VNA advice - Page 1
Forum section: electronics / testgear

author: eurofox
author_rank: Unknown
timestamp: October 21, 2014, 06:14:48 pm
content: I would like to get advice from VNA users since I'm interested to buy one, I have never use a VNA before.1/ It is an expensive instrument for hobby use2/ I'm not an RF dudejust like to play with ultra fast pulses, cables, connectors, spliters .... are RF grade and would like to measure components as well with respect frequency reflection .....3/ Option 1: an old heavy second hand HP, more than 20 kg on my shelf and bulkyand 25-30 years old and still expensive4/ Option 2: an USB VNA, many options from 500 Euros to 20.000 Euros ...., I can forget the last one (http://www.coppermountaintech.com/)5/ I have a Rigol 815 + TG that I use mainly with the TG to measure cables, filters, spliters but is limited in bandwidth, I suppose that I can use a VNA to do this job as well, this way I could use the money from selling the Rigol to invest in a VNA6/ I read positive and negative feed back fromhttp://sdr-kits.net/VNWA3_Description.html,I know there are some users on the forum, input from them is very welcome. What I dislike is the limit of 1,3Ghz ... I know for the price7/ There are many other USB version but more dedicated to HAM users8/ I just came across this link todayhttp://www.megiq.com/not cheap as well but ...., any experience with this one?Thanks in advance

author: XFDDesign
author_rank: Frequent Contributor
timestamp: October 21, 2014, 06:43:39 pm
content: I have to ask, if you've never used a VNA, how do you know you need one? Practically speaking, the VNA is mainly useful for collecting small-signal like scattering parameters; nothing like pulses and such which might be better off with a TDR Scope.Can you clarify what it is you're wanting to do specifically? Your wants are all over the place. If your SpecAn w/TG isn't sufficient for higher freq bandwidths, you could always upmix an then down mix with a fixed-frequency LO and some mixers. This would certainly be cheaper and easier than a full-on VNA route.How often do you find yourself caring about return losses, matching, discrete device stability, etc?

author: eurofox
author_rank: Unknown
timestamp: October 21, 2014, 06:53:41 pm
content: Quote from: XFDDesign on October 21, 2014, 06:43:39 pmI read a lot about VNA's and the use of it and possibility to use it for components analysis, I already build power spliters and could find out my basic mistakes with the SA + TG.With respect to pulse I have a sampling scope but you can only measure the results of the design.

author: G0HZU
author_rank: Super Contributor
timestamp: October 21, 2014, 07:06:34 pm
content: QuoteYes, that's the main reason I have a big old HP VNA here. I use it to create 1 or 2 (or n) port (small signal) s parameter models that can be exported via GPIB direct to an RF simulator on a PC. Usually I design something on an EM simulator and then mill a PCB and then test it on the VNA. This is often research stuff eg recently I've been doing lots of research into microwave filters or oscillators or couplers based on defective ground structures.The modern low cost (and very small!) alternatives based on DDS technology seem to offer excellent performance up to VHF but by UHF the performance declines markedly on the ones I've looked at. So they aren't really suitable for me because most of my work is in the GHz region and I need to generate models with fairly high precision.My advice to anyone is to only buy something like a big old HP VNA if you really need to maintain high performance up into the GHz region. For many people the modern DDS alternatives will be fine and they only take up a small amount of space.

author: Howardlong
author_rank: Super Contributor
timestamp: October 21, 2014, 10:37:21 pm
content: I've had an HP 8753A for about ten years. It gets used sporadically, and I've had to repair it twice, the screen is reknowned for being a bit touchy. I also have an Anritsu S331A which is basically a one port S11 VNA which is more convenient to set up if all I need is a one port measurement.Remember you'll need a calibration kit for your VNA, they can be expensive too.For most of the HPs you'll need either an S Parameter test set or a T/R test set, you'll have an expensive papaer weight with out one. A few HPs, like the 8714, have a built in T/R test set. T/R test sets are cheaper than S parameter test sets, but you can do everything you need with a T/R test set except you'll need to turn the DUT around manually to do all the tests, although most of the time I'm only interested in S11 and S21. I use a T/R test set, in fact it's a 75 ohm one, designed for CATV, so I use a minimum loss pad to convert it to 50 ohm at the expense of a few dB of sensitivity.If you do a lot of antenna stuff, phasing harnesses and RF amps they're great bits of kit to have. I was doing an awful lot of antenna stuff when I bought mine, and it was very worthwhile for that. I haven't used the new PC based units so I can't comment on them.

author: Co6aka
author_rank: Unknown
timestamp: October 21, 2014, 11:22:26 pm
content: Quote from: eurofox on October 21, 2014, 06:14:48 pmI have one and recently used it to construct a three channel star combiner on 450 MHz; loss in the star cable worked out to be under 0.25dB, impedance on all ports was within +/- 2 Ohms of 50 nominal, with similarly-minimal reactances. Paid for itself on that one job. For what it is, it's pretty slick. The design is dated, but I imagine DG8SAQ is playing with newer DDS chipsets and ADCs by now. (And FWIW, there's a post somewhere on the 'net by a guy who re-routed the VNWA's audio out to his high end soundcard with interesting-looking results.)

author: XFDDesign
author_rank: Frequent Contributor
timestamp: October 22, 2014, 02:49:30 am
content: Quote from: eurofox on October 21, 2014, 06:53:41 pmI'm still not seeing a compelling reason to justify theneedfor a very expensive piece of test gear. Again, you're not going to get Pulse response information off of a VNA, pulse measurement specifically will be done with a Communications Sampling Scope, not any old "Oscilloscope" but a ridiculous piece of kit (http://www.tek.com/datasheet/csa8000b). Pulses are a "time-domain" kind of thing. VNAs are, in a terrible simplification, a highly glorified multi-channel Spec-An with phase measurement; a frequency domain device.Let me use the following as a metric:Q. Why is a return-loss bridge insufficient for your needs?

author: edavid
author_rank: Super Contributor
timestamp: October 22, 2014, 02:57:06 am
content: Quote from: XFDDesign on October 22, 2014, 02:49:30 amOf course you can get time domain information from a VNA!http://cp.literature.agilent.com/litweb/pdf/5989-5723EN.pdf

author: Bud
author_rank: Super Contributor
timestamp: October 22, 2014, 03:15:19 am
content: Moreover, professional VNAs use in time domain so called gating feature to de-embed parts of the circuit. For instance, in a circuit consisting of a RF connector, piece of transmission line and a actual device being tested, gating can be set to remove influence of the connector and transmission line and leave only parameters of the device.While it can also measure distance to fault, transmission line length, mismatch, etc, it is still not a right tool to measure timing characteristics though.But to the original poster's question, I'd say you could start with a inexpensive USB VNA. May be your interest will fade out and then you will not feel bad for spending $K for a industrial VNA that you not using.

author: XFDDesign
author_rank: Frequent Contributor
timestamp: October 22, 2014, 04:02:12 pm
content: Quote from: edavid on October 22, 2014, 02:57:06 amWell now, "Today I learned..."I still wouldn't use a VNA to perform that kind of measurement. It's like a Frankenstein's monster of mess to pull it off, like a poor grade FFT from a scope to do spectral analysis.

author: edavid
author_rank: Super Contributor
timestamp: October 22, 2014, 04:05:25 pm
content: Quote from: XFDDesign on October 22, 2014, 04:02:12 pmWhen you learn about TDNA your head will explode

author: eurofox
author_rank: Unknown
timestamp: October 22, 2014, 04:08:56 pm
content: Quote from: XFDDesign on October 22, 2014, 02:49:30 amThe meaning to use a VNA in this pulse measures is not directly related to the pulses itself but to the components used to design, connect .... itBelow my latest test on my sampling scope but would like to improve it.

author: KJDS
author_rank: Super Contributor
timestamp: October 22, 2014, 05:27:20 pm
content: The key to VNA performance is the directivity in the couplers and the source and load match. Some of the affects of these can be calibrated out. I've no idea where the USB tools are, but I do know that I'm happy with my HP8753C with 6GHz option.I've spent many years in the past tweaking performance of components using time domain on an 8720 20GHz analyzer. For improving component performance then using time domain then 6GHz just never gave me enough resolution to isolate things.Whether it is worth it is down to you, but I wouldn't be without mine.

