Products > Test Equipment
Zero span spectrum analyzer .FFT, sweep, filters and RBW.
<< < (7/8) > >>
G0HZU:
On narrow spans, the dynamic range of the Siglent analyser will be phase noise limited. So I guess one could conjure up scenarios where a large adjacent signal can spoil zero span mode (with a 30Hz digital RBW) through reciprocal mixing (noise).

However, this is going to be a rare event.

Overall, the difference between the Siglent analyser and a high end lab analyser is that the lab analyser is designed to be able to measure very small signals that are close to 'very' large signals. The Siglent analyser can't compete here. It can easily have 20 to 30dB less dynamic range compared to the lab analyser in some tests.

My interpretation of the Siglent datasheet is that it can't offer a digital RBW less than 30Hz in swept mode. Therefore, this doesn't just impact zero span mode.
xugmu:
I deduce from your fantastic comments and images that it is not possible, not even with high-end analyzers, to get a stable "analog" RBW (sweep) in the 1Hz range. Therefore, everything that is done in that resolution range is done with digital technology (FFT) so it does not matter if, in that range, a manufacturer announces sweep or FFT.

The target to analyze are pilot OFDM carriers with a bandwidth of approximately 1kHz where there is quite a difference (especially in the waterfall) between 1Hz and 10Hz.

Getting a high SFDR or many preselector input filters is totally beyond my economic possibilities and, as you have said, buying a measurement device must depend on the needs.

Best  regards
hpw:
As I see, you will get any better results using a PN noise measurement system. Additional using an accurate down mixer as here posted. Not to forget the AM/AN spurs as looking PM/FM O;)

The link here to the product, will show only single band.

https://qsl.net/bg6khc/pn2060c_phase_noise_analyzer.htm

My measurements as you like to do, as simple using a 10MHz reference 1Hz@-120dBc and comparing the SSA30xx showed clearly the side PN/AM of the internal synthesizer.

just my 2 cents

hp
G0HZU:

--- Quote from: xugmu on August 07, 2024, 02:02:30 pm ---I deduce from your fantastic comments and images that it is not possible, not even with high-end analyzers, to get a stable "analog" RBW (sweep) in the 1Hz range. Therefore, everything that is done in that resolution range is done with digital technology (FFT) so it does not matter if, in that range, a manufacturer announces sweep or FFT.

The target to analyze are pilot OFDM carriers with a bandwidth of approximately 1kHz where there is quite a difference (especially in the waterfall) between 1Hz and 10Hz.

Getting a high SFDR or many preselector input filters is totally beyond my economic possibilities and, as you have said, buying a measurement device must depend on the needs.

Best  regards

--- End quote ---

I'm still a bit unsure what you are trying to say here.

If you go back over 30 years, almost all spectrum analysers had analogue RBW filters built using LC resonators or with crystals. These have poor shape factor and the sweep speed has to be really slow for an analogue 10Hz RBW filter. A 1Hz RBW filter would be extremely slow. I've used analysers with a 3Hz analogue RBW filter and the sweep time is painfully slow.

In the 1990s, analysers started including digital RBW filter technology for the narrowest RBW filters. These offered much improved shape factor and faster sweep times for a given RBW.

The digital RBW filter is generated in the digital domain rather than the analogue domain. It's possible to have a digital RBW down to about 1Hz BW on a decent lab analyser. A digital RBW filter is usually fixed at the IF frequency and it works in conjunction with a swept LO, just like the analogue RBW filters except the digital RBW filter is synthesised in the digital domain.

This process doesn't involve FFTs. Digital RBW technology is different to the FFT method.

Later analysers had more advanced ADC and DSP technology and this allowed fairly large FFTs to be run over a fairly wide bandwidth.
In this case, the RBW is defined by the sample rate and the FFT size and the window function. This is very different to the way a digital RBW filter is generated in the digital domain.

I have very little experience with OFDM stuff. You may be better off with a decent SDR or RTSA although I'm still not sure what you are trying to do.

A digital RBW filter with 1Hz RBW will have a very slow response time to any changes in signal level and this can cause some confusion. For example, if the signal was instantly gated off, then the analyser might take several seconds to actually show that the signal has completely gone. Similar things (even more confusing?) will happen if you try and use FFT mode.

So I'm not sure what you want to see if you select zero span with a 1Hz RBW. The system will be very sluggish to report any changes in signal level to the point where I'm not sure how much use it would be in your case of an OFDM signal.





G0HZU:
I think I can generate OFDM signals here using an old Agilent signal generator and some Agilent SW. This generates 802.11x test signals for wireless LAN. Is this similar to what you are looking at?

I've got various spectrum analysers here but rarely use them for looking at stuff like WLAN. I don't know much about WLAN. However, I could try and look for the same thing you want to see?


Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod