Question about Agilent N9340B spectrum analyzer Mixer Saturate warning - Page 1
Forum section: electronics / testgear

author: analogRF
author_rank: Super Contributor
timestamp: December 27, 2020, 03:48:32 am
content: I have a fully working N9340B which measures quite accurately but there is an odd issue which is very annoyingUsually in spectrum analyzers, input signal can go few dBm above the REFLVL before the instrument warns the user about first mixer being overloadedhowever in this SA I cannot even go 1dBm above REFLVL and it if i do it instantly writes a warning message at the bottom of screen saying:"149  Mixer Saturate"Despite the warning, measurements are spot on and there are NO spurious tones being generated which indicates to me that the first mixer is not actually overloaded.If somebody out there has one of these at hand, can you please check and let me know if this behavior is normal?EDIT: Perhaps i should also mention that this happens with the default (Auto) settings of attenuator and REFLVL. I mean if I increase the ATTENby let's say 5dB without changing the REFLVL then I can go 5dBm above REFLVL but not more at all. even 0.5dBm more gives the warning

author: SilverSolder
author_rank: Super Contributor
timestamp: December 27, 2020, 03:26:55 pm
content: Isn't the warning technically correct, if the mixer really is being overdriven (even if you know what you're doing, as you obviously do)?

author: analogRF
author_rank: Super Contributor
timestamp: December 27, 2020, 03:48:01 pm
content: yeah, but I am expecting it to happen when I go like 10dBm above REFLVL (some analyzers even allow you to go further) before the warning appearsbut this thing warns right at 0dBm+anything. Even 0.1dBm above gives warning, so the error list sometimes gets filled up with all these nonsensical warnings.I am hoping someone with a N9340B can do a simple test and see how it behaves.

author: analogRF
author_rank: Super Contributor
timestamp: December 28, 2020, 04:32:43 am
content: I dug deeper into this and made a series of tests with many combinations of input signal power and ATTEN setting.It is now clear to me that the analyzer is set to complain (warning) as soon as the input power to the first converter passes ever so slightly -20dBmThe input to the mixer is basically equal to (INPUTdBm-ATTENdB) with preamp off. So as long as this quantity is <-20dBmNo warning appears and as soon as this quantity is even a tiny bit above -20dBm it complains. So basically it is completely independentof the REFLVL setting which makes sense now. The reason that I first notice that by changing the REFLVL was that when you change REFLVL the ATTEN setting changes automatically (these two are coupled by default).But why is it so damn fussy about this? I mean there should be some tolerance. Actually if I set my sig gen power such that the mixer input is exactly -20dBm most of the time I still get the warning because perhaps the actual value is like 0.1dBm or something higher!Still I appreciate if somebody could confirm this behavior in their N9340B.

author: analogRF
author_rank: Super Contributor
timestamp: December 29, 2020, 12:40:06 pm
content: Does anybody have an N9340B here?I just would like to know whether this behavior that I explained above is normal and how sensitive it is.Even a 10MHz or 50MHz signal will do the job. Set the amplitude to 20dB lower than your ATTEN setting and see if it gives a Mixer Saturate warningand play with the input signal for like +/-2dBm to see how sensitive it isThanks