I use spectrum analyzer N9040B. And there was a need to measure SNR using spectrum analyzer. Please help me solve this problem. Thanks.
Below is an acquired signal.
Don't know if you have already resolved this, this is an old post. The responses you are seeing could be generated in many ways. They could be spurious responses, residuals, or a combination of either. They could also be generated by a mismatched source whereby the source is generating the products. To help isolate the cause, there are several things you can try.
1. Set the unit up to duplicate your issue. While observing the issue displayed in the picture, try increasing the internal attenuator by 10 dB. If the signal remains in place and noise floor rises up, your log amp is working and the analyzer will still show the level as -5.07, but the noise floor will be higher. At the same time, if the markers at 1 and 3 remain the same, this usually indicates the source as causing the issue, not the spectrum analyzer. If the responses disappear or decrease, the signal is causing distortion at the front end of the spectrum analyzer. This may be because the source you are using does not have a good match at the front end of the spectrum analyzer, or the spectrum analyzer has high distortion at the input mixer. I see you do not have the preamp on, this eliminates that as the culprit.
2. Remove the input signal. If the responses are still there, these are residuals. This could indicate a problem with the analyzer. If the responses disappear when the input signal is removed, either the analyzer is creating distortion signals (usually at the first mixer) or the signal is causing the distortion due to a mismatch.
3. Put another attenuator in line with your source to give it more isolation.(Directivity) Then change the reference level to -10 dBm. If the spurious responses go down and the signal still gives the correct indication, your source may be causing your issues. If the spurs reappear at the same level, the analyzer may be causing the issues.
4. Lastly, make sure you are using a good cable. Even though this is low frequency, a bad cable can cause all kinds of issues at low levels.
Hope this helps,
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