Alan,
That is getting into issues associated with WSJT-X and FT8.
My website article is written to apply to all soundcard data modes and
not FT8 specifically. There was no intention for addressing all the
various data modes that could be used. All of them require the right
amount of audio drive.
You should look to the FT8 forums for questions about that aliasing. If
it were a K3 problem, that aliasing would also be happening with other
data modes as well.
Other soundcard data modes do not have a problem with a TUNE at 1000 Hz,
so why is FT8 any different?
Of course, if your soundcard is generating harmonics or significant IMD
before it reaches the K3, there is not much one can do other than
getting a different soundcard.
I don't know about the "moving 10kHz" thing, but I have heard reports of
similar symptoms.
73,
Don W3FPR
On 5/13/2018 4:22 PM, G3XAQ wrote:
Don,
I suggest you need to draw attention in your web page and general advice on
here to the requirement to choose the AUDIO FREQUENCY with some care when
setting up ALC for FT8 via the TUNE button in WSJT-X.
The problem seems to be that the DSP sampling rate inside the K3 must not be
related to the TUNE frequency. Ideally I expect they should be co-prime, or
something like that, to avoid aliasing artifacts in the ALC bargraph
readout. The actual frequency you should choose is probably affected by PC
and K3 clock frequency accuracy becasue a change of just a few Hertz can
have a dramatic effect.
In my case, the default WSJT-X tune frequency of 1000Hz is about as bad as
you can get. My ALC bargraph oscillates with a beat frequency of not much
more than 1Hz. And the ALC goes from zero to 6 bars! What is really
confusing is that WSJT-X leaves the tune frequency at whatever it was when
you last transmitted, so if you tune around, click on some signals, have a
listen and then try using TUNE the audio frequency could be anywhere unless
you take specific action.
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