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looking for spectrum analyzer / network analyzer with 1MOhm Input Choice

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Performa01:

--- Quote from: rhb on December 12, 2018, 06:01:17 pm ---The FFT "spurs" may be self noise of the DSO.  I've been investigating that the last few days.  Set the instrument to the minimum V/div setting, stick a 50 ohm terminator on the input  and take a look at the FFT.  Arguably a 1 Meg termination would be better, but I didn't have one.

--- End quote ---
Can you quantify the spurs you're seeing - or even show a screenshot?

Is there a significant difference between terminated and open input?

Andree Henkel:
Hy, I have some questions regarding the differences between HP3588A and HP35889A

I understand, that the xxxx9 is a network analyzer.
It does complete S-Parameter (it delivers all 4 complex numbers s11,s12,s21,s22) measurement, provided you combine it with the external S-param testset.
As I understood the base unit includes tracking generator, choice of 1M input and capability to measure complex s11 including phase information.
It then can display phase plots, group delay plots and smith chart for s11

The capabilties of xxxx8 are somewhat unclear to me. Different sources of info are partially contradictory; so basically I have 3 questions
Q1: does it have 1M input choice also?
Q2: does it have a tracking generator?
If Q2 is yes
Q3: can I measure phase of s11?; I sure can measure amplitude of s11 (even without tracking generator, but then I would need additional white noise source)

PartialDischarge:
Hardware-wise both are the same, except for the CPU board. Both have 1M input, and tracking generator, but the 3588 will not make log-sweeps and will not give you phase info, so other options like polar, smith chart and Re-Im are also missing. The menus are not exactly the same also, they have tweaked some things that appear on the x9 and not on the x8

Just for the log-sweeps the 3589 makes a difference, some images of it, filters and a 10000x resistive divider. It can be connected via GPIB using this utility (http://www.ke5fx.com/gpib/readme.htm) although I've been too lazy and still rely on pics


Andree Henkel:
Thankyou, so well yes in case we go for the vintage unit, I´ll go for the xxxx9. While the xxxx8 would be all needed for noise measurement and spur detection, the xxxx9 could be really helpful if we are investigating things like stability issues caused by insufficient phase margin in current control / power control loops. The used xxxx9 aren´t that more expensive than the xxxx8.

I´ll present both variants the vintage and the new FSV4 to my teammates and manager of development, then we will decide which way to go in budget planning.

For short term I´ll order the 1M buffer amp linked to work with the R&S FPC1000 low cost Spectrum analyzer we have already.

Andree Henkel:

--- Quote from: rhb on December 12, 2018, 06:01:17 pm ---The FFT "spurs" may be self noise of the DSO.  I've been investigating that the last few days.  Set the instrument to the minimum V/div setting, stick a 50 ohm terminator on the input  and take a look at the FFT. 
--- End quote ---

I doubt, that the spurs shown in one of the 2 Screenshots of my RTA are caused by internal noise sources, if so they should likely show up in both screenshots. Even worse the actual existing spurs are missing in one screenshot while the other displays them correctly. The only change in setting I actively do between the two pictures is changing the timebase.
So yes, in my opinion more likely the origin of the problem in case of the RTA is some bug in the FFT implementation. Changing timebase sure has effect on the aquisition process and the intertwined parameters off FFT processing. But correct FFT implementation needs to take care for that.
All other scopes around here are more noisy than the RTA.

I´ll try to update Firmware and look if that helps. Result of that I´ll report here. If it doesn´t help I´ll report the issue to R&S.

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