[Elecraft] K3: Odd ALC behavior

[Brian Hunt]

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
>