Noise Figure Comparison Webinar - Page 1
Forum section: electronics / rf-microwave

author: Joel_Dunsmore
author_rank: Regular Contributor
timestamp: February 08, 2022, 12:25:42 am
content: Not entirely sure this is appropriate for this forum, but I'll be presenting a noise figure test comparison webinar (goes live tomorrow) and will be in the online chat for Q&A. Here's the link below , you will probably have to give an email to sign up. I compare NFA (both old and new), UXA (SA noise figure) and PNA-X for amplifiers, mixers and what to do when your device needs de-embedding. And I touch slightly on noise parameters. It's mostly lab demo to see what things really look like, with a real life comparisons. Oddly for a 60 minute webinar with about 45 minutes of in-the-lab video, it seemed to take me at least 60 hours work to get it done. Anyway, here's the link:https://connectlp.keysight.com/LP=31495?elqCampaignId=19552?utm_source=blog

author: xmo
author_rank: Regular Contributor
timestamp: February 08, 2022, 12:40:08 am
content: Thanks!I think this is an appropriate forum. I believe there are many here who want to expand their knowledge and skills - even though your employer won't sell to us any more.Once upon a time the local rep was more than happy to take my $18,000.00 personal check for an RF test set! He didn't even demand payment before placing the order. Net 30

author: xmo
author_rank: Regular Contributor
timestamp: February 14, 2022, 07:53:28 pm
content: Thanks again for the invitation. I wasn't able to attend in real time but I watched the recording. Nice job!

author: G0HZU
author_rank: Super Contributor
timestamp: February 15, 2022, 12:29:47 am
content: I registered and watched it and it was very good, thanks Joel! The hour went by very quickly.Here's a link to an old Agilent selection guide that describes some of the classic HP/Agilent noise figure meters that were available up until 2008. The cold source method using a PNA-X VNA is included plus there are some performance comparisons in terms of uncertainty.https://assets.testequity.com/te1/Documents/pdf/noise_figure_selection.pdfI've got one of the old 26GHz E4440A PSA analysers here and this is included in the Agilent selection guide and it has the noise figure option fitted along with the 1DS low noise preamp option. See below for an attempt to measure the noise figure of a MiniCircuits PGA103+ LNA with my PSA analyser. This LNA has a noise figure as low as 0.5dB at VHF.https://www.minicircuits.com/pages/s-params/PGA-103+_VIEW.pdfIt was interesting to see Joel use 151 measurement points. I tried this with the PSA analyser after setting the bandwidth to 4MHz. The plot below has no averaging and the result looks quite close to the datasheet. I used an Agilent 346A noise source with the PSA analyser. The measurement time is quite slow when set to 151 points. I usually set the PSA to 31 points and usually leave it set at the default 296.5K.

author: Joel_Dunsmore
author_rank: Regular Contributor
timestamp: February 15, 2022, 01:13:28 am
content: Quote from: G0HZU on February 15, 2022, 12:29:47 amThat was a very good overview, and mostly holds true today, but of course UXA replaces PXAQuoteThe 151 points was to get exactly 1 point every 100 MHz, and I wanted enough point density to show the ripple in the measurement due to mismatch effects. Your 31 points across 3 GHz is essentially the same spacing. Particularly at low frequency where mismatch is small, the Y-factor does a very good job. It would be interesting to see on your device if the noise figure is really going up of it is just not matched well anymore at higher frequencies: the NF_min would tell you that.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: February 15, 2022, 03:21:06 am
content: I'm new to noise measurements. Is the distinguishing feature of a noise receiver that it switches in multiple impedances?

author: Joel_Dunsmore
author_rank: Regular Contributor
timestamp: February 15, 2022, 05:04:45 am
content: There are a few things that distinguish noise receivers:1) of course, very low noise figure2) Typically switched gain states to handle a wide range of noise powers3) Some type of filtering so that out-of-band noise doesn't fold back into the noise detector. This last is often accomplished with a Yig-Tuned filter (on SA), but on the PNA it is done with switch filters that reject the 1/3, 2x and 3x frequencies of the input signal so that noise in those regions don't convert to the the noise detector (typically happens at LO*3, LO/3 and LO*2 freqeuncies.

author: xmo
author_rank: Regular Contributor
timestamp: February 15, 2022, 03:40:25 pm
content: "I'm new to noise measurements. Is the distinguishing feature of a noise receiver that it switches in multiple impedances?"If I understood the webinar, I would say that most instruments used to measure noise figure do not switch in multiple impedances.The test ports of instruments used to measure noise figure - noise figure analyzers, spectrum analyzers, and network analyzers - although intended to be 50 ohms, aren't perfect. Their actual characteristics are measured with S-parameters. In the PNA-X, these parameters are used to control an impedance tuner in order to provide a better match to the DUT, thereby enabling the instrument to produce results that have less uncertainty than earlier instruments.To learn more, read Keysight Application Note: 5990-5800 High-Accuracy Noise Figure Measurements Using the PNA-X Series Network AnalyzerFor a comparison of noise figure measurement with various instruments, see: 5989-8056EN Agilent Technologies Noise Figure Selection GuideAlso, there are several general application notes in the AN57 series from HP - Agilent - Keysight that explain noise figure basics.

