Trying to understand HP8563E specification - Page 1
Forum section: electronics / testgear

author: tkamiya
author_rank: Super Contributor
timestamp: April 16, 2021, 05:00:40 am
content: I am trying to understand the specs of HP8563E, spectrum analyzer. According to marketing literature, it has a "fast digital resolution bandwidths" of 1, 3, 10, 30, and 100Hz. On other place, in spec sheet, it says minimum resolution is 10Hz, but VIDEO resolution is 1Hz. aaaand in some other place, it simply says 1Hz bandwidth.The way I understand RBW and Video bandwidth is that latter basically acts as a filter to smooth out the trace. Then what good is it to have 1Hz video bandwidth while real bandwidth is 10Hz? How digital resolution bandwidth different from regular bandwidth?It all sounds market mumbo-jumbo to me. If I wanted to see, say signals 2Hz apart, can I?https://www.keysight.com/us/en/product/8563E/portable-spectrum-analyzer-9-khz-to-265-ghz.htmlBTW, I currently have 8568B, 8591EM, and 8593E. I was wanting 1Hz resolution, if and only if it works to distinguish signals 1Hz apart. To me, that's "resolution".

author: kirill_ka
author_rank: Frequent Contributor
timestamp: April 16, 2021, 07:38:49 am
content: The 856XE series do have 1 Hz RBW indeed.Quote from: tkamiya on April 16, 2021, 05:00:40 amThat's an interesting experiment. I'll try this on my 8561E and report back.

author: kirill_ka
author_rank: Frequent Contributor
timestamp: April 16, 2021, 10:48:53 am
content: Well, I can't reliably see 1Hz separation. Every other sweep two signals appear as one.However the signals separated by 2Hz are always visible.

author: tkamiya
author_rank: Super Contributor
timestamp: April 16, 2021, 08:08:13 pm
content: That's nice. Thank you very much.Do you know what HP means by digital bandwidth? Is there analog and digital set up separately? The whole thing is not well explained in any of the manuals.

author: xmo
author_rank: Regular Contributor
timestamp: April 16, 2021, 10:40:31 pm
content: "We use the term “digital IF” to describe the digital processing that replaces the analog IF processing found in traditional spectrum analyzers.While the 1 kHz and wider RBWs are implemented with traditional analog LC and crystal filters, the narrowest bandwidths are realized using digital techniques.Once in digital form, the signal is put through a fast Fourier transform algorithm. To transform the appropriate signal, the analyzer must be fixed-tuned (not sweeping). That is, the transform must be done on a time-domain signal. Thus the analyzers step in increments, instead of sweeping continuously, when we select one of the digital resolution bandwidths."

author: tkamiya
author_rank: Super Contributor
timestamp: April 22, 2021, 06:46:48 pm
content: Appreciate that detailed information. Where did you find it? I'd like to read up on it if there are more.From user's prospective, are there any limitations using this technique?

author: kirill_ka
author_rank: Frequent Contributor
timestamp: April 24, 2021, 08:32:53 pm
content: Quote from: tkamiya on April 22, 2021, 06:46:48 pmhttps://www.hpmemoryproject.org/an/pdf/an_150-1989.pdf

author: xmo
author_rank: Regular Contributor
timestamp: April 25, 2021, 03:50:37 am
content: The digital RBW's in the ESA are 300 Hz and down whereas they are 100 Hz and down in the 8560E.The service manual says:Band 0 uses triple conversion to produce the 10.7 MHz IF and a fourth conversion used only in the digital resolution bandwidths (=<100 Hz).A8 dual band mixer up-converts the RF input to a first IF of 3.9107 GHz.A13 second converter down-converts the 3.9107 GHz IF to an IF of 310.7 MHz.A third conversion on the A15 RF assembly down-converts the second IF to the 10.7 MHz third IF.A fourth conversion on the A4 log amplifier assembly down-converts the third IF to the 4.8 kHz fourth IF used only in the digital resolution bandwidths (=<100 Hz).They don't give you any FFT settings for those narrow RBW's (i.e. windowing) so it's safe to assume they optimized for the narrow filter to act just like the wider ones only faster than if they were implemented in hardware.

author: xmo
author_rank: Regular Contributor
timestamp: April 25, 2021, 04:08:40 am
content: Also, from: "Fundamentals of Spectrum Analysis"; Christoph RauscherDigital IF filtersNarrow bandwidths can best be implemented with the aid of digital signal processing. In contrast to analog filters, ideal Gaussian filters can be realized.Much better selectivity (SF = 4.6) can be achieved using digital filters instead of analog filters at an acceptable circuit cost.Analog filters consisting of five individual circuits, for instance, have a shape factor of about 10, whereas a digitally implemented ideal Gaussian filter exhibits a shape factor of 4.6.Moreover, digital filters feature temperature stability, are free of aging effects and do not require adjustment. Therefore they feature a higher accuracy regarding bandwidth.The transient response of digital filters is defined and known. Using suitable correction factors, digital filters allow shorter sweep times than analog filters of the same bandwidth.The IF signal after the IF amplifier must first be sampled by an A/D converter.To comply with the sampling theorem, the bandwidth of the IF signal must be limited by analog prefilters prior to sampling.This band limiting takes place before the IF amplifier so that intermodulation products can be avoided, as was the case for analog filters.The bandwidth of the prefilter is variable, so depending on the set digital resolution bandwidth, a very small bandwidth can be selected.The digital IF filter provides for limiting the noise bandwidth prior to envelope detection.

author: Electro Fan
author_rank: Super Contributor
timestamp: April 25, 2021, 08:07:18 am
content: tkamiya, not sure if you have seen this but every time RBW and video bandwidth come up I revisit this to get grounded; your question might go beyond this but just in case....https://youtu.be/Ffhs9Ny03lMI think the posts from xmo and kirill_ka talk to where and how the analog and digital signal processing are applied. I think the practical answer (limitation) is that if you want to have the best most accurate (clearest and low noise) view of signals that are relatively small and close to each other you would tighten the two settings to the maximum extent possible (such as 1Hz RBW and 1Hz VBW) or to the extent needed to accommodate your requirements but at that point you will have also have the slowest sweep time.