How to build a do-it-yourself vector-network analyzer that’s actually useful - Page 1
Forum section: electronics / rf-microwave

author: Free_WiFi
author_rank: Regular Contributor
timestamp: July 19, 2018, 07:21:40 pm
content: no comments ...

author: Free_WiFi
author_rank: Regular Contributor
timestamp: July 19, 2018, 07:23:14 pm
content: It's expensive like a kidney,it's not opensource and they claim that's an DIY projectJust LOOOOOL.

author: CopperCone
author_rank: Super Contributor
timestamp: July 19, 2018, 07:37:08 pm
content: Whats wrong with this?How much work do you think is going to get done in a university laboratory? You get a RF schematic, so that would mean you probably need to make the cables (good skill), lay the thing out/do minor mechanical work, then do calculations on the spans/signal levels to develop boundaries..We did not even have functional chips or breadboards at my university. College kids won't be laying out RF pcb's if you just want to teach a basic class.. that would drive the instructors completely insane and manufacturing would be hard.You probably learn things like how to plug in the components to an existing VNA to categorize them and other good skills, a good instructor can make this thing work and it can be modded. The highest frequency I worked in university was about 10MHz for a good couple of hours making a fast discrete logic gate out of a ton of transistors, and I was basically told 'this won't work right because its on a bread board'. None of the RF classes even had a laboratory component, smith charts were basically uninteresting.It does seem like most of the effort would be in writing the program though.It does at least look cool, it feels like you are working on something interesting and important. This is important towards keeping people interested and not just beating them with some kind of field equation. An instructor can also say alot about it, stories, etc...

author: Free_WiFi
author_rank: Regular Contributor
timestamp: July 19, 2018, 07:54:03 pm
content: This is PURE PILPILISM,you are talking to the wind.....However....this project is aimed to teach,so if it's intended for that purpose then why it's not opensource?why they are trying to pass this bullshit like an opensource project if it's not ....lol.

author: ogden
author_rank: Super Contributor
timestamp: July 19, 2018, 08:56:00 pm
content: Quote from: Free_WiFi on July 19, 2018, 07:23:14 pmWhich part of "DIY for universities" you did not understood? If you expect that Minicircuits will give away their quality microwave components for free - relax. Coupler alone is 260$ worth. If you want "el-cheapo" opensource VNA, then look somewhere else.

author: Free_WiFi
author_rank: Regular Contributor
timestamp: July 19, 2018, 09:08:29 pm
content: Quote from: ogden on July 19, 2018, 08:56:00 pmIn the video they're saying that this "DIY" is not only for universities,but also for students....So i don't pretend nothing,just too much Bullshit Speech around.

author: ogden
author_rank: Super Contributor
timestamp: July 19, 2018, 09:29:15 pm
content: Quote from: Free_WiFi on July 19, 2018, 09:08:29 pmYou are too occupied with "and students" part of marketing presentation that you can't see anything else in it? Look at Minicircuits offer from universities point of view. It's bargain compared to "proper 6GHz VNA". In case you are poor student who can't afford 2500$ VNA for MIT classes, then maybe reconsider your occupation? Agriculture perhaps?

author: Bud
author_rank: Super Contributor
timestamp: July 19, 2018, 09:31:06 pm
content: I bet the SMA wrench alone will cost a hundred buck. Nothing is cheap at Minicircuits.I donot know where the title came from but it is controversial at least. There are many DIY designs that ARE useful in their design frequency range, all of them in fact. The older guy in the video should get a life.

author: ogden
author_rank: Super Contributor
timestamp: July 19, 2018, 09:34:20 pm
content: Quote from: ogden on July 19, 2018, 09:29:15 pmThere are lot of seemingly way too expensive products around. So what? Just buy something you can afford and don't whine.

