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Spectrum analyzer in a high traffic strong signal environment

 

There might be cases where a spectrum analyzer is used to measure a particular signal that is surrounded by many adjacent strong signals. Perhaps the signal measured isn't as strong as the adjacent signals and requires and increase in level but unfortunately the adjacent signals are raised as well.

Although none of the strong adjacent signals are overpowering of the analyzer, perhaps they are all somewhere around -30dBm but there are about 10 of them or more, is it possible that although the input levels look fine on screen when in reality the analyzer is actually seeing higher than -30dB at it's input thus staying below the input level limits might not always be so obvious.

Thoughts on this, thanks
Lothar baier
 

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If the signals are radiated then using cables and adapters with very good shielding can help mitigate the issues but if they are conducted than things become difficult!



On Mar 2, 2022, at 11:23, DW via groups.io <wilson2115@...> wrote:

?There might be cases where a spectrum analyzer is used to measure a particular signal that is surrounded by many adjacent strong signals. Perhaps the signal measured isn't as strong as the adjacent signals and requires and increase in level but unfortunately the adjacent signals are raised as well.

Although none of the strong adjacent signals are overpowering of the analyzer, perhaps they are all somewhere around -30dBm but there are about 10 of them or more, is it possible that although the input levels look fine on screen when in reality the analyzer is actually seeing higher than -30dB at it's input thus staying below the input level limits might not always be so obvious.

Thoughts on this, thanks

 

"...is it possible that although the input levels look fine on screen when in reality the analyzer is actually seeing higher than -30dB at it's input..."
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Not only is it possible, it is very probable.? Before connecting a spectrum analyzer to any antenna, I like to connect the antenna to an RF power meter.? The broadband sensor will measure the total RF energy that will be incident on your spectrum analyzer's mixer.

In most cases, I believe it is necessary to use some sort of preselector to narrow the spectrum to the area of interest.? I have a complete set of K&L tunable preselectors covering the range from 80 MHz to 1 GHz.? Each covers an octave band.

K_L Filter 2.JPG

 

Thanks,

I have to confess this happened to me recently with a spectrum analyzer. Currently it seems to work fine where the -10dB calibrator shows -10dB on the display.

Is there ways which I might assess the health of the input to the spectrum analyzer if I might have actually hurt something? Thanks

Ops!
 

If the analyzer shows the correct level from the calibrator - it's probably fine.? If your instrument requires you to connect a jumper between the calibrator output and the RF input - that is an even higher confidence.

For a more comprehensive verification, connect your signal generator to the spectrum analyzer and measure various frequencies and amplitudes.

When measuring signals in a high RF environment, if you suspect mixer overload, increase the input attenuation.? If the suspect signals decrease by more that the extra attenuation, they were bogus.

Also, most analyzers won't reduce attenuation below 10 dB without extra steps.? That protects the instrument because attenuators aren't as easy to damage (or as expensive) as mixers are.? Zero dB attenuation can give you the most sensitivity for viewing weak signals - but - don't go there unless you are sure it is safe.

0 - Generator field calibration.jpg

 

Another measure is to look at the level of the LO feed through at "0" frequency. Usually expected to be less than -20 dB (that is what I see on 8566 SA)


Cheers!

Bruce

Quoting nj902 <wb0emu@...>:

If the analyzer shows the correct level from the calibrator - it's probably fine.? If your instrument requires you to connect a jumper between the calibrator output and the RF input - that is an even higher confidence.

For a more comprehensive verification, connect your signal generator to the spectrum analyzer and measure various frequencies and amplitudes.

When measuring signals in a high RF environment, if you suspect mixer overload, increase the input attenuation.? If the suspect signals decrease by more that the extra attenuation, they were bogus.

Also, most analyzers won't reduce attenuation below 10 dB without extra steps.? That protects the instrument because attenuators aren't as easy to damage (or as expensive) as mixers are.? Zero dB attenuation can give you the most sensitivity for viewing weak signals - but - don't go there unless you are sure it is safe.
 

Hi:

You might switch in some attenuation and see if all the peaks fall by that amount.

--
Have Fun,

Brooke Clarke, N6GCE

axioms:
1. The extent to which you can fix or improve something will be limited by how well you understand how it works.
2. Everybody, with no exceptions, holds false beliefs.
 

Great responses, thanks!

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