Products > Test Equipment
SSA2021X - 20 dB attenuator sufficient?
fnaumann:
--- Quote from: blackdog on February 05, 2024, 10:36:29 am ---I don't know your environment, if you have a hobby room surrounded by your family who each have a cell phone then the power you get in at an unfavorable time can be quite high.
Also if you have radio amateurs nearby the power if you mount an antenna on your SA can be a problem.
--- End quote ---
A few iPhones are flying around near me. And the neighbors next to and below me will also use smartphones. No radio amateurs as far I know.
--- Quote from: blackdog on February 05, 2024, 10:36:29 am ---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 ---
This annoys me as a spectrum analyzer beginner - the thing is apparently so sensitive that you have to handle it with kid gloves. An oscilloscope is a much more robust part, especially if you use a differential probe (and do not need to cover a common ground). I'm honestly disappointed with the SSA use cases shown in YouTube videos. I can do a lot of antenna-related things much more relaxed with my NanoVNA-F V2, and other things with my SDR boxes. Above all, the FM and AM demodulation function on the SSA is a joke (completely unnecessary in my opinion). And then I now have a TinySA Ultra - which in one of the videos even offers a smaller noise floor. I know I can not compare a TinySA Ultra with a Siglent SSA2021X , but ....
blackdog:
Hi fnaumann,
The point is to be careful, my spectrum analyzer has a limit of 100mW at its input.
If you put a pickup antenna next to a mobile phone, you can get over this limit.
The phone transmits not only when you make a call, it does this just when it feels like it. :-)
But don't get paranoid, it's all about being careful with your measuring equipment.
The 10 0f 20dB attenuator at the input you start with during a measurement session normally makes the SA indestructible.
( if you ar not doin measurement on tranmitters!)
The field of an antenna connected to a transmitter decreases quadratically with distance.
So if the distance to a phone is 4-meters, and you double this to 8 meters, then only 1/4 is left.
The manufacturers of this kind of measuring equipment have to perform tricks to get a good noise number, good distortion value and then also have a "decent protected" input, it is not easy.
Greetings,
Bram
EggertEnjoyer123:
--- Quote from: fnaumann on February 05, 2024, 08:47:47 pm ---
--- Quote from: blackdog on February 05, 2024, 10:36:29 am ---I don't know your environment, if you have a hobby room surrounded by your family who each have a cell phone then the power you get in at an unfavorable time can be quite high.
Also if you have radio amateurs nearby the power if you mount an antenna on your SA can be a problem.
--- End quote ---
A few iPhones are flying around near me. And the neighbors next to and below me will also use smartphones. No radio amateurs as far I know.
--- Quote from: blackdog on February 05, 2024, 10:36:29 am ---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 ---
This annoys me as a spectrum analyzer beginner - the thing is apparently so sensitive that you have to handle it with kid gloves. An oscilloscope is a much more robust part, especially if you use a differential probe (and do not need to cover a common ground). I'm honestly disappointed with the SSA use cases shown in YouTube videos. I can do a lot of antenna-related things much more relaxed with my NanoVNA-F V2, and other things with my SDR boxes. Above all, the FM and AM demodulation function on the SSA is a joke (completely unnecessary in my opinion). And then I now have a TinySA Ultra - which in one of the videos even offers a smaller noise floor. I know I can not compare a TinySA Ultra with a Siglent SSA2021X , but ....
--- End quote ---
You can get a lower noise floor by turning the resolution bandwidth down. (The tradeoff is that it'll take longer to sweep).
For low frequency stuff (like maybe under 50 MHz), a scope is usually better, but once you get to high frequencies scopes become prohibitively expensive. Also, high frequency scopes have 50 ohm inputs too and most of them can take even less power than your spectrum analyzer.
If you want to analyze noise around your house you should look at making a near field probe (There's a EEVBlog video on making your own out of coax). Connecting that directly to the spectrum analyzer should be perfectly fine (as long as you don't put it in the microwave or something).
fnaumann:
--- Quote from: EggertEnjoyer123 on February 05, 2024, 09:20:31 pm ---You can get a lower noise floor by turning the resolution bandwidth down. (The tradeoff is that it'll take longer to sweep).
--- End quote ---
I know this. Watch this starting at minute 16.
fnaumann:
I did my own testing with my SSA2021X and TinySA Ultra using a test signal from my SDG 1032X.
The signals were clearly visible on the TinySA Ultra out of the box. With the SSA2021X, the signal was also visible after various adjustments, but with significantly more noise. The signal/noise ratio seems scary to me as a layman. I tried to set the SSA2021X using various options so that I could see the test signal better on the display. As a test signal I used a simple 10 MHz sine wave signal with 1 to 5 dBm output level (SDG 50 ohm output mode).
To protect the SSA, I installed a 30 dB attenuator (10 W) plus a DC blocker. I reduced the internal attenuation to 0 dB (after the signal-to-noise ratio didn't improve much). Which doesn't make it much better. I also tried different bandwidth settings.
Then when I activated the internal preamp, the SSA beeped and warned of an overload situation. What crap. :-- The SSA is specified as a maximum of 30 dBm and 50 V DC. Of course, these values are only given for special settings. But - I had used a maximum of a 5dBm signal with 30dB of external attenuation, which corresponds to a -25dBm input signal? How can a -25dBm signal produce an overload warning on the SSA? I only activated the PreAmp option under “Amplitude” without setting a manual value. Shouldn't the software prevent overload?
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