Thanks Brian.

I've been reviewing my test setup. Because of limited USB ports on my normal station computer (laptop) I have been using a new (to me) desktop I'm building to be the station computer, to run both WSJT-X and my SDR-IQ software (SpectraVue) for this investigation. The sidebands I mentioned are quite noticeable but it started to not make sense to me in the way they moved as I changed the tone frequency.

To eliminate possible crosstalk between programs I went back to the laptop running WSJT and used my other K3 as a manually tuned spectrum analyzer. The sidebands are still there but way down in the mud. I think I'm hearing what's being generated in the SDR-IQ but I have yet to prove that, or understand why they might be generated. It's not overload, the main signal and sidebands change amplitude dB per dB in sync with a stepped attenuator on the input. And as I said elsewhere, when I was suffering TX IMD issues this same receiver was used to document the problem and when the radio went back to Elecraft for mods, they agreed with my numbers.

That said I decided to check calibration on the SDR-IQ while running on the new computer. A lot of the processing is done in the SDR-IQ so I didn't expect an issue other than tweaking FFT gain in the SpectraVue program. I connected the XG2 and tuned it in on 14.06 MHz. The trace was jumping in amplitude about 3-4 dB at about a 1 Hz rate. I also run Lady Heather via a serial port to a Motorola Oncore timing receiver (1PPS) and I've seen it take over my mouse before, making it jump all over the screen. So I disconnected the serial port without effect. I rebooted and started only SpectraVue and saw the same issue.

One last experiment (for now) was to use a third computer to run the SDR-IQ. On this one everything is perfectly stable. So I have a baffling problem with one computer, unfortunately the one I was using to present earlier data, which are of course now suspect.

Nevertheless, the cyclic ALC is still there and the difficulty in setting levels is too.

Frankly, I don't know why I'm doing all of this for a mode that I don't even 



On 8/5/2017 2:47 PM, Brian Hunt wrote:
Not seeing your -50 dBc side bands. Maybe there is a little blip at -68 dBc. 
Pic below is WSJT-X FT8 @ 1500 Hz with 100 Hz/division, BW 10 Hz. The old scope 
is pretty drifty at those numbers. 😄
I'll add it to my photo site.

Brian, K0DTJ

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