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| SSA2021X - 20 dB attenuator sufficient? |
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| fourfathom:
--- Quote from: pdenisowski on February 09, 2024, 05:04:00 pm --- --- Quote from: fourfathom on February 09, 2024, 08:01:17 am ---In many cases an "overload" indication doesn't mean a damaging-level input, but just that the input level with the current attenuation and gain settings results in a signal that is causing the detector to clip or distort. It's not an input power problem, just a dynamic range problem that can be corrected by adjusting the attenuation or gain settings. No harm done. --- End quote --- Yes, exactly this. In fact, often I've seen what is clearly distortion caused by an overdriven input even BEFORE any kind of "overload" indication appears. --- End quote --- Yes. The active stages of a spectrum analyzer will always distort, but it isn't until this distortion exceeds the measurement noise floor that you notice it. There is compression, leading to clipping -- that is usually obvious and the analyzer may warn you about it. But there is also intermodulation distortion that shows up as sum and difference mixing products. And in newer gear there are sampling artifacts. If you don't understand these you can reach some very wrong conclusions about what the analyzer is showing you. |
| fnaumann:
--- Quote from: tautech on February 09, 2024, 03:35:14 am ---As yet we have not seen any screenshots from you showing settings that might trigger warnings. FYI max continuous signal is specified as: 30 dBm, 3 minutes, fc ≥10 MHz, att > 20 dBm, preamp off --- End quote --- I used a simple 10 MHz sine wave signal with 1 to 5 dBm output level (SDG 50 ohm output mode). 30 dB attenuator (10 W) plus DC blocker was connected externally upstream of the SSA. In the SSA, the internal attenuator was deactivated in the "Amplitude" menu (set manually to 0dB) and the trigger for the overload warnings was the activation of the internal preamplifier (Preamp = On). Of course, I didn't have time (and the motivation) to take a screenshot when the warning signal sounded. And I don't want to consciously reproduce these overload situations in order to produce screenshots for the forum. --- Quote from: tautech on February 09, 2024, 03:35:14 am ---As yet I prefer to control any instrument rather than let an Autotune process second guess my requirements therefore I have never used it, maybe I should get some experience with it. :-// --- End quote --- I also prefer to set my measuring instruments myself. Only when nothing works (no useful signal is shown) at all do I occasionally press "Autoset" on my Owon Oszilloskops to check whether there is even a displayable signal. On the other hand, I used the "Auto Tune" on the SSA 3021X Plus more often because the signals displayed look ugly via manual settings and didn't really get any better even after a lot of tweaking. With the TinySA Ultra, on the other hand, the user can see all the relevant signals without having to strain too much. And the TinySA Ultra also has complex setting options. Considering the large display and the very good operating concept of the Siglent SSA, the signals displayed are disappointing for me as a beginner. Or my expectations are too high and unrealistic. I'm going to look into my spectrum analyzer in more detail, simply because the thing was so expensive ... |
| fnaumann:
--- Quote from: blackdog on February 05, 2024, 10:36:29 am ---Your 10dB attenuator attenuates the power 10x, with a 20dB attenuator it is 100x, but it may be if you were to use a 20dB attenuator that the signals you want to see disappear into the noise. The point is, that you work "wisely", better to work with -20dB first, see if you can make sensible measurements, too much in the noise, then if you do not see very strong signals, use the -10dB attenuator. --- End quote --- I usually start with a 30 dB attenuator. I suspect that due to my overprotecting use of attenuators, the signals on the SSA2021X Pro are so weak that the signal-to-noise ratio is relatively low and therefore the display of the signals is suboptimal. |
| tautech:
--- Quote from: fnaumann on February 10, 2024, 01:06:24 pm --- --- Quote from: blackdog on February 05, 2024, 10:36:29 am ---Your 10dB attenuator attenuates the power 10x, with a 20dB attenuator it is 100x, but it may be if you were to use a 20dB attenuator that the signals you want to see disappear into the noise. The point is, that you work "wisely", better to work with -20dB first, see if you can make sensible measurements, too much in the noise, then if you do not see very strong signals, use the -10dB attenuator. --- End quote --- I usually start with a 30 dB attenuator. I suspect that due to my overprotecting use of attenuators, the signals on the SSA2021X Pro are so weak that the signal-to-noise ratio is relatively low and therefore the display of the signals is suboptimal. --- End quote --- Here is where you need to wind down the RBW and those faint signals will magically rise from the noise floor. ;) Leave RBW/VBW at 1:1 for now. The penalty is Sweeps will take longer however that can also be addressed by narrowing the sweep. A good place to pick up some SSA tips/tricks is in the SSA3021X thread and posts from rf-loop starting from here: https://www.eevblog.com/forum/testgear/siglent-ssa3000x-spectrum-analyzers/msg958295/#msg958295 |
| fnaumann:
compare TiniSA Ultra vs. SSA2021X Plus Test signal: simple 10 MHz sine wave signal with 0 dBm output level (Siglent SDG1032X in 50 ohm output mode) External attenuation: 20dB plus DC blocker CF: 10MHz Span: 1MHz RBW: 10KHz (and below for SSA2021X Plus) With the TinySA Ultra, the noise floor is below -70 dBm at 10 kHz RBW and there is a clear demarcation between signal and the noise floor. For the SSA2021X Plus with the same RBW value, there is (for me) no clear limit (from -75 dBm to -50 dBm) where the noise floor ends and the actual 10 MHz signal begins. |
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