author: Mr Simpleton
author_rank: Unknown
timestamp: October 22, 2014, 08:31:10 pm
content: Just to make it clear, any VNA is only as good as your calibration kit and cables.... these can cost more than just your VNA, especially if you are doing stuff over 3GHz.You say you are not an RF-guy still find 1.3GHz limiting...BTW the MegIQ starts at 400 MHz, not good in my book!I have access to a 8753E, and it is an amazing machine, still big, bulky and expensive. At home I use my NVNA v2 and I am more than happy! This is an excellent tool. Now if you do need higher dynamic range and precision why not build the N2PK variant, you can get blank PCB's and start solderingThis one goes only up to 70 MHz but offers dynamic range that equals or better the HP!BTW the 8753A have an infamous CRT that more than often fails. HP did trade in our A for an E, as they really wanted the A to disappear, and not show up as 2:d hand, I kept the s-parameter test set but this did not affect the trade-inNow what to do with that box??

author: thewyliestcoyote
author_rank: Regular Contributor
timestamp: October 22, 2014, 11:08:54 pm
content: QuoteSo true, but it does depend on what type of measurements you are doing. I my day job mostly everything is free space measurements like in a chamber. There a calibration can be nothing more than isolation and response (Admittance tunnel). This can be done with just a placement of a metal plate.QuoteThat is not exactly true, pulse response can be calculated from VNA measurement, its just a matter of some fourier mathematics. There is a python module that maybe of some interest to you called scikit-rf. It can do time domain gating, time domain transform and so on. At The heart of what's going on is a IFFT for time domain transform, and a IFFT, vector multiply with a windowing function, and a FFT to return to the frequency domain.eurofox what is it you would to measure? frequency? accuracy and precision? It can make a BIG difference in the price of the instrument. Maybe a 2 channel software defined radio could meet your needs if they are simple.

author: Howardlong
author_rank: Super Contributor
timestamp: October 22, 2014, 11:31:41 pm
content: I'm not quite sure how I forgot this, but aside from the antenna work I did about a decade ago, I also use the 8753A extensively with my crusty T/R test set to design and test dozens and dozens of RF filter prototypes, both lumped and SAW. When matching SAW filters in particular, it's difficult to think of a better tool to use: they are notoriously picky to minor aberrations from optimum matching impedances, and the manufacturers' specs on SAW filter matching are routinely complete bolleaux.

author: eurofox
author_rank: Unknown
timestamp: October 22, 2014, 11:34:51 pm
content: eurofox what is it you would to measure? frequency? accuracy and precision? It can make a BIG difference in the price of the instrument. Maybe a 2 channel software defined radio could meet your needs if they are simple.My target is to get a pulse with a rising edge as fast as possible and amplitude the highest possible.

author: G0HZU
author_rank: Super Contributor
timestamp: October 22, 2014, 11:40:48 pm
content: QuoteYes, one neat approach with many filter types is to take a raw 2 port model of the (non 50R) bandpass filter using the VNA (i.e. with direct 50R connections to the BPF) and then export the 2 port model to a computer to then model/optimise the required matching network on a simulator.I find that this is the most powerful approach specially if you want to model and optimise the matching network across the whole passband of the BPF to get the best match and/or lowest ripple on the simulator.That way you usually only have to build the matching network once and then test it with the VNA once built. You can also use the (accurate) models for the BPF and the matching network in an overall system simulator if required.

author: Howardlong
author_rank: Super Contributor
timestamp: October 23, 2014, 12:35:49 am
content: Quote from: G0HZU on October 22, 2014, 11:40:48 pmAh, but arealengineer would use a Smith chart, apparently. :-)

author: thewyliestcoyote
author_rank: Regular Contributor
timestamp: October 23, 2014, 01:43:07 am
content: QuoteA couple of assumptions about what you are testing, strictly linear(can be a big if for LNA's PA's and such). This is a function of the maximum frequency of the VNA is going to be about equal to the BW TDR or scope being used to measure the pulse. Resolution of the pulse can be much greater for VNA derived pulse response then TDR. If you increase the number of sample points it is equivalent to upping the sample rate of the TDR or scope, more detail! But the part of highest possible amplitude I am not sure why? unless you are looking for distortion vs. voltage of pulse or something like that. To my knowledge this can not be done on a VNA using, maybe there is a way but never used it.QuoteHahahaha I think I have never used the smith chart for anything other then education and talking point in presentations. Solving real world problems(not single frequency or amplitude) is almost impossible and best done by just using the measurement values in complex number form.

author: Howardlong
author_rank: Super Contributor
timestamp: October 23, 2014, 05:46:06 am
content: QuoteTo be fair, this is the best analysis I've seen of the scenario, and there's more than a fair bit of Smith chart goodness going on:http://pdfserv.maximintegrated.com/en/an/AN742.pdfIt's one of those "break glass in case of fire" application notes that needs to be kept safe somewhere for when you just might need it.All of which brings us back to the question of whether the OP needs a VNA or not. As a generalisation, and I welcome others' opinions, I'd say if you can't read a Smith chart, then a VNA is probably not what you need, and a scalar network analyser would be a more cost effective solution, or, indeed, for-two port thru measurements, a spectrum analyser with tracking generator would be just fine.This treatise may help,the OP:http://cp.literature.agilent.com/litweb/pdf/5965-7917E.pdf

author: thewyliestcoyote
author_rank: Regular Contributor
timestamp: October 23, 2014, 06:20:34 am
content: QuoteSCFTW! wow nice thanks for the link! It is a great tool to get a idea of what is happening. It also show the 4 types of passive devices resistors, capacitors, conductors, and transition lines and there relationship. I am not counting mem-resistor because you I can go to mouser, digikey, or where ever and order one. They show the equations! and when design something that is what you need.QuoteI had a talk with the professor I will be getting my masters under and the best ideas in 10 mins for measuring these kind of devices with a signal source and 2 channel vector signal analyzer. To same thing about math of S-parameters of these kind of devices are Fourier coefficients or transform not just a complex value for each of the parameters. This is a very complex type of measurements. So if you can stick to "linear devices" and work in the small signal range of LNA's, PA's and other non linear devices.

author: G0HZU
author_rank: Super Contributor
timestamp: October 23, 2014, 03:44:01 pm
content: Quote from: Howardlong on October 23, 2014, 12:35:49 amI still use a PC based smith chart matching program for simple narrowband matching tasks but for wideband low loss circuits the most efficient way to do it is by taking an accurate 2 port model of the filter (or coupler or RF switch etc) from the VNA and doing it all on a simulator. This way you can analyse and optimise the matching across hundreds of frequency points in real time and the computer takes into account S11 S21 S12 and S22.I've even used this approach when matching narrowband stuff like a high impedance crystal filter. i.e. measure it unmatched with direct connections to the 50 ohm VNA and then export a 2 port model (S11 S12 S21 S22) to a simulator and then design/optimise a match circuit (to 50 ohm) for this model on a simulator.The oldschool smith chart method is OK for narrowband matching to known/fixed impedances but it's not as powerful as the above method. You also get the bonus of getting accurate n port models to use in a system simulator.

author: KJDS
author_rank: Super Contributor
timestamp: October 23, 2014, 04:30:52 pm
content: I still use a smith chart when matching in microwave office or ADS. It makes it easier to see what's happening as you build up a matching circuit whether it's broad or narrow band. I can't imagine trying to match to the input of an RF power transistor, where the input impedance may be 0.5ohms with a chunk of series inductance without the aid of a smith chart.

author: PA4TIM
author_rank: Super Contributor
timestamp: October 23, 2014, 05:17:28 pm
content: F@$#g Windows explorerSpend an hour typing, typed a few backspace and the browser leaves this page and away is my text. This was the last time, Now I'm sure, I will replace it by Linux on this laptop too.http://www.pa4tim.nl/?p=1594I made a series of tutorials because there was/is not much literature aboutt NA for beginners. I had to learn it by myself the hard way.I have 2 VNWA's, 2 HP-8407 and a lot of accessoires.Calkits are the most important together with cables. My best cables are 279 euro a piece (I got them for free from a friend), besides that mil grade RG58 (the see through version), home made extra shielded belden/radial cables for bnc and GR cables.I use calkits from Amphenol, rosenberger (sma), homemade (N and bnc) and from GR (GR874 and GR900)You need fixtures and adapters too. All those things can be much more expensive.The results depent very much on the way you measure and calibrate. You can not make good measurements with a bad calkit.My interest in VNA's is component behaviour related.I like the VNWA a lot, it has a lot of functions. OK, it is limmited to 1500 MHz (only with my best cables and call kit) but if you want to play at 6 GHz the calkit you need for that will cost a lot more as a complete VNWA.

author: G0HZU
author_rank: Super Contributor
timestamp: October 23, 2014, 05:51:45 pm
content: Playing about with a smith chart can only take you so far.The main function of a modern n port VNA is to extract n port model data from it and then to make best use of this data (usually in a simulator).If you just use it to look at S11 and then decide to go off and play with a smith chart and a pencil (as in classic impedance matching tutorials as found in books like Bowick) then you aren't making best use of the instrument's full potential or the potential of modern RF simulation packages.It's 2014 not 1965

author: eurofox
author_rank: Unknown
timestamp: October 23, 2014, 06:16:03 pm
content: Quote from: PA4TIM on October 23, 2014, 05:17:28 pmUse Chrome, is not perfect but better.QuoteI already download all of themThanksQuoteI have already very good cables with the ultra fast pulses it is mandatory, today I scored 27ps rising edge.QuoteI have the same interest with respect to component testing, I'm not an RF guy but I do have an RF generator, a microwave generator that I build myself, a Rigol 815 + TG and a 21Ghz HP SAQuoteHow did you manage to get 1,5Ghz since it is supposed to be limited at 1,3Ghz?

author: G0HZU
author_rank: Super Contributor
timestamp: October 23, 2014, 06:22:24 pm
content: Quote from: KJDS on October 23, 2014, 04:30:52 pmYes but you ARE using a simulatorIf we stick to looking at small signal (linear) analysis then the crude oldschool way would be to just measure the S11 (and S22) of the whole circuit with a VNA and then go off and try matching to it using a smith chart and a pencil. This would run into problems if matching changes to the output side of the network affected the input S11. So at best this would require an iterative approach with lots of soldering/desoldering of components and lots of VNA time.

author: KJDS
author_rank: Super Contributor
timestamp: October 23, 2014, 06:51:27 pm
content: Quote from: G0HZU on October 23, 2014, 06:22:24 pmI agree, I can't remember that last time I used a paper smith chart. I just like looking at one in MWO or ADS as I'm sorting out the matching.My typical approach for an LNA, where we can think only about the small signal case, is to start with the device s-pars and add some source inductance to improve the stability. Then I'll start working the match outwards, first with the output match and use that to push the optimum noise figure point towards the input impedance. Depending on frequency I'll either use lumped or distributed components. If I'm using lumped then I'll also add in some microstrip lines into the models between the components for anything above VHF. I'll then work the input and output matching circuits until I'm happy. Sometimes I'll leave the optimizer to run if I'm fairly close, however it's always worthwhile checking just what the optimizer is doing. Nothing worse than getting great performance after optimizing only to find out it's put in something impractical.Too often I've seen engineers run the optimizer, build the circuit and miss something fundamental, like a tuning cap sitting in series with a bias line. The S parameters will still say that it will work.I started out in the 80's when VNA time was hard to come by, much hair pulling and too many iterations. A lot of time on the bench chasing issues that today you'd sort out before the layout started. I have no idea how people managed PA design then, except that mostly what they did wasn't that good.

author: Howardlong
author_rank: Super Contributor
timestamp: October 23, 2014, 06:59:51 pm
content: Quote from: G0HZU on October 23, 2014, 06:22:24 pmBeen there, done that. It's worth it for the learning experience, I found it very educational. At the end of the day, we all need to get the hot pointy thing out anyway!

author: KJDS
author_rank: Super Contributor
timestamp: October 23, 2014, 08:43:37 pm
content: Quote from: Howardlong on October 23, 2014, 06:59:51 pmThe last discrete LNA I did was very very close without the soldering iron. If the model is that close, then tweak the model a little to give the change you want, then get the soldering iron out. It's far far quicker to try five different variations in MWO or ADS than it is with a soldering iron, especially when you're working with 0201 or smaller.

author: Howardlong
author_rank: Super Contributor
timestamp: October 23, 2014, 09:33:12 pm
content: My standard for production boards for the past four years has been 0402, I can at least reasonably hand solder them under the microscope, or if I'm doing several boards in a panel of ten or so, I can hand place them on pasted boards for reflow with just an illuminated magnifier which speeds things up. You can reasonably squeeze a track between on 0402, not sure you can get away with that on an 0201. 0201 is a rarity for me, I've only used them twice, and it has to be under a microscope. My board assembler only recently acquired a pick and place machine good enough for 0201: they tell me it'll go to 01005, I know I won't be doing that soon.

author: thewyliestcoyote
author_rank: Regular Contributor
timestamp: October 23, 2014, 10:12:07 pm
content: Haha discrete components, its all about the minimum number of components and doing everything in physical structure of the board, material so on, that is the real design magic is. Say hello to HFSS, FDTD, FEM, or MoM. Ok joking aside. For simple the using the smith chart is great because of the learning experience of it. But it all comes down to what you are doing, if you are making a lot of measurements or specialised measurements there is no way around it VNA's and good software. If you are a little computer savvy you can save your self thousands of dollars in software, hardware, and the kind of stupid software options for it. Again I don't know what is your frequency range but a Keysight fieldfox is hard to beat, they can function as 2 port VNA and spectrum analyzer with signal generator. If you need more ports then 2 then invest in a good switching network. Have a play with python and scikit-rf. I wrote some python to control fieldfoxes, I will try and find it and post it. I am a bit biased to Agilent/Keysight.

author: G0HZU
author_rank: Super Contributor
timestamp: October 23, 2014, 11:49:10 pm
content: QuoteIs this called pulsenutting?Not sure how a basic low cost USB VNA is going to prove very useful to you if you are already trying for that level of performance?

author: thewyliestcoyote
author_rank: Regular Contributor
timestamp: October 24, 2014, 12:24:01 am
content: QuoteThe only way to get smaller and smaller equivalent requirements is to measure higher and higher frequencies and good phase resolution. There are ways to get equivalent response by generating a approximate circuit (LRC and transmission lines). This can be a dangerous game to play as it extrapolation not interpolation. None of these are direct measurement of pulse response, but given some basic assumptions(trap for young players as Dave would say) like linearity and complexity or circuit. I do not know the measurement performance of the USB VNA in question.

author: eurofox
author_rank: Unknown
timestamp: October 24, 2014, 03:27:55 pm
content: For people who want learn the smithchart.http://www.fourier-series.com/rf-concepts/smithchart.html

author: thewyliestcoyote
author_rank: Regular Contributor
timestamp: October 25, 2014, 06:10:53 am
content: QuoteThere was a couple of YouTube videos that really helped me when I was just learning about the smith chart in school.

author: barnacle2k
author_rank: Regular Contributor
timestamp: October 29, 2014, 06:13:38 pm
content: Since we have a nice VNA thread going here:I have the opportunity to buy a E-CAL module (With USB and Parallel port) for my 8753E.But i would need a 85097 interface module to connect it to my VNA, now i wondered if anyone ever tried to build one.It seem to be only a power injector / level shifter as of this:http://www.keysight.com/owc_discussions/message.jspa?messageID=54151#54151Or is there software to control it from a normal PC over USB?

author: cncjerry
author_rank: Unknown
timestamp: October 29, 2014, 07:26:11 pm
content: I bought one of those boards asian boards, I think it is generically called a winnwt? or a nwt500? It does a decent job for the money from 0-500Mhz. It can also be used as a simple SA as well as a DDS signal source. Gives impedance with phase, has some built in attenuators, etc. The RLB that came with it works ok though I built my own directional couplers using Minicircuits transformers that seem to work better. The NWT500, just search on ebay, only runs like $175 but it maps perfectly against my SA with TG.If you just want scalar output, all you need is a noise source and a scope with FFT and long persistence. That will give you a curve but you have to work to get impedance and no phase.I am also playing around with the ADL5519 from Analog devices. A pair of them with I/Q signal source will give you forward/reflected as well as phase though I haven't worked out the phase part. Those chips aren't cheap, but with a 20db directional coupler you can also use it as a fairly accurate power meter across 60db or so without switching. The app note and data sheet have good examples.So if you had a pair of the ADL5519 for like $9 per = 18, plus an I/Q DDS for $50 plus two DCs with connectors at $20 per, etc and a microprocessor, you would throw together a simple VNA with power measurement for under $200. I haven't done it yet, but plan to and I will add external ADC 16 bit or more to get higher resolution than the typical micro at 12bit with averaging.I've been looking at VNAs and commercial high-function products are very expensive. But using the NWT500 coupled with a computer should give you just about everything you would want. You would have to write software to do in channel power measurement and other things my spectrum analyzer does but hey, it's a project.Jerry

author: Marco
author_rank: Super Contributor
timestamp: October 29, 2014, 11:13:09 pm
content: The Chinese "clone" uses the software for the original NWT-500, but the hardware is very different (and the firmware is slightly buggy and closed source). So yeah, it might work ... but it's very shifty.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 30, 2014, 12:01:37 am
content: Quote from: edavid on October 22, 2014, 02:57:06 amInteresting article--HP had a tutorial back in the early '90s describing this,They don't teach young EEs much history,though!---"Then, in the 70’s, it was shown that the relationship between the frequency domain and the time domain could be described using the Fourier Transform"1970s, my bum!!