author: Bud
author_rank: Super Contributor
timestamp: July 19, 2018, 09:35:17 pm
content: And by the way, while the demonstrated contraption may be useful, it is the Least Practical design i have ever seen. You need a power supply for it (guess a bench one will be recommended). , it takes a wack of space on the bench, you can't take it to the field or on the roof, etc. Oh yeah, they omited cost of a calibration kit on purpose.

author: ogden
author_rank: Super Contributor
timestamp: July 19, 2018, 09:39:23 pm
content: Quote from: Bud on July 19, 2018, 09:35:17 pmMost of university lab contraptions are not practical for field useYou shall get a life as well

author: wraper
author_rank: Unknown
timestamp: July 19, 2018, 09:52:19 pm
content: Quote from: Bud on July 19, 2018, 09:35:17 pmWhy the hell do you even assume it is supposed to be taken to the field? It's a learning platform and also could be used as development platform. Hobbyists and normal VNA users certainly are not the target audience.

author: hendorog
author_rank: Super Contributor
timestamp: July 19, 2018, 10:00:02 pm
content: Quote from: Bud on July 19, 2018, 09:35:17 pmActually the Cal kit is included. It looks like its USB powered.https://www.minicircuits.com/pdfs/UVNA-63.pdf

author: drew23
author_rank: Contributor
timestamp: July 19, 2018, 10:01:06 pm
content: There is more information available. The kit costs around $2500 and will be shipping in September. No mention of code availability. It is list as a first project, so there may be more to come. The transceiver board seems very capable.https://www.minicircuits.com/WebStore/uvna_63.html

author: Bud
author_rank: Super Contributor
timestamp: July 19, 2018, 10:02:04 pm
content: Because the title says "....actually useful". I have my interpretation of the term "useful" affer 35 years in RF.

author: wraper
author_rank: Unknown
timestamp: July 19, 2018, 10:08:10 pm
content: Hmm, that chip on the PCB is 3D RF imager... The same as used in Walabot.

author: Sparky49
author_rank: Regular Contributor
timestamp: July 19, 2018, 10:09:44 pm
content: I buy a couple of tins of paint and some wood panels to do some diy in my living room. I don't expect the paint manufacturer to give me the ingredients and procedure to recreate the paint from scratch, and I don't expect the wood manufacturer to tell me how to grow my own trees. Yet I spend a bit of money to buy the items to perform diy.It's the same here. Minicircuits are providing a kit, which can be assembled together yourself, if you pay for it. Why does it need to be open source when they aren't calling it open source? They are providing a kit for a niche market, which the vast majority of electronic hobbyists are not included. This isn't uncommon. Terasic sell dev kits for thousands of dollars. So do many other manufacturers: microchip, linear, etc. Most are far overpriced and are not intended for hobbyists.This is firmly aimed at the university market, for the use of (not purchase!) students and possibly researchers. It is not very practical, but it is not intended to be a great VNA, its a relatively cheap, complete kit for universities to buy. Universities by and large don't wince at such price tags, as they will have budgets to spend and the real deal is the time it saves in preparing work for students. If I was a prof working on some interesting labs for my students, buy several of these kits might be quite appealing as I don't have to waste time researching all the bits and ensuring they will work myself. This is often the primary selling point, and where it is actually "useful", though I do sometimes wish things weren't quite so expensive.Sometimes the bean counters are wrong, but if the product is a flop for its chosen target market then we might see it withdrawn

author: Free_WiFi
author_rank: Regular Contributor
timestamp: July 19, 2018, 10:17:38 pm
content: If this kit is not opensource,then how can you pretend that students will learn something from this "EDUCATIONAL DIY"?

author: wraper
author_rank: Unknown
timestamp: July 19, 2018, 10:35:37 pm
content: Quote from: Free_WiFi on July 19, 2018, 10:17:38 pmHow do students learn by using non opensource oscilloscope? How dare people use Raspberry pi in their DIY projects? Hardware is not open!!! Students learn principles how VNA works using some level of abstraction. It's not like they could make their own board even if they had full schematic and gerber files.

