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I've confirmed a number of times using a number of professional spectrum
analyzers that the signal generator is putting out what the knobs indicate. The
non-linearity is not due to the HP8648C. My personal "target" for the
non-linearity would be in order: 1) VB Cable and 2) SkyPipe.

I can test SkyPipe as I did the HP8648C, but VB Cable has no hooks other than
links between applications within the PC. Possibly Jim Sky could comment on the
linearity of SkyPipe?

I well realize the difference between white noise cal and my single signal
tests. But either will expose non-linearities in the system. I have a known
professional noise generator source which I could use which I used to calibrate
the old RJ setup which employed only Radio SkyPips. That was far easier and
quite intuitive. Personally I am not a fan of judging colors. No two pairs of
human eyes view subtle color differences and/or intensities identically. But
they sure make pleasing and attractive plots. Just my two-cents.

Any additional suggestions as to how best to sleuth the non-linearities I exposed?

I have an SDRPlay RSP1. Early on with our experiments with those at LTO (Little
Thompson Observatory), here at home for me and Terry's (Dr. Terrance Bullette)
experiments, we sadly discovered it was sorely prone to IMD and overload.
That's why at LTO (and personally) we collectively placed the SDRPlay products
on the shelf where they still reside. I've only recently obtained an RX-888
MKII, but, man, does it eat the 5-vdc power like a Class A amplifier at L-Band!

Dave - W?LEV



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On Thu, May 22, 2025 at 2:00?AM Larry Dodd via groups.io <>
<101science@... <mailto:[email protected]>> wrote:

Dave
The non-linearity isn’t in SDR Console for sure. You’re using a single
frequency stepped calibration where we use Jim Sky’s stepped wide band noise
calibrator spanning ~8 MHz. If you have a known calibrated power meter you
could check your HP output. That would help to tell you where the
non-linearity lies.
Larry

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On Wed, May 21, 2025 at 9:48?PM W0LEV via groups.io <>
<davearea51a@... <mailto:[email protected]>> wrote:

I was intrigued by the calibration of the standard RJ setup. While I do
not use that setup, I decided to measure what I use for other purposes,
including RJ. So, have a read of the attachment. I'm using the AirSpy
Discovery HF+ to test the linearity. The system is diagrammed to start
and then, I ran an HP generator up by 10 dB steps ultimately into Radio
SkyPipe. I was somewhat disappointed at the non-linear behavior of the
system. Please have a read of the attachment.

CONCLUSION: Yes, calibration is needed if linear response to the input
is required!!!

Dave - W?LEV*
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*Dave - W?LEV
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