author: XFDDesign
author_rank: Frequent Contributor
timestamp: October 30, 2014, 12:41:32 am
content: Quote from: vk6zgo on October 30, 2014, 12:01:37 amI got plenty of theory (re FFTs), but in this case we have the guy who is trying to use a hammer for things that are not nails. I can also apply the FFT route on my scope to get a pseudo Spec-an, but that doesn't mean it does the jobwell. Unlike a spec-an, the VNA gets phase information too, so sure, you can back-interpolate, but that doesn't mean the end result isgood. It's one of my beefs with test gear today: little is made where it's primary purpose is done well, but instead it's made to do too many things and does them poorly.

author: tggzzz
author_rank: Super Contributor
timestamp: October 30, 2014, 01:51:56 am
content: Quote from: XFDDesign on October 30, 2014, 12:41:32 amIt is one of my beefs with many things nowadays - too many "marketing festures" and tick boxes.

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: October 30, 2014, 07:16:49 am
content: Quote from: Mr Simpleton on October 22, 2014, 08:31:10 pmYou can buy color LCD kit for it on Ebay.

author: KJDS
author_rank: Super Contributor
timestamp: October 30, 2014, 07:32:10 am
content: Quote from: XFDDesign on October 30, 2014, 12:41:32 amUsing time domain with a VNA is a very powerful technique that many RF engineers have used to improve products. If you want a decent coupled line directional coupler then the lines alone need to be 50* ohm, and that includes everything after the lines stop running parallel, so corners and transitions to coax or a load. Being able to sort the discontinuities and measure the overall performance with the same piece of equipment is so useful when optimizing a design.

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: October 30, 2014, 08:01:38 am
content: Quote from: vk6zgo on October 30, 2014, 12:01:37 amFFT (Fast Fourier Transform) algorithm was popularized in 1965 according to Wikipedia. I believe that application of FFT became feasible in around 1970 when algorithm and computing power were at levels when such application became practical. I don't think they were referring to Fourier transform itself.

author: tggzzz
author_rank: Super Contributor
timestamp: October 30, 2014, 09:44:15 am
content: Quote from: Alexei.Polkhanov on October 30, 2014, 08:01:38 amYes, but the modern form of theFourier Transformwas first stated150 years earlier, in 1820.Hells teeth, I was introduced to Fourier Transformsin school(not university) in the early 1970s!Youngsters indeed.

author: XFDDesign
author_rank: Frequent Contributor
timestamp: October 30, 2014, 05:31:02 pm
content: Quote from: KJDS on October 30, 2014, 07:32:10 amOk, and what's the sticker price on the VNA you use to do this with? Here at work, we just dropped $500,000 on an Anritsu 70GHz VNA which does almost everything under the sun (including a few methods of measuring NF). I suppose I could suggest such a beast to the OP.

author: eurofox
author_rank: Unknown
timestamp: October 30, 2014, 06:45:01 pm
content: QuoteI will give you my address and you will be very kind to ship it to me

author: XFDDesign
author_rank: Frequent Contributor
timestamp: October 30, 2014, 08:05:54 pm
content: Sure, if you can provide a $600,000 payment.

author: TerraHertz
author_rank: Super Contributor
timestamp: October 31, 2014, 01:39:35 am
content: Quote from: XFDDesign on October 22, 2014, 02:49:30 amGiven that decent old VNAs seem to be available in the 1 to 3 thousand $ range, isn't simply wanting to learn the techniques, using professional test gear, reason enough? Working applications come later. Also some of us simply don't care about 'return on capital' since our objectives are not economically motivated.I don't have a VNA, and know I don't yet know enough to usefully apply one. However a decent VNA and associated S/T-R and cal sets is on my 'eventually' list. In the meantime I'm still trying to learn RF basics. This thread has been an interesting read, with lots of useful references. Thanks.Incidentally, for Smith chart historical reference there's this 1969 book "Electronic Applications of the Smith Chart" by the developer of the chart, Phillip H. Smith. Pic at ebay 231328916531.Several posters have very briefly referred to network analysis software they use. For those of us with no working experience in this field, could people familiar with such utilities please post some details? Like package names, sources, freeware/cost, and comments on the intended purpose and quality of the software?Notes like "It's a pain in the butt because it doesn't do ...." can save an awful lot of time for beginners.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 31, 2014, 02:27:45 am
content: Quote from: Alexei.Polkhanov on October 30, 2014, 08:01:38 amBut that is not what they said-----if they meant solving Fourier Transforms with a computer,they should have said just that!Stuff published by Agilent/Keysight has become increasingly lightweight over the years,with Marketing taking precedence over Engineering.

author: Howardlong
author_rank: Super Contributor
timestamp: October 31, 2014, 05:20:14 am
content: Quote from: Alexei.Polkhanov on October 30, 2014, 07:16:49 amYip, I already ordered one a few days ago as this thread prompted me to do something about mine. Considering it's 30 years old, it's astonishing that the market value of these things continues to be maintained, goes to show what good engineering is all about, except for that pesky CRT that is!

author: KJDS
author_rank: Super Contributor
timestamp: October 31, 2014, 08:09:38 am
content: Quote from: TerraHertz on October 31, 2014, 01:39:35 amI've started a new topic rather than further derail this one.https://www.eevblog.com/forum/testgear/rf-design-software-a-follow-up-from-vna-advice/

author: coppice
author_rank: Super Contributor
timestamp: October 31, 2014, 08:26:42 am
content: Quote from: vk6zgo on October 30, 2014, 12:01:37 amWhere is that quote come from? I think the timing is a little off. From memory I think it was the 1790s rather than the 1770s. Laplace was active in the 1770s, but Fourier was a bit younger.

author: coppice
author_rank: Super Contributor
timestamp: October 31, 2014, 08:38:43 am
content: Quote from: Alexei.Polkhanov on October 30, 2014, 08:01:38 amThe quote is about the Fourier transform, not the FFT. Fourier transforms can be performed in several ways in practical engineering systems. Before it was practical to build an FFT in software or digital hardware a lot of systems used optical Fourier transforms. Some advanced radar systems were doing this in the 60s. Fourier transforms in optics are still a big deal.As someone else commented, it appears Gauss was the first to formulate the FFT, but it was forgotten and rediscovered multiple times. Without automated ways of calculating a numerical Fourier transform there wasn't a lot of interest in them until the 1950s, when computers first became available, and people started performing DFTs in software. The slowness of the DFT made people search for shortcuts. Cooley and Tukey rediscovered the FFT thinking there were the first, but it soon became obvious they were not.A lot of stuff gets lost if people don't use it. LDPC was first described in the early 60s, before digital comms took off. We went through years of poorer coding schemes before that one was rediscovered.

author: XFDDesign
author_rank: Frequent Contributor
timestamp: October 31, 2014, 03:53:10 pm
content: Quote from: TerraHertz on October 31, 2014, 01:39:35 amI don't think there is a particularly right or wrong answer to this question, because it is a philosophical one.In my opinion, just buying a piece of gear every time you want to "learn" something is something of a lie. One isn't wanting to learn something, but pay for what others have learned as a kind of short-cut. Consider, what piece of test gear do those who are learning (i.e. researching) in the domain of 220GHz+? Repeat this kind of thought experiment rolling back to the developments in Radar in WW2. In essence, it really isn't learning, but "buying" your way to knowledge without a lot of the core supports. You can see this with a lot of spaghetti-against-the-wall spice designs, where people have the tool that "tells" them whether something works or it doesn't. They then throw parts at spice until it spits out a desirable answer - one which might not actually work in the real world.When I read the comments in this thread, almost everyone has the fundamentals. They "get it" and are using the tool as an expression of those fundamentals. It's how some people say they don't bother with the smith chart, or leverage some tools in particular ways - each have their methods of using the basics to get to their end result. If their instrument is giving them a bogus result, they have a reasonable expectation of what theyshouldbe getting instead of what they are. Someone who just picks up a VNA, turns it on and starts "collecting data" to "learn" with, doesn't have that.

author: eurofox
author_rank: Unknown
timestamp: October 31, 2014, 08:09:37 pm
content: Quote from: XFDDesign on October 31, 2014, 03:53:10 pmDisagree with you, I spend my career mainly in automation, electronic and mechanics as an engineer but most of the time in middle management and executive management having a bunch of engineer working for me. I speak 7 foreign languages and was active in many country's.I'm retired now and was never involved in RF, you are telling me that I have to go back to school or read 200 book about RF technologyI have NO INTEREST in RF in general, I don't care about RF amplifier and antennas, I'm interested in ultra fast rising pulses and therefore to improve my design need to understand some aspect of RF technology, that is the only reason why I'm interested in a VNA to improve my cables, connectors, splitters ...I'm able to design pulses with rising edges below 30ps, you can compute the RF frequency for this yourself.

author: G0HZU
author_rank: Super Contributor
timestamp: October 31, 2014, 09:26:29 pm
content: Have you considered spending some time with an RF simulator?The good ones can mimic an 'n port' VNA and you could mess about with simulated splitter designs and transmission lines up into the GHz region and you can also model the circuit in the time domain on the very best simulators. eg you can inject simulated pulses of your own spec to the simulated circuit. This could prove a useful learning curve and it may help you choose the spec of your 'real' VNAFor example: It's very easy to make a precision wideband resistive splitter up into the GHz region if you follow a few basic RF design rules. The last one I did, I designed on a simulator (Genesys + Sonnet EM) and the measured results were pretty much bang on with the simulator up to several GHz. So it was arguable that the 'real' VNA wasn't needed. However, if I wanted to make a splitter that worked well up beyond 10GHz then I would need to use a real VNA to verify my various component models. But up to 6GHz, say, its fairly easy to produce a decent model of a tiny SMD resistor and a decent RF simulator and a decent RF layout can do the rest.I still think you will find out that you will need a very fast VNA for your project. But if this is the case you will also need some very expensive test fixtures and cal kits and a fair bit of RF experience to get the best from it and to avoid falling into a few traps. However, you could probably learn enough to get good results with just a few days' decent study time, especially if you can find an experienced tutor to sit with you as well

author: XFDDesign
author_rank: Frequent Contributor
timestamp: November 01, 2014, 02:21:35 am
content: Quote from: eurofox on October 31, 2014, 08:09:37 pmIt's perfectly find to disagree with me. Your long list of achievements are commendable (I can barely do 4 languages), but not really important or relevant to this particular topic at hand though. There was a guy at Tektronix, an MIT graduate who wastheexpert in superconducting something or other. Ask this guy anything about superconductors, inside or out, and he could give you answers. One day, this guy frantically waffled around to all of the surrounding labs, and told everyone to shut down, because their labs emitted too much noise for his sensitive measurements. So everyone complied, albeit grudgingly. The guy never came back, so after a while everyone went back up. A bit later, he comes back and barks the same orders. Finally someone decided to go see what the hell it was he was trying to do. The guy went on, in great detail about his experiment, but in the end, what was it that originated all of the commotion? He was trying to measure a 4GHz signal, of anticipated 500uV amplitude.On a 200MHz scope.On 50mV/division with full power bandwidth.There are many disciplines, and being a master of one does not automatically make one a master of all others.If your purpose is to buy a VNA, for the sake of it, go for it. Apparently you'll need one that's capable of doing the inversion back to time domain, and even still if you're on that blisteringly fast edge of speed (supposing 30ps rise time), a cheap 3GHz VNA is unlikely to be a benefit.

author: ivaylo
author_rank: Frequent Contributor
timestamp: November 01, 2014, 06:18:54 am
content: QuotePeople learn differently, man... If you tell me one way of learning is better than another, I'll have to disagree too. Call me an idiot, but I remember for the first time I got what a current source was when I laid my hands on a PSU with a CC mode. Yet on paper I cuold solve the craziest circuit with Kirchoff, Thevenin and what not...

author: eurofox
author_rank: Unknown
timestamp: November 01, 2014, 08:49:28 am
content: Quote from: ivaylo on November 01, 2014, 06:18:54 am+1

author: XFDDesign
author_rank: Frequent Contributor
timestamp: November 01, 2014, 11:51:46 am
content: Quote from: ivaylo on November 01, 2014, 06:18:54 amQuote from: XFDDesign on October 31, 2014, 03:53:10 pmLearning itself, is an integration of concepts. You had the math to "solve" a few styles of problems. You had a piece of gear which took the practical component and combined it with the math component, and then you "got it." You learned the concept of a current source and could then have that tool in your tool box.What would that experience have been like, without the basics of understanding KCL and KVL? What if you only had a power supply that had both CV and CC mode, but none of the fundamentals behind it?

author: eurofox
author_rank: Unknown
timestamp: November 01, 2014, 04:19:33 pm
content: QuoteIf you think you have the exclusivity to have "maybe" the knowledge of RF technology you are really an idiot.This forum aim is to share experience an not to waste time arguing with pretentious people.I learn what I want the way I want and your comments here are simply ridiculous, most people here try to help but obviously you are an idiot thinking that you are smarter than others.

author: XFDDesign
author_rank: Frequent Contributor
timestamp: November 01, 2014, 05:35:20 pm
content: Quote from: eurofox on November 01, 2014, 04:19:33 pm"When the debate is lost, slander becomes the tool of the loser."Perhaps you wish to quote me where I stated that I have an exclusive ownership of knowledge in RF? Or perhaps you wish to quote exactly where I said I am smarter than others, for surely you observed the point where I was informed about VNAs being used for TD measurements. No, what you're shopping for is not "help" but an excuse to buy something. Don't ask for advice, if you don't want to listen to what you're given. Fundamentally, you've presented no actual argument, either in calling me an idiot, or your "disagreement."Cheers.

author: eurofox
author_rank: Unknown
timestamp: November 01, 2014, 06:00:28 pm
content: Quote from: XFDDesign on November 01, 2014, 05:35:20 pmI'm retired after a full career, what I do I do it for pleasure, on this forum people are usually friendly.I have no need to get very deep into RF technology but I do have a SA up to 21Ghz, a microwave counter/counter meter, an RF generator and I build myself a microwave generator and I can use and fully understand all those instruments.I don't cry for help, just share people experience in some specific area is that all and many people kindly answer , only one was playing the smart-ass.I never touch a VNA in my life like most of EE engineers and I was just asking some advice but in the mean time I order an new VNA this way I will be able to learn without asking advice an get unpleasant reaction

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: November 01, 2014, 07:10:01 pm
content: Eurofox you live in the middle of Europe - everything is around you. When I needed VNA to debug my RF project I just went and rented one from local cal lab for $350/week. Better than buying one for $38K and not using it. Vancouver is not that big on electronics, so cal lab that used to rent equipment got new owner and they don't rent anymore. 6 pack of beer and trip to a buddy with VNA works as fineGood way to meet new people that have interesting projects is to join local hackers club and then you meet people that have something you don't and in reverse. I found that what works better than beer is an interesting project - if you have something built already like wide band antenna, microwave filter, ... or anything and then you need equipment to test/tune it almost certainly there will be people more than wiling to help you.World is an interesting place - I have seen people with $5M worth of equipment in a lab that does nothing ... errr humidity sensors, and then I see dudes that have bunch of super exciting projects like air pollution radars, 3D scanners, amateur radio telescope receivers which they finish with 30 y old analog scopes and always looking for test equipment to debug their stuff.

author: eurofox
author_rank: Unknown
timestamp: November 01, 2014, 08:39:02 pm
content: Quote from: Alexei.Polkhanov on November 01, 2014, 07:10:01 pmYou know some people spend 500 thousand Euros for a stupid super exclusive watch or 100 thousand for a special stamp, my lab is my way to keep myself busy en enjoy what I'm doing, I'm retired and have a lot of time.