author: CopperCone
author_rank: Super Contributor
timestamp: July 19, 2018, 11:01:19 pm
content: Did you guys have like billion dollar university laboratories or something that you are complaining about layers of abstraction with this beast?Did anyone here actually do anything more then a breadboard with low frequency stuff and maybe a MCU on it at university apart from independent research projects that you need to beg the department to allow you to do for credits? The most advanced RF project I saw for undergraduates at my university was some kid designing op-amp active filters that work at some where like 30MHz @ low signal power levels.. he got access to a spectrum analyzer and a few hours training. I think a few classes used zig-bee's you can shove on a breadboard for some control systems stuff. You had to be friends with the laboratory people and proven responsible to even be allowed near the spectrum analyzer.Maybe graduate students do it more...I think where I went to school they would scratch the labels off the mini-circuits boxes so people don't steal them.

author: hendorog
author_rank: Super Contributor
timestamp: July 19, 2018, 11:07:46 pm
content: DIY in this case refers to DIY implementation of the VNA equations. I.e. work out the code to implement the equations which you have derived in your study.They mention Matlab (or was it Labview) and Python for doing so.

author: chris_leyson
author_rank: Super Contributor
timestamp: July 20, 2018, 12:54:07 am
content: If you want it cheap and 6GHz then go go build thishttp://hforsten.com/cheap-homemade-30-mhz-6-ghz-vector-network-analyzer.htmlIf you want it really easy to build then get the minicircuits design.If you want to build a DIY 6GHz VNA then at least make an effort to understand the principles and practicalities involved. Any serious practicing RF engineer wouldn't bother wasting time building a spectrum analyzer let alone a VNA. Maybe you should do some more background reading into wideband RF design and then you might understand the difficulties involved. Maybe this should have been posted in the beginers section.

author: drew23
author_rank: Contributor
timestamp: July 20, 2018, 02:23:02 am
content: Mini Circuits webpage says "access to free online tutorials and sample code, coming soon". I think the page came up in the last few days. The support materials may be useful. Shall have to wait and see. It would be good if the TRX board were available separately.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 20, 2018, 04:40:29 am
content: its more proper to say it a "modular" or "educational" VNA. well i'm feeling lucky to get a "ready working"VNAfor more BW and accessories and alot lesser price tag, no need to diy build myself stuffs. it has quirks but thats what a students sector for to build equations and diagnosis the trouble to enhance knowledge bla bla.. good luck getting a good coupler respond if you are going to build one. you need a VNA to build a VNA...

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: July 20, 2018, 04:48:20 am
content: Free_WiFi, you seem to have little grip of what matters in teaching.You want to teach one step at a time - in this case they can start by building it by themselves, which gives them some practical experience most students don't have during their university career (microwave components are just too expensive). The software is the key here - this would be an amazing project to have students implement the actual equations to go from signal levels from a few power sensors to transmission/reflection, and to learn different calibration algorithms. And because everything is built out of blocks, a more advanced and larger team project could then allow them to design their own PCBs for the couplers and that will give them some experience there too.This is a great thing, and I am excited to look at getting our hands on one to see if we can integrate it in the coursework I will teach next semester. If you feel like you can do it better, that is good for you, and I wish you the best of luck. Nobody said it has to be a very high quality VNA, it has to be a teaching tool. But it does seem to do an amazing job in finding the balance between modularity, flexibility and effort that needs to be done for a teaching tool.And regarding open-source: As long as they have a good driver, I'm happy. I don't feel a need to go write my own, or have the students write their own - it is clearly not the subject this kit will try to teach.

author: ogden
author_rank: Super Contributor
timestamp: July 20, 2018, 08:50:18 am
content: Quote from: CopperCone on July 19, 2018, 11:01:19 pmWhy it is so hard to believe that many tech university (research) labs are packed with expensive equipment? Just example:http://www.myfab.se/Chalmers/Resources/Alltools.aspxQuote from: chris_leyson on July 20, 2018, 12:54:07 amItbarelyworks in 2..3 GHz range, that's it. You are advised to read conclusions chapter at the end.

