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SSA2021X - 20 dB attenuator sufficient?
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fnaumann:
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).
Kim Christensen:

--- Quote from: fnaumann on January 13, 2024, 02:27:29 am ---With -20 dB from my external Siglent attenuator (20dB@4GHz) the SSA2021X should not be damaged till +50dBm ? Or is this false?
--- End quote ---

Partially true. +50dbm is 100 watts, so your 20db attenuator would also have to be rated for 100W. If it's not, and it burns out when you put 100W into it, you might get more than +30dbm into your SA.

12VDC into 50 ohms is 2.9 watts, so that would damage the typical 1W attenuator, but your SA is rated for 50Vdc with the DC blocker so it should be OK in that scenario.
fnaumann:
The situation is worse than expected.

"The maximum input values of +30 dB only apply if all attenuators are present in the device are raised to maximum."

https://www.microcontroller.net/topic/521714

I read on the internet that the direction of attenuators also matters and that you shouldn't buy cheap Chinese parts. Regardless of the fact that the expensive equipment sold in Europe is also produced in China, my "Siglent ATT-20 20 dB Attenuator" (https://www.siglent.eu/product/1141970/siglent-att-20-20-db-attenuator) has no label which direction is the correct one. Similar issue with my BLK-222+ DC blocker.

The Tracking generator of the Siglent SSA2021X

Output level -20 dBm~0 dBm
Output level resolution 1 dB
Output flatness +/-3 dB

should not harm when connect to the input ?
Kim Christensen:
There should be no problem connecting the output of the SSA2021X's tracking gen to the SSA2021X's input. Usually this is how you calibrate it anyway.

I can see direction being an issue with some high power attenuators, but not with a 1W one or less.
For example, if the input is on the left you can see there'd be more power dissipated in R1 than in R3. So on some larger attenuators I can see them making R1 higher wattage than R3. But on a low power one, they are usually the same wattage and thus 100% bi-directional:

fnaumann:

--- Quote from: Kim Christensen on January 13, 2024, 09:18:40 pm ---There should be no problem connecting the output of the SSA2021X's tracking gen to the SSA2021X's input. Usually this is how you calibrate it anyway.
--- End quote ---

That was my first thought, but the many warnings I found on the Internet about spectrum analyzers confused me.


--- Quote from: Kim Christensen on January 13, 2024, 09:18:40 pm ---I can see direction being an issue with some high power attenuators, but not with a 1W one or less.
--- End quote ---

Here (see attached picture) are two of my 20 dB, 50Ω  which covers a frequency range till 4GHz. One slim (with BNC connectors) for 1W (30 dBm ?) and a fat one for 10W. If I understand you right, I should not use the 10W attenuator as input protection for my SSA2021X?

based on https://www.siglenteu.com/wp-content/uploads/dlm_uploads/2017/10/SSA3000X_DataSheet_DS0703X-E04A.pdf

Maximum average RF power 30 dBm, 3 minutes, fc≥10 MHz, attenuation >20 dBm, preamp off
Maximum damage level 33 dBm, fc≥10 MHz, attenuation >20 dBm, preamp off

The output level of the Tracking Generator looks save

Output level -20 dBm~0 dBm


I know my questions are at Newbi level. Could we compare it with the DC area. Two 1Ω resistors, one with 5W and the other with 50W. If the voltage and therefore the current flow becomes too high, the resistor burns out, depending on its respective power value. When this burns down, the bond is dead and no damage can be done to the other side of the resistor. If the same applies to attenuator, what's the problem? Or does the attenuator then switch fully on without any attenuation?
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