Alan,
How high is the input level to the K3 Line IN? I am wondering if you
are driving the transformers in the audio in slightly into saturation.
Try lowering the soundcard output and increasing the LINE gain.
73,
Don W3FPR
On 5/14/2018 3:05 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.
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