author: hendorog
author_rank: Super Contributor
timestamp: July 20, 2018, 09:17:06 am
content: Quote from: ogden on July 20, 2018, 08:50:18 amPerhaps some better advice would be to read about the latest version:http://hforsten.com/improved-homemade-vna.html

author: ogden
author_rank: Super Contributor
timestamp: July 20, 2018, 10:05:13 am
content: Quote from: hendorog on July 20, 2018, 09:17:06 amVery good advice indeed. Improved version looks much better. Thanx

author: LaserSteve
author_rank: Super Contributor
timestamp: July 20, 2018, 12:18:49 pm
content: I work at a university. Mini-Circuits can be quite generous to schools who can make a justification for a discount. Since they get bombarded with requests, they screen the requests very carefully. Their founder/president/management want to ensure their program makes an impact.I have actual experience with Mini Circuits academic discount program, in my case Doppler tracking using a low phase noise microwave oscillator. Three words: "Thanks Mister Kaylie!" Your looking at the public, list, price. The academic price will be less, but it is negotiable based on student impact.Free sample parts /massive hardware donations for academics pretty much disappeared after tax law changes in the late 90s, early 2000s. At best we get 15,20, or 50% discounts on small quantities of items. Often we actually pay higher then consumer prices for a variety of reasons related to liability, and the extra paperwork a vendor has to do to sell to the State. The exception is software, we get seat licenses for some really nice code for next to nothing.I start doing massive extra paperwork at the 1500$, 5000$, and over 20,000$ levels. Instruments over 20,000$ may need a year and a half of approvals from outside agencies, and require bids. So you want a very specific thermal camera that only is made by one vendor? Well a sole bidder is NOT allowed at that 20K$ level.. Leads to very long meetings, especially if there is no other bidder. My corporate friends just whip out a payment card for stuff like that, and place the order.In the US, academic hardware funding is way down the past four years. I'm doing more of "Make due with less" and repairing ancient stuff.Nothing dead goes off the loading dock unless I, or the machinist strip it for useable parts.What a grad student needs and what goes on a hobbyist bench are usually two DIFFERENT things. I have a habit of trying to go "cheap" as often as possible as funding is scarce and the competition for funding is massive. But often times we need peak performance and high resolution. Graduate students are very costly and expensive employees who work 60 hour weeks.Undergraduate instruments have to be built better then mil-spec and bad user interfaces or glitches are intolerable. Often I have 60 students in a lab with just two TAs, so the gear has to be good, as a TA can usually only help one small group at a time. Some of our undergrad labs run for 7 TWELVE HOUR days, and every minute of lab time is used. If they do not have good results in the first lab, they will have problems in the next lab in the series, and it will ripple through the whole semester. (Chemical Engineering in my case)Undergrad EE students, yeah. you can buy them cheap stuff off Amazon as it's a learning experience for them. For undergrad students in other majors, the instruments are often thought of as little more then a needed annoyance, (by the students) as much as I'd and the Professors would prefer they do deep learning about instruments and their limitations. We do have limited time in a semester, and nearly every waking moment is used for education if you have good instructors. Thus we need to make some tradeoffs in what is taught and what is experienced in the lab.That board is designed for education, and guess what, some times we DELIBERATELY make compromises / faults/quirks in the design so that learning occurs. Some of our labs are impossible to complete by design, just to see how the final report reads, and to get students to ask questions/think.MY day job is "Senior Technician, Instrumentation" for 137 grad students and about 300 undergrads... We're not allowed to have financial roll-overs, and if we don't spend it, we may not get the same funding the next year. So we really work to see that tax payer money is carefully spent. My work lab is very sparse compared to my home shop. We only buy parts we need, I have almost no stock parts or spares at work.I measure heat shrink tubing in Dollars per Inch, for example.I've more then once heard, "Steve, I need a little more Nyquist in your design, cut the sampling rate please". Only to turn around and hear "I need to measure fementofarads to track a droplet passing down a filter medium" in the next meeting.BTW, on average fifty percent of the grant is taken for overhead by the institution, world wide. Get a 250,000$ grant, only to have just 125,000 to spend.Steve

author: bd139
author_rank: Super Contributor
timestamp: July 20, 2018, 12:23:34 pm
content: Quote from: hendorog on July 20, 2018, 09:17:06 amDidn't even notice that. Thanks for the link!