author: Howardlong
author_rank: Super Contributor
timestamp: November 01, 2014, 11:04:55 pm
content: So my experience may go against the grain of some of the "professional" EEs on here.I've been fiddling with electronics since about 1973 when I made a crystal set with my old man. To be honest I think he enjoyed doing it as much as I did. I was eight years old. At eleven, I wrote my first program in Algol 60 on paper tape. At twelve, I'd designed and built a digital clock out of 74 series TTL ICs. I used to tell my mum off for using the washing machine because my clock's time base ran off the mains 50Hz, so it skipped many seconds while the washing machine relays etc clicked through. That was 20 odd ICs all hand wired, and I designed the whole thing myself. When I was 13 I built my first computer, again hand wired, based on an older school friend's design. I still have it, although I doubt it works any more. At 15, I was designing my own computers. I then did a EE degree, worked in ATE (automatic test equipment) for a while, and then sold myself to the devil and did software professionallyalmostexclusively for 25 years.Back in the 70s, having a scope was sheer luxury (Monty Python fans please note). The holy grail (oops) was a scope, and if really lucky it was dual trace, but the nerdgasm of the day was a scope with a dual trigger, not that I had much clue what to do with that at 12 unless I was tutored by my older peers. I didn't own a scope myself until I was in my mid-twenties. My debugging tools were a 1k ohm per volt analogue multimeter and an LED with a resistor. Plus, the nose to "smell" the heat, and the back of the finger to do a similar thing, both techniques I still use to this day.I am absolutely certain that having the right tools, particularly a scope, back in the day it would have speeded up debugging of problems, but you can get away with an awful lot with a crappy meter and an LED, and a good degree of healthy persistence.More recently, about 1999, I got back into RF, and was doing a lot of work on antennas at VHF and above, but particularly in the 2.4GHz band. After messing about with SWR bridges in 2000/2001 for some time I bought that 8753A VNA with a T/R test set. I'd spent some months investigating and gritting my teeth about blowing £3k on such a thing. At that time I wasn't making a living from electronics either, this was an academic pursuit. It was an eureka moment. Pretty much my understanding of impedance matching and how antennas and transmission lines work suddenly clicked into place. Yes, I knew about phase, Smith Charts, return loss etc. But I'd never had a way of applying it so directly and seeing it so interactively.Since then, I've gone on to many other things, all with RF connections, including designing and troubleshooting several items of space hardware that are orbiting the planet right now. I rarely take those old software contracts anymore. These days I get asked to universities to teach postgraduate students. I'm still astounded at how little real applied knowledge there is out there.Of course, the well-paid bean counters still think they are saving everyone a buck by offering crap wages to inexperienced workers and bugger all equipment. Yes, you can do an awful lot when you don't have the best test equipment, but it takes a lot of patience and analytical skills. That means time, and as any well-paid bean counter should know, time is money.

author: eurofox
author_rank: Unknown
timestamp: November 01, 2014, 11:44:44 pm
content: I build on the age of 13 my first oscilloscope with valves and continue to be passionate by electronics until I got graduated as an engineer and PhD.I start building my first computer in fact a PCB with ram, prom and display and HEX keyboard with I/O's on the very beginning when µprocessors became available.I wrote code in hex, when computers became available I start to use assembler.I got my first real oscilloscope when I was 23, it was an HP that I could buy second hand.I work several year in automation on many project, design during the CP/M time a SCADA system and start to develop protocols to communicate with PLC's, this was in the beginning of the 80's.Shortly after this period I moved to middle management and up to executive management. I was plant manager for many year with different divisions, the biggest one was electronics assembly with up to 300 people only in this department. I learn everything about pick-place machines and production.The last 5 year of my career I was involved in photovoltaics from physic up to participate on getting a complete production plan ready.Most of my professional live I got my lab at home and from time to time did some freelance projects. After the Apple II appear on the market I designed a compatible system with 80 column instead of 40 original from the AppleII, the guy for whom I designed never got the money to put it on the market.I still program for the fun micro controllers in C and assembly.Now I 'm retired and catch up again with electronics, I do it as a pleasure and learn new things the way i want it.

author: G0HZU
author_rank: Super Contributor
timestamp: November 01, 2014, 11:49:13 pm
content: QuoteI think you could also have done the same with a decent simulator and a decent smith chart programI would argue that you can learn more and learn it quicker with access to a decent simulator. Obviously there is a bit of a learning curve with the simulator but a modern simulator is usually the most powerful tool in the box. Usually way ahead of a VNA if you want to explore new concepts and do research work.When I started doing RF design professionally 25yrs ago we had a HP8753A T/R VNA and it was a fabulous bit of kit. But what I really wanted to have at home was the CAD software we were using. Back then it was DOS based stuff called star/sstar/pro from Circuitbuster (later to become eagleware).Today, the modern CAD tools take you to learning levels way beyond having a 'real' VNA on the bench.

author: eurofox
author_rank: Unknown
timestamp: November 01, 2014, 11:55:20 pm
content: QuoteI can agree but what is the cost of such a simulator ?What could you advice that is affordable?

author: G0HZU
author_rank: Super Contributor
timestamp: November 02, 2014, 12:00:27 am
content: It would be very expensive to buy AWR or Genesys products as a private individual. It could easily end up costing $20k or more if you want to add a few options. If you search online you will see that some hobbyists choose to hack the SW and run it for free at home. I'm not sure anyone really minds if this happens at the hobby level but it becomes much more serious if a company tries the same.RFSIM99 is quite good as freeware though. However, I don't think it would be what you need.

author: Bud
author_rank: Super Contributor
timestamp: November 02, 2014, 03:30:05 am
content: Quote from: G0HZU on November 01, 2014, 11:49:13 pmWay beyond that is true because the firmware in the bench devices is limited in its math and presentation capabilities.However, there is a magic in a real VNA on the bench. You touch it, you connect real circuits, you learn how strays, parasitics and different setup can affect real measurements.

author: TerraHertz
author_rank: Super Contributor
timestamp: November 02, 2014, 03:52:25 am
content: Quote from: XFDDesign on October 31, 2014, 03:53:10 pmActually I meant it as a rhetorical question, to illustrate a point. So you're right.QuoteWell now, that very much depends on the details. For instance, as someone with no RF experience and little theory, but a need/desire to know, I decided my best path was to start with very basic gear. So I bought some slotted lines, SWR meters, power meters, vector voltmeter, and so on. Because I'm well aware that trying to use more complicated gear before I understand the principles is a trap waiting to be sprung.QuoteI don't think your point here is very logical. Yes, some people with fundamentally broken learning abilities will take silly paths, and produce rubbish. That isn't a basis for never buying expensive equipment as a learning aid.QuoteAgreed. having some idea of what resultsshouldbe, is very important. That's why learning is a process. However there's still nothing wrong with buying test gear appropriate to one's present position on the curve. Whether economics factors are important to someone or not, is an entirely separate matter, and depends on their circumstances and objectives. Some people may make silly choices in their circumstances; that doesn't mean the same choices by other people are necessarily silly.As for using simulator software packages - in many cases buying these can cost more than 2nd hand test gear providing similar abilities. Also personally I prefer hands-on learning. Simulators have their place, but I'm not a fan of paying lots of money for software, especially since experience has taught me that compatibility lifetimes can be quite short. How many old CAD tools do I have that won't run (or just aren't installed) on my current machines? I hate to think. I'm developing a bit of a PC phobia actually.

author: Howardlong
author_rank: Super Contributor
timestamp: November 02, 2014, 05:21:14 am
content: Quote from: G0HZU on November 01, 2014, 11:49:13 pmHere are a couple of (delibrately facile!) arguments for you from my experience of simulators.I played drums in Guitar Hero, and thinking I was quite good at it, I bought a drum kit, only to discover the real thing's completely different.I also spent many years on and off on Flight Simulator, then I learned to fly for real. Sadly FS taught me an awful lot of bad habits I had to unlearn, making the real learning process that much harder.Going back to my degree-level education, I was amazed that by far most of the EEs I learned with left university without ever having picked up a soldering iron in the three years they were there, but they could derive some really obscure contrived calculus problems two or three ways. I know that between a soldering iron and calculus in real life, the soldering iron gets a lot more use.Personally speaking, I find that I learn better by doing real, practical things rather than relying on more abstract methods, altnough I accept that others may be more comfortable wih those abstract methods. I also accept that a lot of the time I will also get it wrong particularly if it's something I've not done before, which in itself is also a very valid part of the learning process.

