Siglent SSA-3021X Spectrum Analyzer Amplitude is off - Page 1
Forum section: electronics / testgear

author: kr5j
author_rank: Contributor
timestamp: February 14, 2018, 01:50:10 am
content: My Siglent SSA-3021X spectrum analyzer seems to be off by 4.5 dB. I measured the 50 MHz Cal Signal on an HP E7475A test set and it reads -4.97 dBm for a 0 dBm ref signal. The 50 ohm test cable measures a loss of -0.4 dB. Anyone else have this issue?

author: TheSteve
author_rank: Unknown
timestamp: February 14, 2018, 01:52:20 am
content: What RBW and span are you using? Maybe post a screen shot.

author: rf-loop
author_rank: Super Contributor
timestamp: February 14, 2018, 07:49:39 am
content: Quote from: kr5j on February 14, 2018, 01:50:10 amI do not know E7475A GSM Drive Test System calibration signal and its reliability or accuracy.If it is around same as 50MHz 0dBm Cal signal availabe example in HP rf power meters least they are typically accurate and reliable with level. (freq is not at all accurace and drifting also lot but total out power level (including effective harmonics!) in these is - good. (here if want real high accuracy, dpending cal signal features, need take also care about harmonics power and not only base freguency aka 1st harmonic)Do you have any other pure sinewave signal source with reliable and accurate carrier level say example between 5 - 200MHz and so that also impedance is reliable and accurate.Some tests (but my suspect is even now 1st GaAs SPDT switch just after input.)Set source for 0dBm (make sure its 1. harmonic (carrier) absolute accuracy is better than +/- 0.2dBm.Set SSA to full factory defaults. (50ohm impedance, no correction tables in use and detector PosPeak etc)Set SA center freq for this carrier freq. Set span for example 1MHz and RBW 30kHz.(best to use Span/RBW between 3 and max 100 example Span 1MHz/RBW100kHz=10)Now SA Atten is 20dB and reference level 0dBm.Push marker "peak" for measure peak level with marker. Write down this measured level.Keep reference level 0 adjust Attenuator from 20 to 51dB and watch signal levels (if test signal drift, position marker pushing again "peak"). Watch level do not change more than 0.5dB. If change write change down.Set test signal for -20dBm.Turn SA attenuator fo 0dB. Reference level is now -20dBmPush marker "peak" for measure level.Turn SA attenuator now from 0 to 51dB and watch levels and note if there is more than 0.5 (0.8 ) dB changes.If you have good reliable source up to 2.1GHz and very good known and short cable (do not even try with some total junk RG58 "audio" coaxial or "noname-no type" 50ohm looks like toy cable) do test with some upper frequency points also. If you have other good reliable meter (power/level meter or SA) what can use for cross check then this cable is not so critical because you can compare results)Btw, typically SA 10MHz freq reference output is around +3dBm.If not any other source, fast unreliable test canb do with this. Coaxial from 10MHz out to SA RF input.Span 1MHz, freq 10MHz, RBW 30kHz (also more narrow span and RBW can use of course. There is not physical RBW filters so they are around same just math. But there is other reasións why level measurements is better to do do so that span/RBW is not extremely high, example between 3 and 100.If you are sure your SA show some dB (something like ~2-5) too low levels roughly independent of frequency and attenuator level there is failure and it need Siglent repair. If this is case, contact your seller for arrange this. THis forum do not repair it. First place to contact is your seller distributor. This is sellers job. Sellers job is not just only collect money and resend retail box/carton. After sales customer care is also sellers job. Period.If you can enough reliable note this type of failure, it mostly tell that it is damaged by external EOS/ESD signal but of course itmay also be random component self failure.It need take really seriously that SA input IS really very sensitive and electrically very fragile.I know lot of peoples who underrate EOS and specially ESD. Even professionals. Just because they are under educated.But I know also opposite... overreact and mystify these things. And this is also education question.Never touch without enough ESD protection to any part of circuit what is directly going to SA input.Never ever connect any cable as "antenna" to input without real protection for EOS/ESD. 50V is really low. It do not mean only continuous 50V DC, even very extremely short peak over 50V is enough. (50 ohm impedance do not mean at all that it is not sensitive for ESD. Handle SA input like what ever ESD sensitive component. Because it is.One reason it is sensitive is that SA is build for very low levels over whole freq range. And input is always wide range sensitive even if you look 10kHz with 2kHz Span this input see whole RF band and is sensitive up to far over 3GHz.And if user use some span, example 100MHz center and 20MHz span. It give warning about too high level. But it do not at all warn if there is even highly over damage level signal outside of this freq range inside span.There is really many traps in real life what may lead to EOS/ESD situation and damage. It happens accidentally very easily including also experienced peoples.When input is failed it need repair.Also sidenote: some may thing that temporary solution before repair is just setup correction table for correct this level error (there is level correction table what user can make and use) example if there is some continuing level error. But, it is extremely poor solution because you can not trust anything, specially with bit higher frequencies. Why.Because after GaAs switch failure ( I suspect this switch in this case) there may be also very bad "what ever" input VSWR what may lead totally wrong measurements also depending signal source device features, traits. Some frequency may show too low level but then some freq may show even too high levels spending incoming and reflected wave phase.1. Do reliable measurements with some kind of cross checks. If result is fail without doupt, then2. Contact seller and tell this fail and ask repair.3. Follow instructions you get for possible more measurements and/or instructions for deliver to repair service.This is how it must go.If steps 2. or 3. fails, then contact directly Siglent for get help and instructions how to deliver it for repair service.Note: Siglent Head Office in China have vacation to 22th, Feb.This topic raises the importance of protecting spectrum analyzer input from EOS / ESD events. Even if it is not reason in this individual case.All we know old SA and they are very fragile if there is not DC block, internal or external. There is so many destroyed 1. mixers.These old SAs have typically mechanical step attenuator first and possoble some other not so extremely sensitive things but then mixer (because without DC block DC can go directly (Specially if Atten level is 0dB) from input to Mixer and destroy it (sensitive diodes).Here is not this in example Siglent SSA becausew there is fixed internal DC block what can not turn off. But, there is lot of things before mixer what also can damage very easy.Most vulnerable is very sensitive 3GHz GaAs SPDT switch what first take all in after DC block. One quite small ESD and it is gone. Switch that previously worked but not now anymore = dead.