author: Sparky49
author_rank: Regular Contributor
timestamp: July 20, 2018, 12:43:53 pm
content: Some good replies from people who understand the target market this is aimed at. Most people in a university lab won't have spaces crammed with billions of dollars worth of equipment, but things quickly add up. My research group is tiny in terms of the number of people, but over the years has built up an impressive set of test equipment including GTEMs, reverb and anechoic chambers, VNAs etc. What often happens is you are giving a fixed-size grant from some source to perform some work. This can range from 10's thousands to a couple of million. However, all that money _has_ to be spent, and unfortunately not on whiskey and beer.So what happens is you end up with a thousand or two left over in the pot at the end of the project, which gets absorbed into uni accounts if you don't spend it. More incentive to buy _something_ which might be useful later in the line.It might seem wasteful (I get frustrated with it myself), but if you don't spend it all, the uni will often reduce your funding in the next round because you were so 'resourceful' in the last.One guy I know in another group bought a 4 port Keysight VNA to measure the impedance of something at 1MHz... I was so jealous...

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: July 20, 2018, 05:23:26 pm
content: Quote from: Sparky49 on July 20, 2018, 12:43:53 pmThat reminds me of something that happened in my group. Professor storms in: "Guys, we had to spend some money... I hope one of you can use a wafer thinning grinder?"My university is lucky enough to have a lot of money coming in from industry cooperation projects. As a result, we have less issues with funding, and have a healthy cashflow.

author: chris_leyson
author_rank: Super Contributor
timestamp: July 20, 2018, 07:31:19 pm
content: @ogden I was was too harsh in my criticism and you're right I should have read about the improved version. Actually I managed to have a quick read today and I'm really impressed with the results, the performance is a hell of a lot better primarilly due to the use of resistive bridge couplers.

author: CopperCone
author_rank: Super Contributor
timestamp: July 20, 2018, 07:53:28 pm
content: Quote from: ogden on July 20, 2018, 08:50:18 amYea my university had seriously hardcore shit forresearchersthat don't need to learn how to make a VNA. Students got jack and shit that left the physics department in 1965. I felt like a peon going to visit french royalty in those laboratories. That list you have has a sputter machine. I think anyone that touched a sputter machine where I went to school would just go missing. People setup independent guarding of their expensive equipment with cameras. You needed to be a graduate student assisting the professor to do anything with that stuff. This VNA thing can be taught 2-3rd year as part of a wave theory class and actually be relevant. The one where you need to do calculations on things like stubs, admittance, etc.My idea would be to make a wave theory class (typically taught) and teach this thing as a lab class that is recommended to be taken in parallel or afterwards. I'm not sure if the frequencies are high enough but having a bit of 'art' in the department to do things like cut out your own filters would a exacto blade would be a breath of fresh air, even if its really simple stuff.. otherwise you just memorize it for a test and forget it afterwards thinking that you will never see it.I always felt like the physics labs that I took were more fun then the electrical labs, because you had to use IC's or manufactured transistors and I never really felt the same magic as you get playing with lens, vacuum pumps, big open coils, etc.If you don't know much about component level problems in electrical engineering like resistor drifts, power ratings, parasitics.. it becomes very sterile and almost beurocratic like programming. I think looking at stuff with a VNA from the start could help people get more of a mind set that 'everything has its little quirks'. I think thats important for anyone to know.

