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 Post subject: SSA3000X: know the device - for better measurements
PostPosted: Tue, 14 Mar 17, 09:14 
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Joined: Sat, 30 Jun 12, 12:59
Posts: 369
Location: Finland
Before you can successfully use SSA3000X you may need more or less exercises and study. Depending what you are doing, what is your education, what is your experience with this kind of units.
Some times experience example with very different SA's may do things more difficult because you need perhaps also unlearn some things related to different equipment. Specially if you have experience with full analog SA and not full digital IF SA's.

It is also good to know some things about principles how these machines work.

There is lot of free study material available.
Years I have recommended this and - this is really good.
Note that there is handled analog, "semi" digital and also full digital like SSA3000X series (of course in this paper they talk about HP(Agilent/Keysight but Siglent do not differ so much.)

Please read this and keep it also available for later use. (pdf)
Agilent Technologies, Spectrum Analysis Basics, Application Note 150

Soon I will take one thing what sometimes some users may wonder.

I make one example.

There is two CW carrier, close each others. You want measure power sum of these.
Easy you say. Yes - or hmm... wait a moment. Is it?

Many times good solution is: Measure these carrier levels separately. With this SA it is quite easy because there is available mostly enough resolution. Most narrow RBW is 10Hz ! And also these IF filters shape factor is <1:4.8 @-3dB/-60dB. They are not analog hardware filters, they are all DSP made filters. Just example if you have two 8MHz carrier and example 1kHz distance from each others. Just take example 10kHz Span and RBW 100Hz. With RBW 10Hz you can measure separate peaks even if they are <50Hz distance.

Just measure peak levels and calculate. Example if there is two -10dBm peaks. -10dBm is 0.1mW. Two 0.1mW peaks is 0.2mW. 0.2mW = -7dBm (-6.9897dBm)

This is simple method but need calculations. Good thing is that you also see these peaks even if they have very different level. Think if you have -10dBm and -30dBm peaks there. 0.1mW and 0.001mW. It is -9.9568 dBm. You may see only 0.04dBm difference if SA show these added.

In all cases if there is two CW and you remove one what is lower or equal than other you can see max 3dBm change in total combined power and if difference is big, you hit very easy resolution and far before you loose resolution you are out of accuracy.

How to measure combined power.

Base principle is very very simple if signals are near each other so that they can be inside RBW filer top. But... this need more explanation for avoid traps and need understand some basic things.

Under work.
To be continue.....

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 Post subject: Re: SSA3000X: know the device - for better measurements
PostPosted: Tue, 14 Mar 17, 10:34 
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Joined: Sat, 30 Jun 12, 12:59
Posts: 369
Location: Finland
THIS IS NOT READY YET need edit and add more info etc!!!!!!!!!!!!


Here is two CW carrier. Both around -10dBm level. Other is 8000000Hz and other 8010000Hz
First three images show settings how they are in menu system..
Sweep mode Sweep.
RBW=VBW=1kHz
BW menu average type Power
Detector Average RMS
Span 100kHz
Center 8005000Hz

As can see SSA markers show around -10dBm for both peaks. (absolute accuracy is not this and I have not measured true perfect accurate power for these carriers. But sure is that error to real -10dBm is less than 0.5dBm.

Then change RBW so that both are inside center of filter. Span still same 100kHz
Result: OK around -7dBm - which was of course expected

Then change Span to 1MHz keep same RBW
Result: OK around -7dBm - which was of course expected

This kind of measurement need do like this and it need also care that sweep time is enough long even if SSA try select faster sweep time.

SA can not do thinking, it is just stupid simple machine - the user must perform brainwork. For help thinking there is lot of free literature available around.

This is one what can say - it is mandatory to read: http://cp.literature.agilent.com/litweb/pdf/5952-0292.pdf

Specially things what are there about full digital IF SA's.

The user must note that these fast hopping modern full digital IF SA's work very very different if compare to old analog sweep analog IF SA's. If the user is accustomed to using an analog spectrum analyzer. One of the most important task is to learn new things, but at the same time need to unlearn some things. Otherwise, may fall in to some trap. Who is then wrong, equipment or user?

One of most important thing is: Know your equipment!


Image
These first 3 images same but show different menu settings. Peaks both -10dBm
SSA is running and just sweeping without trace average. Snap shot on the fly.


Image
These first 3 images same but show different menu settings. Peaks both -10dBm
SSA is running and just sweeping without trace average. Snap shot on the fly.


Image
These first 3 images same but show different menu settings. Peaks both -10dBm
SSA is running and just sweeping without trace average. Snap shot on the fly.


Image
Signal is exactly same what in first 3 images. --> RBW 100kHz Level now -10dBm + -10dBm = -7dBm = OK
SSA is running and just sweeping without trace average. Snap shot on the fly.



Image
Signal is exactly same what in first 3 images. --> Span 1MHz Level now -10dBm + -10dBm = -7dBm = OK
SSA is running and just sweeping without trace average. Snap shot on the fly.


[size=3pt]For thinking: there is one "secred" word...and it is.............. phase
(signals phase difference)....oh well there is also other things but...[/size]

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