author: Joel_Dunsmore
author_rank: Regular Contributor
timestamp: February 15, 2022, 04:42:18 pm
content: Quote from: jjoonathan on February 15, 2022, 03:21:06 amsorry, I forgot to address the last question. As far as I know, there are no other instruments besides the PNA-X which have built-in impedance tuners. All NFA and SAs using Y-factor don't provide any DUT port 1 connection (other than the noise source that is; the impedance tuner for noise figure is always on the DUT input side) and so don't have any chance to change impedance. Some very old noise-parameters test systems used mechanical tuners with SA, but those have all been replaced with using PNA as a receiver. In fact, that's one of two major differences between PNA and PNA-X: only PNA-X can have the noise receiver (at port 2) and the internal impedance tuner (at port 1). the second big difference is PNA-X has 33 bands of sub-octave switched filters to provide very low harmonics of the source at the output, needed to do harmonic testing and high performance IMD testing.

author: xmo
author_rank: Regular Contributor
timestamp: February 17, 2022, 05:08:17 pm
content: Understanding noise figure and the measurement of noise figure is an important RF skill. That's why a webinar like this is so helpful.I have worked in the public safety communications field for many years. Optimizing receive performance relies on understanding noise and noise figure..My most recent project was to formulate rules for in-building coverage enhancement systems operating in our service area. These systems often employ signal boosters (bi-directional amplifiers) While researching these devices, I located test reports for several units. The FCC has rules governing signal boosters. The documents I found were published results of reports that have been submitted to the FCC for certification of these devices.I have attached an image containing pieces of one report. I have omitted the name of the testing entity as my intent is simply to show that noise figure can be difficult to understand - even for professionals. The test results clearly indicate that the engineer has no clue about noise figure. Obviously, there are two issues - failure to recognize an invalid result and the procedural error that led to that result.It is incomprehensible to me how a commercial testing entity in the business of preparing FCC certifications could make such a mistake! Even if inexperienced junior engineers are assigned to test these units, you would think that a senior person would review the document before submission to a federal agency.Additionally, why did the engineering staff of the equipment manufacturer not catch this?

author: xmo
author_rank: Regular Contributor
timestamp: February 18, 2022, 06:08:04 pm
content: In the webinar, Dr. Joel presented a comparison of noise figure measurement methods and instrumentation starting with an early NFA and culminating with the awesome PNA-X. To fill in our understanding, there are a couple other methods to consider.First, there is the direct method as employed by the test lab in my previous post. This method is simple and OK for cases where the noise figure is relatively high and results are only needed at a single frequency.Also, there are noise figure meters. The HP 8970 noise figure meter was the industry's gold standard back in the halcyon days of Hewlett Packard B.C. The basic instrument was limited to 1600 MHz but you could extend its capability to 26.5 GHz with an 8970S system comprised of an 8970B noise figure meter, an 8971C noise figure test set, and an 83630B synthesized signal generator. You could also add an 8757 to give a CRT display of measurement results and an HP pen plotter for hardcopy. That would have been THE hot ticket 25 years ago.Anyone who has used an 8970 understands that its user interface is - how shall we say? Complex? Arcane? Inscrutable? Keep the manual with the instrument at all times? All of the above! The NFA basically took the 8970 capability and added a modern user interface.It would have been very interesting to see how the results from such a system compare to the modern methods but I am sure that none of those instruments are anywhere to be found at Keysight.

author: G0HZU
author_rank: Super Contributor
timestamp: February 18, 2022, 09:35:26 pm
content: It's many years since I last used an 8970B. You should really use one in a screened environment or at least keep the noise source and the DUT in a screened enclosure during the testing. Otherwise there's little to warn the inexperienced operator that external signals are corrupting the 8970B measurements. The same applies to the modern instruments but at least you do get a stepped frequency display on the modern instruments so it's easier to spot frequencies where there is noise pickup. This happened to Joel in his video but he was able to diagnose the problem.The 8970A (and probably the B) uses a BJT based current source at the IF to feed the noise signals to a compensated diode detector. This works much better than it might first appear, but the modern instruments use a digital IF to measure the noise and this should be a bit better. The 8970B is also stuck with a fixed 4MHz detection bandwidth.The other niggle I found with the 8970B was that it sometimes struggled to calibrate up towards the top of its frequency range when using a 5dB ENR noise source that was in the region of 4.7dB to 5dB ENR. I think the 8970B noise figure was too high for a noise source with an ENR this low. At work there were several HP 346A noise sources left sulking in a drawer because they had a slightly lower ENR than the 8970B could cope with.My PSA analyser is a good all round compromise and it also has a digital IF. The LF to 3GHz internal preamp has low VSWR and a low noise figure even below 10MHz so this makes it stand out against the alternative analysers if you need to measure noise figure below 10MHz. It also has a user selectable detection bandwidth from several MHz down to 1Hz although anything below 100kHz BW means the system becomes painfully slow.At some point the company I work for might hire or buy a modern PNA-X and it would be really interesting to try out the cold source method.

author: xmo
author_rank: Regular Contributor
timestamp: February 18, 2022, 10:01:39 pm
content: Here are a couple interesting slide about the PNA-X that I snipped from a presentation they did at a microwave symposium.