author: LaserSteve
author_rank: Super Contributor
timestamp: July 21, 2018, 02:32:25 am
content: Coppercone,While we can't do it for everyone, come to my beloved College where I work. Show some interest in our Pro's instruments and labs, and you might be surprised. Such interest often leads to paid summer work.Just a camera on the entrances and student work area. No where else.Plan on working next to a few high school students on summer internships as well. If the research works, expect to see your name on the paper, too. Please expect to use the instrument you drooled over. Expect to have a desk in the student office space for the duration of the stay.Expect to learn about weekly group meetings. Then have to defend your work.In the US, involving ugrad and high school students opens a Prof up for outreach funding, and a better chance of grants.When I was a student I drooled over the laser lab thru a four inch window.Now these days I would be invited in.In fact I've been in, like 20 years later.Did I mention the Rocketry, Robotics, Baja Racing, Mini Formula One teams?All of whom get some decent gear.Also expect to do one mandatory semester long, paid, corporate internship, your Junior year. Expect to probably travel out of state for the experience. Then have the option for a second one Senior year. Things have changed for the better in some respects.Steve

author: Beamin
author_rank: Super Contributor
timestamp: July 21, 2018, 04:21:55 am
content: That's not DIY.Plus I think my 5'3" ass could beat up both those guys. Who is the target market DIY'er?

author: hendorog
author_rank: Super Contributor
timestamp: July 21, 2018, 04:49:11 am
content: Quote from: Beamin on July 21, 2018, 04:21:55 amAlready answered.QuoteHere is a link for the simple one port stuff:http://www.vnahelp.com/tip20.htmlAnd this one goes a bit further:http://emlab.uiuc.edu/ece451/appnotes/Rytting_NAModels.pdfThe implication of all this is that it isn't _that_ hard to design a decent VNA, because the maths can correct for many of the hardware issues.And of course there is now open source software available with all of the equations implemented.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: July 21, 2018, 05:11:07 am
content: Quote from: hendorog on July 21, 2018, 04:49:11 amFor some definitions of ''decent'', yes(I recall some people having a lot of issues with drift in one of the cheaper USB VNAs on the site...)Quote from: CopperCone on July 20, 2018, 07:53:28 pmOne of the reasons for this is because those tools are still very fragile if you don't know what you are doing. I actually just received an attenuator that was damaged because someone didn't know you should hold on to both the cable and the attenuator when you tighten down the nut on the SMA connector, and as a result one of the center contacts of the female connector on the attenuator got torn off when the connector started spinning. Sure, this attenuator is not quite as expensive as a full VNA, but still costs more than a entry-level Rigol scope, and is now useless.Something like the minicircuits kit discussed here gives students more hands-on experience without risking damage to some very expensive kit. It being only up to a few GHz also means you don't need to have the very expensive and fragile connectors that most big VNAs come with.And the real issue is not the cost of the actual damage - it is the lost time. All of our VNAs (and my university EE department has a good number) are pretty much constantly booked for measurements. Losing one for a week or two because it has to go out and be repaired would set back many measurements - likely more expensive than the repair of a connector. Oh and we have an old 50 GHz spectrum analyzer that gets it's first mixer blown out on a yearly basis because someone fails to see the "Max 0 V DC" warning label on the front...We actually purchased a good bit of entry level kit for the students a while ago, but not yet a VNA... This might be interesting to look into. We give students their own kit because that way we don't need to risk planning issues, it just makes everything easier. And unfortunately VNAs are just a tad expensive for that.QuoteYou can definitely do interesting microwave networks at the frequency this can measure. I have myself designed and tested some distributed filters at 2.4 GHz.I can't comment on your approach of the labs since where I work the classes are different (we don't have many "lab" courses, most of our courses combine the two). But I can see how this could complement one of those courses very well. I would say that it might be more interesting to stick to the VNA part itself, and just building the math involved, as this is a good exercise in thinking in S-parameter blocks. Adding to it a number of actual circuit design classes likely takes too long, but only experience can tell for sure.

