Hi:
I am fairly new at using this instrument (Newbie Alert), so this may simply be pilot error, or lack of experience.
We were looking at three different benchtop signal generators today at 10Mhz (HP, Marconi, Siglent 2042x),
to look at the waveform, noise, and spectral purity. In all three cases, the 10Mhz signal from each generator showed
what looks like a pair of angel wings surrounding the main carrier. On either side of the main carrier vertical spike,
there was a dip, and then a climb to a higher noise level, and then a very gradual trailing off. But on the Rigol DSA-815
analyzer, all three signal generators had a more traditional/expected gradual rolloff/curve away from the main carrier.
A screenshot is attached. I tried various values for span, RBW and VBW, including 1/3 ratios for RBW and VBW.
Am I using it wrong, or is this some artifact of the Siglent SSA-3021x? Or worse yet, is this an issue with my specific
unit and main clock jitter or phase noise?
Neal
It is nominal to this SA. It is just this SA Phase Noise distribution shape + random noise + signal under test phase noise where is SA own PN is most dominant and small amount of other things.
Near carrier Phase Noise is better than more far from carrier until it again start drop. If can not drop more far carrier PN but if can drop near carrier PN I think is is good. Look example some nonamed around same price class competitors where PN specifications are close same in data sheet but when you go to 100Hz from carrier PN may masks all under noise and with this you see lot of more deep... I can see this is advantage, not disadvantage. Of course it is best if 20kHz and more from carrier can drop but there is price...
So it give small advantage for look bit more deep things very close carrier due to fact that RBW shape factor is around 1:5 and so with 1Hz RBW you can go really close carrier with quite far below carrier level for example find signal generators impurity very close carrier and get example some image about residual FM etc
Also it is well inside specs in this noise figure / and partially phase noise meaning what can see in your image.
Be careful with ExtRef related to Phase Noise. If you do not really need ExtRef for reason to keep perfect frequency and perhaps sync with other equipments, just Do Not use it except if it is real important for freq. For PhaseNoise, Ext ref, even if it is state of art class, looks like can not make it any better due to my tiny experience with this SA but it can do it more bad if it is bad. (In this image I can not see any notable rise or drop in PN from nominal.)
If you are not familiar with SA you can read very good material like example Keysight good application note AN-150 pdf
It is nearly like material what is good to read for every single SA owner, even bit more experienced or first time user. No need understand all. Of course there they talk also about MUCH more expensive SA things but most basic fundamentals are same.
Of course available is many kind of materials but this one is also theoretically quite high quality and reliable.
https://www.ab4oj.com/test/docs/5952-0292.pdfYour SA is of course not analog, so you need read what is told about full digital IF SA but also read these basic fundamentals even when your SA is bit different. There is lot of same what is explained this originally HP / Agilent application note
You may be amazed how many things are there explained just as it is also in your SA.