http://elecraft.85.s1.nabble.com/K3-Odd-ALC-behavior-tp7633052p7633127.html
> internal sound card; it is way too sensitive. I'm having to run the
line level). Windows is turning on a 20 dB preamp in the CODEC.
... Joe, W4TV
> 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<
[hidden email]> 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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