First time spectrum analyzer Use (Siglent SSA 3021X) - Page 1
Forum section: electronics / rf-microwave

author: JaPaBo
author_rank: Newbie
timestamp: September 03, 2020, 05:58:51 pm
content: Hi All,I'm attempting to use a spectrum analyzer for the first time and having a few difficulties. I'm not getting a meaningful response using an antenna or near field probes when the system under test is on (I do see background noise from the anteanna). I'm trying to perform precompliance FCC testing. Unit has a preamp which is turned off and an attenuator which is set to automatically attenuate the input signal.1. With no probe or input connected, I see the meter response spike at lowest frequencies (attached images). This is also observed with a biconical antenna connected. I've seen similar in other tutorials/videos on Youtube so maybe it's not a concern. Can anyone explain this? Does it suggest the front end is damaged? Is this spike affecting the autoattenuation?2. Is there a way to measure the total input power to ensure I stay below the 30 dBm limit to prevent damaging the unit? I'm concerned about using the preamplifier or disabling the attenuator otherwise. Maybe I'm being too conservative as a result of this confusion and not seeing expected signals...Thanks for any advice!

author: Gribo
author_rank: Frequent Contributor
timestamp: September 03, 2020, 06:40:03 pm
content: What are you transmitting? What band? Bandwidth? Data rate? Is it CW (Constant wave) or sporadic transmissions?

author: JaPaBo
author_rank: Newbie
timestamp: September 03, 2020, 06:53:04 pm
content: I'm trying to take measurements of a switching power supply radiated emissions from 30 MHz to 1 Ghz in an unshielded room. It should be continuous (though I can turn the supply on/off and background noise may change over time).

author: JaPaBo
author_rank: Newbie
timestamp: September 03, 2020, 07:49:45 pm
content: I think similar output response at low frequency is visible in the first figure of the following two App notes from Siglent (with linear x axes):https://siglentna.com/operating-tip/noise-floor-analyzer-raise-enable-tracking-generator/https://siglentna.com/application-note/spectrum-analyzer-basics-detectors/I'm not really sure what to make of this given the 9kHz bottom end frequency for the unit.

author: RadioNerd
author_rank: Regular Contributor
timestamp: September 04, 2020, 07:02:10 am
content: The tesolution bandwidth is set to 1 MHz... What you are seing is most probably the analyzer's DC spike extending over the first MHz of the sweep. Due to the log frequency scale the low frequency part is looking much wider than it actually is...Switching to linear frequency scale will make things look more intuitive

author: tautech
author_rank: Super Contributor
timestamp: September 04, 2020, 10:06:47 am
content: Quote from: JaPaBo on September 03, 2020, 05:58:51 pmFor near field probes you will need the Preamp ON.Leave the attenuator set to Auto and work with 1 GHz max frequency.....sometimes just 500 MHz is enough especially when you need to zero in on the emissions.The unit will give visible and audible warnings should input signals get close to max.Question, SSA3021X or the later Plus model ?If the Plus, check out the latest user manual section on EMI as there's a new EMI mode that takes a big of getting your head around however the manual give some reasonable guidance on how to use it.

author: JaPaBo
author_rank: Newbie
timestamp: September 04, 2020, 03:25:21 pm
content: It is a "Plus" model with the EMI option.I was able to correct/control the lower frequency spike by changing resolution bandwidth - pretty sure RadioNerd's explanation is correct.Thanks to all for the inputs!

author: tautech
author_rank: Super Contributor
timestamp: September 04, 2020, 03:33:55 pm
content: Quote from: JaPaBo on September 04, 2020, 03:25:21 pmOK. with the latest firmware ****.8 there is a new EMI mode. Press the Mode button to select it.Released at the same time is a user manual update with a new section on this new mode.New EMI mode GUI posted in another thread:

author: JaPaBo
author_rank: Newbie
timestamp: September 04, 2020, 06:13:23 pm
content: Thanks for mentioning the EMI mode - it's not present with our current firmware (2.2.1.2.5). I will update!One more question - I'm looking to take measurements using a Tekbox TBMA1 biconical antenna. Tekbox provides antenna factors (dB/m units) with the antenna. It appears that these numbers should be directly entered into the spectrum analyzer correction tables with no modification or sign changes. Can anyone confirm that this would be the correct approach? I've attached an image of the vendor's measurements and of the anayzer's interface for correction data for reference. Thank you!

author: tautech
author_rank: Super Contributor
timestamp: September 04, 2020, 08:31:50 pm
content: Quote from: JaPaBo on September 04, 2020, 06:13:23 pmDon't know the new EMI mode very well yet however I think you will add the corrections intoMeter Config.It shouldn't be hard to cross check, take 2 measurements, one with corrections added and one without.One should be your correction value higher.Probably with the amount of gain your antenna provides the Preamp won't be necessary.Edit.After a look as to how you would apply corrections for EMI antenna it seems only in the Amplitude menu in Corrections where you can set 4 of them.