[Elecraft] K3: Odd ALC behavior

[Joe Subich, W4TV]

On 8/5/2017 11:14 AM, Wes Stewart wrote:
> But IMHO, you need to put a 30 dB attenuator on the input of the 
> internal sound card; it is way too sensitive. I'm having to run the 
> Windows gain at less than 5% and Line In at 10 or less.

Actually, you need to adjust the options in the Windows *.inf file
used for the PCM-series CODEC (or use the codec that identifies as
line level).  Windows is turning on a 20 dB preamp in the CODEC.

I suspect if one sets the Windows Sound Options (Control Panel) to
display dB rather than percentage, the minimum level will be some-
thing like 16 to 20 dB!  That indicated the fixed 20 dB "mic preamp"
is engaged.

73,

    ... Joe, W4TV


On 8/5/2017 11:14 AM, Wes Stewart wrote:
> Wayne,
> 
> There are no beat notes. These frequencies, at least from the FT8 
> program in Tune mode are single frequency.  Based upon output RF 
> spectrum measurements*, with for example 1010 Hz input and 4-5 bars of 
> ALC, I see spurious or intermodulation sidebands, down -65 dBc.  If I 
> change nothing else but adjust the tone frequency to 1000 Hz  the 
> spectrum is the same but the ALC bars are cyclic, going from none to 
> 4-5, at about the 2 HZ rate Brian reported earlier. (Slow ALC in 
> action?)  That's the good news.
> 
> If I set the tone to 1500 Hz, the FT8 mid-band target, I'm presented 
> with the cyclic ALC and some ~193 Hz, -50 dBc sidebands.
> 
> I have tried this with both the K3S internal sound card and via Line 
> In/Out into my laptop sound card.  The results are more-or-less the 
> same.  But IMHO, you need to put a 30 dB attenuator on the input of the 
> internal sound card; it is way too sensitive.  I'm having to run the 
> Windows gain at less than 5% and Line In at 10 or less.
> 
> I would suggest that you do some measurements with a low-distortion sine 
> wave audio source run into the radio to eliminate the possibility that 
> this junk is a result of all of the digitally generated tones.
> 
> If this (what I will call a) problem continues to exist then I think a 
> fix is in order.  Expecting users to select particular frequencies to 
> use to set gain levels isn't an acceptable workaround.
> 
> Regards,
> 
> Wes  N7WS
> 
> 
> * My "spectrum analyzer" is my SDR-IQ which I have used to measure TX 
> IMD on both my K3 and K3S.  Your IMD
>   measurements on my K3S concurred with mine within 1 dB or less.
> 
> On 8/4/2017 4:45 PM, Wayne Burdick wrote:
>> Is it possible that a beat note between tones (and their harmonics) is 
>> what’s modulating the ALC reading? If so, moving the tone slightly off 
>> the standard pitch may be an acceptable workaround.
>>
>> Wayne
>> N6KR
>>
>>
>>> On Aug 4, 2017, at 1:42 PM, Wes Stewart<wes_n7ws at triconet.org>  wrote:
>>>
>>> Good find Brian!!! I see it too in FT8.
>>>
>>> This probably explains the great variability in results reported. 
>>> Some of us have a problem, others say, Huh, what the heck are you 
>>> talking about?
>>>
>>> Wes, N7WS
>>>
>>>
>>> On 8/4/2017 11:33 AM, Brian Hunt wrote:
>>>> 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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