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Old 12-Sep-2020, 11:41 PM   #48
Retired A/V Tech
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,677
Originally Posted by tripelo View Post
When you have the scanners them properly adjusted, have you seen any spurs in either scanner?
There appears to be spurs in all three of my scanners, but it's not unexpected in equipment that isn't lab grade. I would need a pure source to really tell the spurs from actual signals.

The RTL-SDR dongle has a lot of spurs when I put a 75 ohm termination resistor on the front end, but they are minimized when signals are measured.

I think the Spectrum Spy scanner for the R2 is a lot cleaner than the RSP Spectrum Analyzer for the RSP1A.

Your images and videos are informative.

Good to see a comparison of both scanners displays.
Thank you. I was curious to make the comparison myself.
Reading the scale looks like about 60+ dB dynamic range displaying those particular signals.
A 12 bit ADC should be able to do at least a 60 dB dynamic range.
Have you checked the accuracy of the dB scale?
The dB scales on my three SDRs are relative, not absolute. There is one exception, the calibration of the RSP1A with the SDRuno software is calibrated under certain conditions:

SDRplay RSP2 for accurate RF power Measurement

This is my test of the SDRplay calibration:

I have used that feature to measure the strength of TV signals, but a correction factor of about +14 dB is needed:

Measuring TV Signal Strength with an SDR

Is there a means in software to calibrate the dB scale against a reference?
I think there are offset adjustments for the relative scale, but I haven't hunted for them because the position of the signal changes with adjustments of gain and display.

I think the calibration feature of the SDRuno mentioned above is fixed in the hardware or firmware.

Wonder, when calibrated at one or two points, if it maintains some accuracy over a larger range of dB?
I have not tested the linearity of the relative dB scales. The accuracy of the "use under certain conditions" calibration of the SDRuno with RSP1A SDR appears to hold well over a wide range.
Do you think one of the two scanners could be more accurate than the other?
I don't think the relative scales of either one could be considered "accurate" with so many stages in series.
If you can not measure it, you can not improve it.
Lord Kelvin, 1883
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