author: ogden
author_rank: Super Contributor
timestamp: July 21, 2018, 05:23:16 am
content: Quote from: TheUnnamedNewbie on July 21, 2018, 05:11:07 amYou can permanently putDC blockon SA that is subject to careless use. Yes, there are some drawbacks but perhaps your application could be fine with them.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: July 21, 2018, 06:16:20 am
content: Quote from: ogden on July 21, 2018, 05:23:16 amYeah, I don't know why they don't or what is going on there (it is not one of my group's SA's, so I only hear about it when yet another researcher blew up the front end)

author: hendorog
author_rank: Super Contributor
timestamp: July 21, 2018, 10:18:55 am
content: Quote from: TheUnnamedNewbie on July 21, 2018, 05:11:07 amAgain, already answered in that thread. The drift is because those VNA's do not implement a reference receiver.This is quite easy to do, and costs next to nothing - just have a look at the Siglent implementation.Why did those cheaper USB guys not do it? Beats me, its easy _and_ cheap.

author: Sparky49
author_rank: Regular Contributor
timestamp: July 21, 2018, 01:33:40 pm
content: Quote from: Beamin on July 21, 2018, 04:21:55 amWhat on earth does your ability to beat up two people have to do with the VNA? Have you ever thrown a hissy-fit because when you buy some paint to decorate your living room (DIY) because the manufacturer didn't release the procedure to make the paint yourself?The target market is probably someone who (amongst other things) can read through a page of a forum thread.

author: wraper
author_rank: Unknown
timestamp: July 21, 2018, 02:11:54 pm
content: Quote from: Beamin on July 21, 2018, 04:21:55 amSomeone did not watch or listen what was said in the video, nor read this thread.QuotePlus I'm pretty sure police will beat up your ass with taser and put you in jail. One of the stupidest and most irrelevant comments I've read on this forum.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 21, 2018, 04:13:02 pm
content: Quote from: hendorog on July 20, 2018, 09:17:06 amLooks like some nice work.I thought the original video was decent. Puts the basic blocks together and write the software for it. I rolled my own software and agree that if you were a student learning RF, this would be very good exercise.

author: Beamin
author_rank: Super Contributor
timestamp: July 23, 2018, 04:07:29 am
content: Quote from: hendorog on July 21, 2018, 04:49:11 am

author: hendorog
author_rank: Super Contributor
timestamp: July 23, 2018, 07:41:42 am
content: Quote from: Beamin on July 23, 2018, 04:07:29 amDid you bother to read the quote immediately after that comment? No, you didn't, because you were too busy looking for something to get angry about.Mine was the most helpful response you got. Everyone else just told you top pull your head in. So my mistake.Pull your head in.

author: mmagin
author_rank: Frequent Contributor
timestamp: July 23, 2018, 11:03:35 pm
content: Quote from: Free_WiFi on July 19, 2018, 07:54:03 pmWhat is pilpilism? My dictionary does not have that word.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 23, 2018, 11:20:35 pm
content: When you feel like eating shrimphttps://www.spainfoodsherpas.com/pil-pil-prawns-recipe/

author: Free_WiFi
author_rank: Regular Contributor
timestamp: August 02, 2018, 01:53:00 am
content: There is a guy,which told me something like this : "to make an VNA you need another VNA ......."At this point if this is true or was,then how the first VNA was born ?LOL

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 02, 2018, 03:20:53 am
content: They use some 'tricks' only the ultimate creators know...

author: xaxaxa
author_rank: Regular Contributor
timestamp: August 02, 2018, 03:22:54 am
content: Quote from: Free_WiFi on August 02, 2018, 01:53:00 amI don't think that's really true; you can easily construct 1-port or 2-port devices with known characteristics, for example shorting out a board mount sma connector with a big blob of solder will give you almost ideal short up to 4GHz, and soldering 2 0603 100ohm resistors to the connector (after grinding off the pins) will get you a decent 50ohm reference with return loss >30dB. I didn't have access to a "real" VNA when I built mine.

