The problem was discussed in this thread last year.
http://elecraft.365791.n2.nabble.com/K3-Odd-ALC-behavior-td7633052i20.html
Gordon - N1MGO
On 05/14/2018 03:05 AM, Alan Ibbetson wrote:
Don,
I'm puzzled you when you say
"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"
I can reproduce this problem with my K3 with MMVARI on other data
modes. I have tried it with another PC and sound card and again I can
still see the problem. So I suspect that feeding a pure sine wave from
any source into LINE IN can cause ALC bargraph artefacts at certain
specific audio frequencies.
This is not FT8 specific, nor is it audio harmonics or IMD. It is
simply an unfortunate choice of audio tone frequency interacting with
the K3 internals. Or at least that is my best guess from the evidence
I see here. The only constant throughout these tests is my K3. If it
is faulty then OK, no big deal.
I hoped by reporting this effect on this mailing list I might help the
others who have also commented about it. If there is a consensus that
it's specific to my setup then OK. I can reliably avoid my problem by
changing the audio tone frequency just a few Hz so I will just do that
and get on with my life.
73, Alan G3XAQ
On 13/05/2018 23:20, Don Wilhelm wrote:
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.
--
Gordon - N1MGO
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