[Elecraft] K3: Odd ALC behavior

[Brian Hunt]

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

On 8/3/2017 13:25, Dave Cole wrote:
> Hi,
>
> I have an issue in  regards to obtaining 4 bars, and getting the 5th 
> bar of ALC to fluctuate while transmitting JT65.
>
> I have plenty of audio, and can drive the ALC to 6 or more bars if I 
> turn things up.  However, as I get to 4 bars with the 5th flashing a 
> bit, the ALC starts to fluctuate between nothing and 4 or 5 bars...
>
> That is to say, the ALC just goes to zero, no visible ALC, and then 
> teh ALC returns to 4 or 5 bars.  This happens across a one or two 
> second time span.
>
> The ALC is at zero more than it is above zero most of the time. If I 
> run it to five bars, with the fifth fluctuating, all is well, there 
> seems to be some sort of threshold at the 5th bar of ALC...
>
> I have tried a number of things to try and triage this...  For instance:
>
> 1.  Running in "Transmit Test" mode to eliminate RF feedback.
> 2.  Upping the audio level feeding the K3.
> 3.  Reducing the audio level feeding the K3.
> 4.  Upping the line in on the K3 setup.
> 5.  Reducing the Line in on the K3 setup.
> 6.  Adjustment of the WSJT-X output level control, under conditions 2 
> through 5 above.
>
> In all cases the above described behavior of the ALC dropping to zero 
> does not change in any way if I am at 5 or less bars.  That is to say, 
> if I take the ALC level to 4 bars, it starts dropping to zero more 
> than not...
>
> Does anyone have any suggestions as to what this might be?
>
> A a bit of history-- the computer and sound card were used on an Icom 
> 756 ProIII, and there was never an issue like this...  The ALC was 
> adjustable from zero to too much on the Icom, with no dropouts...
>