author: Howardlong
author_rank: Super Contributor
timestamp: November 02, 2014, 05:32:33 am
content: Quote from: eurofox on November 01, 2014, 11:44:44 pmMe too, assemblers were pie in the sky. I knew the entire instruction set in hex in my head. Here's the remains of my first computer...http://www.g6lvb.com/when_i_was_a_young_chap.htmQuoteI went the other way, I knew I couldn't do management, so I've worked for myself for the past 23 years.

author: tggzzz
author_rank: Super Contributor
timestamp: November 02, 2014, 10:14:45 am
content: Quote from: Howardlong on November 02, 2014, 05:32:33 amHex keypad? 1kbyte RAM 512byte PROM? Luxury.Mine had 128bytes RAM and 16 bytes "PROM", and the keys were toggle switches destined for car dashboards.Internally it worked reliably, but, um, let's say I learned a lot.

author: Howardlong
author_rank: Super Contributor
timestamp: November 02, 2014, 10:27:47 am
content: Quote from: tggzzz on November 02, 2014, 10:14:45 amSheer luxuryhttp://youtu.be/Xe1a1wHxTyo

author: tggzzz
author_rank: Super Contributor
timestamp: November 02, 2014, 10:41:12 am
content: Quote from: Howardlong on November 02, 2014, 10:27:47 amJust so.I might or might not still have schematics for the "WeenyBitter", a homebrew computer built from TTL. I do still have the autocode instruction set (and music played on its loudspeaker) for an important commercial 39bit, 2kIPS, 8kWord computer. Must go to Bletchley Park and see it again someday.

author: G0HZU
author_rank: Super Contributor
timestamp: November 02, 2014, 12:16:39 pm
content: Quote from: Howardlong on November 02, 2014, 05:21:14 amOK, here's a very crude example of the power of a modern EM simulator.Suppose you were given the task of designing a multilayer directional coupler or multilayer filter up at a few GHz or so. eg something on a 4 layer PCB that maybe used a defected ground on an inner layer as a critical part of the design.Would you design and optimise it by hand with a VNA or would you use a simulator? Suppose at the design review you were asked to predict the effects of PCB laminate tolerances and etching tolerance on the performance (height, dielectric constant, metal thickness etc etc).All of the above can be done/answered quite well with a modern EM simulator whilst sat at a PC with a can of diet coke and a bag of minstrelsHow would you do it with your VNA?

author: tggzzz
author_rank: Super Contributor
timestamp: November 02, 2014, 12:49:53 pm
content: Quote from: G0HZU on November 02, 2014, 12:16:39 pmPrecisely - although some might claim that "simulation is practice" whereas "modelling is theory".My attitude... Practice without theory is blind fumbling; theory without practice is mental masturbation.

author: G0HZU
author_rank: Super Contributor
timestamp: November 02, 2014, 12:59:41 pm
content: Yes, in reality the filter would be designed and optimised on the simulator. At some point it would be built and tested on a VNA.The number of design iterations can be expected to be far fewer and the time and materials cost will be far less if the simulator is used at the learning/optimising stage of the initial design on the PC.In eurofox's case this would mean modelling stuff up at maybe 20GHz or more. Way out of my comfort zone but I would still want to do it even if it meant making loads of mistakes whilst refining the various models.At some point the models will hopefully become useful and then the learning curve can really take off. It would also help define the requirements spec of any 'real' VNA to hire or purchase

author: Mr Simpleton
author_rank: Unknown
timestamp: November 02, 2014, 01:35:37 pm
content: Rather than spend a fortune on an ancient apparatus that may or may not function as inteded... why not buy a VNWA, and learn the basics of a network analyzer. You will get top-notch support from the designer Tom Bayer, and if you come up with some clever ideas on how to measure stuff he may even include the methode in the next software release. Once you find you have outgrown this thingy, you are much better prepared to get some serious equipment, and you will have no problems sell the VNWA without too much loss!Worst thing that can happen is that you take likening of the little box and decide to keep it

author: G0HZU
author_rank: Super Contributor
timestamp: November 02, 2014, 02:14:29 pm
content: QuoteNormally I would agree with your argument completely but because eurofox has such a specific and singular reason for a VNA I would recommend getting a free 30 day trial of something like Microwave Office from Applied Wave Research or a free trial of Genesys from Agilent before making a VNA purchase.Both have TDR project files included in the examples folder where you can quickly and easily play with ps risetime pulses and transmission lines (or other components) and look at the performance in the time domain if discontinuities are added to less than perfect transmission lines.I think it would also be possible to export 2 port s parameter data from the simulated test circuit (over an xGHz bandwidth) and then do an inverse FFT offline to see how the inv FFT compares to the direct simulation. This way the performance vs VNA bandwidth could be established if a VNA with time domain technology is looking to be purchased. Note I haven't tried doing this export/IFFT/comparison process myself but I think it would be valid.

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: November 02, 2014, 02:21:49 pm
content: Not an electrical engineer , but have been working a few different trades over the past 3-4 + decades , some went to school for and learned a lot on the job .On the subject of getting a little too much tool in the beginning , or any other wrong headed one-way to do things .Different people may need different methods to get a grasp of concepts .Not that I am advising that there shouldn't be some structure to learning something .One of my 1st trades that was technical in nature was auto repair , in the early yrs. of emission controls and computers in cars , I worked in a shop in CA where they did smog testing , some of the gear cost $50,000+ .After some yrs. , I found I could do lots of diagnostics out in the field with basic tools , sometimes quicker than another guy at the shop with a machine that may take 15 min. to make about 10+ connections .Its been a while since reading the original post , but seem to remember that it was just a question about using / acquiring a VNA , without much detail on what for .My main interest in test gear , these days , is ham radio building , repairing , antennas etc.And one of the bits of test gear that I acquired recently was a miniVNA Pro , I got used and discounted .http://miniradiosolutions.com/minivnaproMainly as an antenna analyzer , but knowing that it would serve many functions as I learn more to do repairs & building .Lord Kelvin " If you can not measure it , you can not improve it "I'l add to the questions also , the miniVNA shows phase , both pos. & neg. , what I have not got a grasp on yet is understanding how to use phase in finding antenna problems / solutions ?

author: Howardlong
author_rank: Super Contributor
timestamp: November 02, 2014, 03:02:42 pm
content: Quote from: G0HZU on November 02, 2014, 12:16:39 pmI don't think I'd ever be asked to do such a thing in such a specific way, and if I was I'd say straight they need to hire someone else!My line of work is designing from the product idea down, and bringing that product idea to manufacturing and market, so I wouldn't even think to need to design in such a thing. Instead I'd be looking at how to design something that was fit for purpose at a much higher level rather than being given a very specific set of criteria with little thought for what the final application was.Although I do do multilayer boards up to the low GHz with controlled impedances, the transmission lines tend to be very short (typically a few millimetres at most), low power, and the designs tend to be fundamentally conceptually simple, all being microstrip rather than stripling. About as complex as I've ever needed to fabricate on a PCB are S band power splitters and circularly polarised patch antennas.Despite this I agree with you that I am more than capable of knocking back my fair share of Minstrels washed down with Diet Coke!

author: tggzzz
author_rank: Super Contributor
timestamp: November 02, 2014, 03:06:48 pm
content: Quote from: G0HZU on November 02, 2014, 12:59:41 pmJust so.A real advantage of modelling (as opposed to "mere" simulation) is that when reality diverges from the model (e.g. filter isn't "good enough") then you can form an intelligent estimate of which parameter to change, and by how much.Another real advantage of modelling is that it can help define the boundaries of the possible.

