FSK signals in their DSP stages.  In the meantime, we already
> have means today to generate a clean signal instead of waiting on
> manufacturers.  With CW keyclicks, responsible people also took matters in
> their own hands and modified the FT-1000s and other rigs to make them
> acceptable.
>
> 73
> Chen, W7AY
>
>
>
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