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Re: errors of "error" models
2 - @Gary O'Neil, N3GO
15 December 2019 - /g/nanovna-users/message/8238 Hello again, We are terribly sorry but we forgot to emphasize enough that a model such this one is totally unavoidable, because of the technique this very measurement unit uses. Regards, gin&pez@arg |
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Re: errors of "error" models
@Gary O'Neil, N3GO
15 December 2019 - /g/nanovna-users/message/8238 Dear Gary, Not at all. Would you read, please, our related message: #85: On the Formation of a Virtual Port 15 December 2019 - /g/nanovna-users/message/8237 ? Anyway, the fact is that we are looking now for the * l i m i t s * of this model, because we already have interesting experimental evidences on this very subject - * v e r y * interesting indeed, we promised you. Kind regards, gin&pez@arg |
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Re: errors of "error" models
#85: On the Formation of a Virtual Port
Hello, Allow us, please, to somehow explain the formation of a Virtual Port facupov, in our sow. Well, since we can always introduce the "reflection" relation: (beta) = (gamma) . (alpha) between the output ("reflected") and input ("incident") signals at one and the * s a m e * r e a l * port, or equivalently : one and the same real port defines a relation involving the signals "reflected from" and "incident to" it - e.g. in ||05| g :: 1.b = g.a1 || and ||07| G :: 1.b = G.a || at: of: #82' : On The Two-Port Sine Qua Non Practical Application - Source and Load 11 December 2019 - /g/nanovna-users/message/8147 - we thought that we would also consider a -somehow inverse to the above- definition by which the signals at two * d i f f e r e n t * ports, e.g. to the [REFLECTED] and [INCIDENT] ports of HP8502A - #84: On the Virtuality of the "Measurement Port" 15 December 2019 - /g/nanovna-users/message/8225 - could define one and the same * V i r t u a l * -non-real- Measurement Port. By the way, also allow us, please, to strongly re-suggest, to the interested member of this group, the fundamental, sine qua non, paper on the subject of the S-parameters (of this Virtual Two-Port V2P, in our sow) named by Richard H. Hackborn as "errors" in its Work: "An Automatic Network Analyzer System", Microwave Journal, May 1968, p.46 #37 : The [LeastVNA] - 7 October 2019 - /g/nanovna-users/message/4250 Unfortunately, this paper did not openly appear on the Internet, at least at the time we looked for it, that is exactly one year before, on 14.12.2018, so we also suggest to look at a nearby Library, e.g. we found it at the Library of TUV at the bookshelf : . Anyway, we already gave an excerpt of this valuable paper -for fair use, of course- at: #15 : 26 September 2019 : /g/nanovna-users/message/3147 Sincerely, gin&pez@arg :85# |
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Homebrew Female SMA standards and T-Check
A few years ago I made an open and a short female SMA standard for calibrating my HP 8753C VNA (for the load I used a very nice 85052 female 3.5mm load). I never used the open and short above about 30 MHz, so I didn't worry too much about their accuracy.
