SSA2021X - 20 dB attenuator sufficient?

[fourfathom]

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.

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.

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]

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

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.

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. 

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]

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.

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]

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.

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.

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.

[markone]

I'm also interested to this topic being the owner of a Siglent SSA3021X-TG and I have a simple and clear question :

what is the input power limit that guarantees that the instrument will not be damaged with ANY possible instrument setting ?

In my opinion this number should be available on the instrument datasheet.

I'm in the process to select a set of  attenuators in order to analyze the power output of some HAM radios, of course trying to keep the balance between instrument safety and S/N ratio, but I'm now understanding that is not an easy task 

[RoV]

SSA3021X ? 

[hpw]

I liked to measured the freq-. response of my wide-band 20..40dB amplifier.

So the tracking gen., as a maximal of a maximal of 20dB attenuation supported, I did run into into an input level overdraft.
This is IMHO a very hard limitation/restriction.

So it required, to attenuate the tracking generator, to more than the allowed maximal of 20dB.

hp

[hfleming]

I recently bought an expensive toy - a Siglent SSA2021X spectrum analyzer. I don't want to harm this not only because of the high purchase price. Hence my question, for simple tests and measurements on a Breadboard and with a signal generator in the 5 to 12V DC range, is a 20 dB attenuator sufficient as protection?

SSA2021X RF input
50V DC max - I have as additional protection a DC blocker
+30dBm max - which is one Watt (if I remember right)

With -20 dB from my external Siglent attenuator (20dB@4GHz) the SSA2021X should not be damaged till +50dBm ? Or is this false?

With my Oszilloskope the matter is much more relaxed, with 1 MΩ Input (instead 50Ω on the SSA), and the 1:10 probe you are relatively safe here with voltages not exceeding 24 V. I have no practical experience with specific RF performance. I don't want to analyze transmitters either, but rather interference signals in circuits, RF noise in my home office (switching power supplies, lamps).

Siglent has an app note showing something similar we used in the lab to protect our analyzers. It is just a pic fuse and an HV-blocking capacitor. In ours, we also added a PIN-diode limiter. A blown pico-fuse was a lot cheaper to replace than blowing up our very expensive R&S or HP spectrum analyzers. One common thing that inexperienced users did was to ignore large signals that is off-screen (like an oscillation, or the fundamental) whilst they zoom in on a very small signal.
The app note is here, but I am sure R&S, Keysight and Textronics will also have some similar notes.
https://siglentna.com/application-note/diy-spectrum-analyzer-input-protection

[Wallace Gasiewicz]

I'm also interested to this topic being the owner of a Siglent SSA3021X-TG and I have a simple and clear question :

what is the input power limit that guarantees that the instrument will not be damaged with ANY possible instrument setting ?

In my opinion this number should be available on the instrument datasheet.

I'm in the process to select a set of  attenuators in order to analyze the power output of some HAM radios, of course trying to keep the balance between instrument safety and S/N ratio, but I'm now understanding that is not an easy task 

For Ham Radios and also adjusting the stand alone power meters I use a JFW 100 Watt 3 GHz 40 dB Attenuator.   
I also use an HP Power Sensor and use a SA for Harmonics.    I think these things were bought for the cell industry and have good specifications...At 100 Watt testing it does get warm after repeated testing over several minutes. 
When I test power meters, you might be surprised at the results.....

JFW 50FH 040 100 3N

I also have a much bigger oil filled Load that has a "take off" or Sampler connection that is not linear but can be easily calibrated out...( no bumps but a sagging signal at low end)   I THINK it works out to decreasing the signal by 60 dB....I would have to check.   It is a Military BIG Thing.  Great for Linear Amps.

[tautech]

FWIW
In all SSA/SVA models, Attenuator settings in the Amplitude menu are best left set to Auto and any additional external attenuation compensated for in the Ref Offset settings so to negate any need for level maths in the head on the fly and to have Marker level measurements autocorrect for external attenuation values.

A couple of no signal screenshots showing these settings, one with external 10dB attenuator added and Ref Offset changed. Note the marker level remains similar only reading the noise in the no signal sweep.

As levels get closer to 0dB and above, these analyzers will auto-change internal attenuation to protect themselves.
Use a Manual attenuator setting at your own risk.

[vsilves]

Old thread but looking around the forum did not find a better match. 

I have been using a couple of old pin diode limiters from eBay (HP / Agilent 5086-7261, rated DC-2.5GHz) to protect my Siglent SSA3021X Plus on occasions, in addition to internal and sometimes external attenuators.  I don't have a data sheet for the HP 5086-7261 (the closest data sheet I found is for the Agilent 11867A which goes to 1.8 GHz, first picture is a graph from Agilent 11867A data sheet).

Today, I decided to verify that the two HP 5086-7261 limiters that I own actually work. Should have verified before using!

I don't have a lot of gear that outputs both high power and at high frequency, so I used my Siglent SDG2042X which only goes to 120MHz. Tested at 10MHz and at 120MHz, up to max output power available for simple sine wave.  The labels on the limiters are one black and one blue so I build graphs for both separately and, long story short, they seem to do what they are supposed to.  On the blue one I added some additional points using a LNA and an additional 10dB attenuator to increase the SDG2042X output power a bit (a bit messy up there but gets the point across).

Likes are: (1) the close to 0 insertion loss, (2) no clamping below 0 dBm (these limiters are supposed to start conducting at -10dBm and start clamping above 0dBm from what I read, results kind of confirm that), and (3) the rating for 10W continuous and 100W transients which I think are supposed to be clamped down to below 20dBm in the worse case, something that the internal auto input attenuator of the SA is supposed to be able to handle (as it goes up to -50dBm so long as the reference level is set high enough).

The good news is that I did not blow up the SA, in spite of using a roughly 30 dB LNA, or the 10dB external attenuator (rated for 2W, but got quite hot while handling the roughly 1W for several minutes while I jotted down numbers).  Had to double-check 10dB attenuator as I suspected damage.

In my limited experience, using reputable pin diode limiters in combination with attenuators is the way to go for input protection in certain situations (not only attenuators).

[fourfathom]

Can you test for harmonic generation vs input level?  This is critical for many measurements.

[vsilves]

Can you test for harmonic generation vs input level?  This is critical for many measurements.

Harmonics are all there, but they go away below 0 dBm.  See graphs at 20, 10, 0, -1, -2, and -3 dBm.