Here's some followup:
FLDIGI shows the "pumping" affect with carrier tones of 500, 1000, 1500,
and 2000 Hz.
WSJT-X 1.8 shows the "pumping" affect with carrier tones of 1000, 1500
and 2000 Hz (couldn't select 500 Hz).
The affect is very narrow with frequency. 10 Hz either way and the
output and ALC display and MON output is rock solid. Changing the K3
filter center frequency has no effect on the above.
73,
Brian, K0DTJ
On 8/4/2017 10:58, Brian Hunt wrote:
I spent some quality time with my K3, FLDIGI and an oscilloscope
today. I had the same problem as described. Looking at my USB
soundcard output to the K3, the amplitude of the audio from FLDIGI in
TUNE mode was rock solid. Looking at the MON output from the K3, the
level oscillated in time with the ALC "pumping" at about 2.4 Hz (timed
with a stop watch). At the same time the K3 power output into a dummy
load was rock solid at a selected 10 watts.
Then I changed the carrier frequency in FLDIGI slightly off 1500 Hz
and the "pumping" went away! At 1515 Hz I could easily set the ALC to
the desired 4 bars solid, 5th flickering. Then I remembered (and
verified) that the default filter center in DATA A mode is 1500 Hz. I
changed the filter center frequency to 1450 Hz and moved the FLDIGI
frequency around but couldn't reproduce the "pumping".
I plan to repeat the same tests with WSJT-X 1.8 but wanted to get this
out to the group.
73,
Brian, K0DTJ
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