With my purchase of a NanoVNA I thought I could put them to use in lieu of the male standards the NanoVNA comes with. And so I thought I'd check their accuracy, using my 8753C and the Rohde & Schwarz T-check method. Of course, I had not characterized my standards, and so I thought, as a first attempt at checking them, I would use the "stock" 3.5mm cal-kit definitions that are stored in the 8753C. The key parameters of the "stock" 3.5mm definitions (to match HP's 85033C kit) are: Open: C0 = 53, C1 = 150, C2 = 0, C3 = 0, and Offset Delay = 14.491 ps Short: Offset Delay = 16.695 ps Thru: Offset Delay = 0 ps Much to my surprise, the results were very good, as you can see in the attached T-check plot. But, I wondered, do the "stock" HP delays bear any resemblance to the actual delays of my SOLT standards? Assuming HP's Offset Delays were not the same as my SOLT Offset Delays, why not change HP's "stock" Offset Delays (as defined above) to move the reference plane to the end of my standards (i.e. at the location of the actual open and short). So, as an experiment, I decided to subtract 14.491 ps from HP's "stored" 3.5mm definitions. In other words, o The Open Offset Delay changed from 14.491 ps to 0 ps. o The Short Offset Delay changed from 16.695 ps to 2.204 ps o The Thru Offset Delay changed from 0 ps to -14.491 ps The results weren't quite as good as I expected (see attached T-check PNG). Maybe, I thought, the Thru's delay change needed to be positive, not negative, so I changed its Offset Delay from -14.491ps to +14.491ps. Even worse results! So I tried doubling the Thru's Offset Delay. That is, rather than making it -14.491 ps, make it -30 ps. The results now look pretty good. But why does doubling the Thru delay give these results? And so my questions are: 1. Why did doubling the Open/Short Offset Delay delta of -14.491 ps to be the Thru's Offset Delay give the results it did? 2. Why are the Thru Offset Delays in HP's Cal Kits all spec'd to be 0 ps? (Clearly the length of the thru's are not zero, so what is HP referencing to determine that an Offset Delay is 0?) Thanks for any insight provided! - Jeff, k6jca |
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Re: Cases
Thanks for the reply. I tried eBay and eBay Canada and all that comes up is
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the whole units not just a case for an existing unit. I searched nano VNA case and VNA case. On Sat., Dec. 14, 2019, 19:46 Terry VK5TM, <vk5tm@...> wrote:
Search Ebay, there's plenty of them. |
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Re: errors of "error" models
#84: On the Virtuality of the "Measurement Port"
Hello, Allow us, please, to inform you that since in our sow we see the "Measurement Port" facupov as the Virtual Port of the irreversible, non-reciprocal, two-port V2P [1], at least in the case of the basic HP 8502A Transmission/Reflection Test Set [2], we just uploaded a rather big (2,752 pixels width X 2,060 pixels height), and rather clean, figure of its equivalent circuit of some version of it [3], at: After that, we hope it would be crystal clear the objective fact that facupov this device is * N O T * a TWO-PORT at all, but it is the FOUR-PORT Network : w [RF INPUT] - [TEST] - [INCIDENT] - [REFLECTED]. Therefore, also allow us, please, to inform you that, about 25 twenty- -five years ago, we started our research on this very [anyVNA] subject, by expressing -at least in the "Low Frequencies"- the shown Four-Port as an effective "Error" Two-Port - after a long sequence of assumptions and approximations, of course. Sincerely, gin&pez@arg REFERENCES [1] #77: On the current explanation of full one-port "error" model in our sow - facupov, as always - with an Application to the Measurements of Two-Port Devices : 11 November 2019 - /g/nanovna-users/message/6798 [2] archive.org,HP: 8502A : [3] archive.org, HP: 8502A, p. 5/6 : :84# |
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Re: Increasing measurement range (ohms) ?
On Fri, 13 Dec 2019 at 22:58, <roncraig1@...> wrote:
You are not going to be able to improved reading of high impedance very The best solution is to make a transmission measurement. That allows high impedances to be measured better than a reflection measurement Probably the best thing to improve unit's overall accuracy is the I don¡¯t know the tolerance of the 49.9 ohm resistors, but 49.90000000 ohms is plenty good enough Here are a couple of equations for VSWR that I personally find convenient VSWR=R/50 for R>=50 VSWR=50/R for R <= 50. So for 49.9 ohms VSWR=50/49.9=1.002 You will find it is a 60 dB return loss if you use an online calculator such as; The guaranteed return loss of the loads in my $13,000 Agilent 85052B 3.5 mm calibration kit is 48 dB at low frequencies. IMHO, unless the 49.9 ohm resistors have a poor tolerance, *the difference between 49.9 and 50 ohms is not worth worrying about. * I measured the source match at port 1 using an HP 8720D VNA with 85052B calibration kit. The match is *excellent* - it far exceeds the uncorrected performance of the 8720D. On port 2, the match is poorer, but still quite good. Dave -- Dr. David Kirkby, Kirkby Microwave Ltd, drkirkby@... Telephone 01621-680100./ +44 1621 680100 Registered in England & Wales, company number 08914892. Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United Kingdom |
gin&pez@arg
Dr. David Kirkby, Kirkby Microwave Ltd