Re: SDR-Console Power dBm Accuracy


jdow
 

You are best sticking with all noise or all signal. And you need to calculate precisely what bandwidth is represented by each pixel on the spectrum analyzer screen AND how each pixel finds its way into the running power average. Noise compared to noise does not have this problem. Signal compared to signal faces typical SINAD issues.

TANSTAAFL

{o.o}

On 20210623 22:15:18, Larry Dodd wrote:
Jdow
Yes agree. I think you have it described well. The Mark 1 eyeball you described isn’t highly accurate at averaging the bouncing line. A steady tone and step attenuator would be more accurate. Will do some more thinking on this. Thanks. 
Larry, K4LED 

On Jun 23, 2021, at 11:47 PM, jdow <jdow@...> wrote:

 Hot and cold noise sources are useful. Depending on the amplifier pure liquid nitrogen may be a good friend for accuracy. If you can pull in a precise calibrated step attenuator and nice hot noise source it might be interesting to see what you get as you add in attenuation. And ideally you'd work with a long term RMS average on the noise. (I think Simon does that on his spectrum.) Generally a Mark 1 human eyeball is not a very good tool to read spectrum analyzer noise levels.

An S-Meter is pretty poisonous to use with noise readings. But you might discover it can give you some useful readings when deltas are involved. If I had to do it I'd probably take some tools I already have and doctor them to do the precise job that's needed = set a precise IF bandwidth and measure and long term average the I^2 + Q^2 noise level coming out of the IF filter. I do not know that any tool already made out there caters to this. And I have spent over 3/4 century learning how to be lazy when faced with this sort of issue.

{^_-}

On 20210623 18:57:21, Larry Dodd wrote:
jdow,
Thanks. We use a calibrated on/off noise source to do a Y Factor Method for SDR noise figure measurements. I have found just using the spectrum dBm measurements easier than the dBm meter. It usually reads -140 dBm constantly with low noise floors. 
Thanks,
Larry

On Jun 23, 2021, at 9:49 PM, jdow <jdow@...> wrote:

 That's a big subject.

To a first approximation the spectrum is very accurate for differences in reading. It's theoretically perfect if there is a perfect A/D converter involved. The A/D converter's step to step linearity can mess up this theoretically perfect relative calibration.

In any absolute sense any calibration present is rather loosy goosy unless you provide a precision source and take care getting your readings. Otherwise "loosy goosy" can mean +/- 20 dB or worse.

I refuse to address Simon's S-Meter accuracy until I check to see if I can still spoof it.

{^_^}

On 20210623 17:53:16, Larry Dodd wrote:
I have been asked the question, "How accurate are the SDR-Console dBm spectrograph and dBm meter readings?"  Can anyone answer that question? We are interested in measuring the noise floor of various SDR receivers.
Thanks,
Larry, K4LED



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