author: tggzzz
author_rank: Super Contributor
timestamp: November 02, 2014, 03:36:03 pm
content: Quote from: Howardlong on November 02, 2014, 03:02:42 pmWhile I strongly agree with that second paragraph, the question posed is a very reasonable and good "thought experiment" designed to expose advantages and disadvantages of different processes.To fit in with your (and to a large extent my) way of working, replace the question with the almost identical...Quote

author: G0HZU
author_rank: Super Contributor
timestamp: November 02, 2014, 04:08:03 pm
content: Sometimes you can learn new ways to desigh things with a decent simulator. Several years ago I designed a new type of band reject filter when playing with Sonnet in my lunch breaks at work. (Diet coke and minstrels) It uses defected ground technology. The idea is to defect the grounds in a multilayer PCB and use this to produce a sharp null at one specific frequency. Eg a notch at about 1.5GHz. I found an old plot of an early production version. See below.Its unique selling points are very low through loss up to about 7GHz (eg about 0.5dB) and very good VSWR. The notch is about 60dB deep. If I tried to design and optimise this concept filter using an iterative approach on a VNA it would have taken weeks or months of work (and lots of PCB prototypes) but I got pretty close using Genesys and Sonnet EM and just a quickly produced PCB.If you used conventional distributed or lumped techniques to produce this filter then it would not work as well up to 7GHz. It would probably have additional re entry notches somewhere around 3 or 4 GHz and this would limit its usefulness on the high side of the notch. But Sonnet EM modelled this new type of filter almost perfectly and I would never have worked out how to produce it unless I could try things quickly and easily on a multilayer PCB in a simulator.The plot below is of a real filter measured on an Agilent VNA and not the original simulation.The company now uses this filter in some transmitter products

author: Howardlong
author_rank: Super Contributor
timestamp: November 02, 2014, 09:34:25 pm
content: If I found myself, hypothetically, needing such a thing, and it was going to cost £20k for some software and a considerable amount of time to get comfortable with the software, I'd outsource it. Thing is, I don't think I'd be taking on a project design that I wasn't confident in being able to deliver myself anyway, you leave yourself pretty exposed financially and reputationally if you do.The expensive software thing is a big problem for one-man-bands. The obvious one for me is Matlab which is obcenely priced unless you're an academic, so I rattle on with Octave, spreadsheets and hacking my own code. As it is my spend on recurrent software licensing is already £3.5k per annum, more than enough for one guy I reckon.Nice filter by the way![edit: I am convinced enough to download Sonnet Lite]

author: G0HZU
author_rank: Super Contributor
timestamp: November 02, 2014, 11:35:22 pm
content: Sonnet is a great bit of softwareHowever, don't be put off by the basic and dated looking GUI. Also, it's worth registering the Lite version to get a higher memory limit.The other tip is to use some of the memory saving tweaks that it offers to keep the overall simulation below the limit of the Lite version. It's very easy to design a layout that needs >1Gb of memory if none of the memory saving tricks are used.But you can do some useful stuff with just 32Mb. I think this is the limit for the Lite version but I can't be sure. At work we have the pro version with unlimited memory which kind of makes me a bit lazy when using it. But this can make the simulation time very long indeed.

author: leafi
author_rank: Regular Contributor
timestamp: November 03, 2014, 06:16:38 am
content: I am not an RF engineer however I agree with KD0CAC John's post.I purchased a VNA TINY from miniradiosolutions.com which is apparently their new model which does up to 3GHz. The I too have a spectrum analyzer with the tracking gen and they can perform S11 and S21 easy enough but you wont get phase. I used mine primarily for antenna tuning thus far and without phase you have to more or less guess at component values. The minivna tiny is a bit slow compared to a real VNA / spectrum analyzer but for around 500 US it is hard to compete with. So far I have only attached a 2.4GHz taoglas antenna to it to see the S11. There were a few strange spike spaces in the full range sweep but it still seemed to give me what I need.Coppermountain seemed to have some nice stuff. I was tempted to purchase one of their vector reflectometers but I just can not justify the expense. ~3000 dollars on something I will only use on very rare projects. Maybe when I win the lotto and 3K is pocket change Ill pick one or two up but for now I just could not make the justification although I was very tempted. Their software looked rather nice on the PC side. I was also tempted to get one off of Ebay but the lowest prices for anything decent was around 4K so. The VNA Tiny even came with SMA calibration kit which was a really nice touch as I didnt have to buy or try to make one. I didnt know it was in there either until I opened the box.Quote from: KD0CAC John on November 02, 2014, 02:21:49 pm

author: eurofox
author_rank: Unknown
timestamp: November 03, 2014, 05:54:18 pm
content: Quote from: Mr Simpleton on November 02, 2014, 01:35:37 pmI just got mine today and with respect to higher frequency I will look into the simulation path like advised by the experts

author: KJDS
author_rank: Super Contributor
timestamp: November 03, 2014, 07:08:23 pm
content: I've "cheated" before by scaling things up physically. On a directional coupler I built one using N-types instead of SMAs and scaled up everything else by the same ratio. Then using time domain on a 20GHz VNA I could see in far more detail the discontinuities that I was trying to tune out.There's no reason why similar techniques couldn't be used for resistive splitters by using larger SMDs, say 2512 or 1206 instead of 0603 or 0402.

author: LogicalDave
author_rank: Regular Contributor
timestamp: May 03, 2016, 01:23:25 am
content: I know this is an old post, but I've been considering getting an NWT500 for home use. However, I bought one of the related bg7tbl devices that sweeps 138MHz-4.4GHz and although it works, and the signal generation is pretty nice, the resolution bandwidth is huge, so you can't resolve any signal detail; everything just looks like a 2MHz blob. How narrow a signal can the NWT500 resolve?

author: RadioDude
author_rank: Newbie
timestamp: June 19, 2016, 11:24:17 am
content: To answer the original post about the MegiQ VNA, here is "A comparison of three Vector Network Analyzers".http://www.gsm-modem.de/M2M/wp-content/uploads/2014/04/IoT-M2M-Cookbook-Harald_excerpt.pdfIt is review of the MegiQ VNA-0440, Rohde & Schwarz ZVL and MiniVNA Tiny. It looks like the megiQ VNA is the same as the Rohde & Schwarz.

author: KJDS
author_rank: Super Contributor
timestamp: June 19, 2016, 01:05:27 pm
content: Quote from: RadioDude on June 19, 2016, 11:24:17 amExcept that we don't know what the stability is. Calibrate, make a measurement, get called into a meeting, come back a few hours later, make another measurement, etc. On the R&S I'd perhaps check the cal once a week but wouldn't redo it for most measurements. We have no idea how stable the MegiQ is. I also don't know what power level variation is available and we do know it won't do a thing below 400MHz which removes a lot of potential customers.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: June 19, 2016, 01:13:37 pm
content: Quote from: RadioDude on June 19, 2016, 11:24:17 amReally?MegiQ VNA-0440:R&S ZVL:The specs are also pretty different:http://www.megiq.com/images/Content/MegiQ-VNA-Specifications-VNA0440-e.pdfhttps://cdn.rohde-schwarz.com/pws/dl_downloads/dl_common_library/dl_brochures_and_datasheets/pdf_1/ZVL_dat-sw_en_5213-8150-22_v0900.pdfSo what makes you think they are the same?

author: chris_leyson
author_rank: Super Contributor
timestamp: June 19, 2016, 01:18:41 pm
content: Hi everyone, first thing this morning I was looking up VNA techniques and found a very interesting MSc thesis by Marcos Martinez and then the very same day RadioDude posts a reply on the forum about VNA advice. Wierd, what are chances of that.But here is a link to the paperhttps://riunet.upv.es/bitstream/handle/10251/34999MartinezArgudo,%20Marcos_Movilidad_Abierto.pdf?sequence=1.It's a really interesting thesis as it replaces directional couplers with bridged-T networks. Link to Choi and Zhao's paper,https://www.researchgate.net/publication/3429059_Compact_mixer-based_1-12_GHz_reflectometer.

author: Marco
author_rank: Super Contributor
timestamp: June 19, 2016, 02:25:51 pm
content: Doesn't TDR/TDT and some software give you a rough VNA?

author: KJDS
author_rank: Super Contributor
timestamp: June 19, 2016, 05:02:30 pm
content: Quote from: chris_leyson on June 19, 2016, 01:18:41 pmWhich is great, but state of the art has been to use a bridge instead of a coupler for at least fifteen years and probably longer than that.

author: chris_leyson
author_rank: Super Contributor
timestamp: June 19, 2016, 05:10:53 pm
content: QuoteWow, I really am out of touch with state of the art VNAs.

author: KJDS
author_rank: Super Contributor
timestamp: June 19, 2016, 06:10:24 pm
content: Quote from: chris_leyson on June 19, 2016, 05:10:53 pmI only know this as I friend introduced me to the bloke in charge of Agilent (or possibly HP) VNA design at a European Microwaves do many years ago. From memory, they were working more using a wheatstone bridge arrangement to 40GHz. Couplers are a nightmare as you go lower and lower in frequency, unless you just want to stay at low frequency.