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 02, 2018, 05:37:59 am
content: Quote from: xaxaxa on August 02, 2018, 03:22:54 amand how do you come to know all that? see below...Quote from: xaxaxa on August 02, 2018, 03:22:54 amthen you must have the 'tricks' or at least one 'another tool', a spectrum analyzer maybe? btw, i can bode (respond) plot something out of FG and a DSO, no need an SA...why it is said you need a VNA to build a VNA because thats the most convenient around today. its not necessary means you 'really' need the VNA first place. multi GHz VNA are in existence to build lower grade VNA (pcb characterization, sure you can do with a SA w tracking gen of higher grade), then why use archaic or physics or whatever troublesome method? do you consider a full solder blob on a SMA usefull or practical? good luck building a VNA pcb empty handed from scratch...

author: hendorog
author_rank: Super Contributor
timestamp: August 02, 2018, 05:40:15 am
content: It is useful because it is one of the three standards you need. The other two are an open and a load.With those three characterised standards then you can build a vna.With physics you can characterise three standards from first principles.So yes, you can build a vna without another vna.

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 02, 2018, 05:46:57 am
content: if first principles and SOL is all that required, the guy who made the diy VNA should already come out with something usefull by now on the pcb version 1. then again, how do you get a good SOL kit?

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: August 02, 2018, 06:02:36 am
content: You don't need SO(T)L to do the calibration. In fact, SOTL is not really a good calibration method outside of lower-frequency (few GHz) applications. We almost always calibrate our systems with TRL, as this does not require perfectly known standards. (Don't ask me about the math though, as I'm not that familiar with it either). The issue with TRL at lower frequencies is that the line becomes large.Right now, from what I have been told, the difficult part making a high-end VNA is not getting the performance in the first place - it is stability and speed. Keeping that performance right there within a fraction of a dB for many hours or days, and allowing fast measurements to be done to better characterize the system. And don't think this is just something needed for production test - colleagues of mine working on microwave for biomedical and spectroscopy applications sometimes do measurements that take 72 hours (as they need to determine how a parameter changes as a yeast culture grows, for example). As such, they need that stability over time to ensure that they are not measuring the VNA drift but actually measuring the DUT.The beauty of a VNA calibration is that (to some extent at least) the performance of the VNAs components doesn't matter that much - you calibrate that out anyways. Of course, you run into limits of dynamic range and return loss - if your output connector on the VNA has an S11 of -15 dB, good luck measuring the S11 of a device that should have extremely low return loss...

author: hendorog
author_rank: Super Contributor
timestamp: August 02, 2018, 07:19:22 am
content: Quote from: TheUnnamedNewbie on August 02, 2018, 06:02:36 amI agree completely.The point being that the VNA doesn't define any standards, it just needs to be stable enough that you can compare your reference standards - whatever they may be - with the thing you want to measure. There is no absolute accuracy in a VNA. This is different to a spectrum analyser.This is why it I think is theoretically easier to build a VNA from scratch, than build a Spectrum Analyser.The SA needs to be calibrated so that it knows where 0 dBm is with high accuracy.The VNA just needs to be able to compare two things with high accuracy.

author: Free_WiFi
author_rank: Regular Contributor
timestamp: August 02, 2018, 03:33:39 pm
content: I want to make this question.Is it possible to make an VNA from zero by having only a good Scope and wide knowledge of advanced math?

author: tautech
author_rank: Super Contributor
timestamp: August 04, 2018, 11:25:02 pm
content: Swatting up some for the new Siglent SVA and a couple of docs that offer some VNA understanding:https://www.keysight.com/upload/cmc_upload/All/BTB_Network_2005-1.pdfhttp://download.ni.com/evaluation/rf/Introduction_to_Network_Analyzer_Measurements.pdf