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.
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On 20210623 22:15:18, Larry Dodd wrote:
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.
On Jun 23, 2021, at 11:47 PM, jdow
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
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.
On Jun 23, 2021, at 9:49 PM, jdow
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
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.