Smitih Charts, still relevant in 2024?  - Page 1
Forum section: electronics / testgear

author: W4PJB
author_rank: Regular Contributor
timestamp: June 18, 2024, 04:44:20 pm
content: A little backstory on this question. Recently I met with a seller to look at an HP 8714 ET network analyzer. The seller was a retired engineer from, let's just say, a large radar company that we've all heard of.I asked if the unit had a Smith Chart, and he literally laughed at the idea of still using one. According to the seller, nobody in his former employer used Smith Charts for decades, and even remarked it would be laughable among his peers to use one.Now I'm certainly no EE, just an idiot learning electronics who also likes playing with radio and antenna systems. I'm sure there is a lot a VNA can do I'm not familiar with (thus the reason to get one, to learn) beyond what a Smith Chart can produce. So, are Smith Charts really a thing of the past in most professional environments? Or do they still find common use by those whoactuallydo this for a living?Of course, it's also possible he was simply downplaying the fact that his unit didn't have one, so I would still buy it (I didn't). But it did get me to wondering

author: ZigmundRat
author_rank: Regular Contributor
timestamp: June 18, 2024, 05:38:05 pm
content: Why wouldn’t it be? Tabular data does not give you the visual representation and intuitive insights that the Smith Chart provides. You can find complex impedance and reflection coefficients at a glance. I think your engineer was a snooty know it all type that wanted to hold their ‘superior’ knowledge over you.

author: paul@yahrprobert.com
author_rank: Regular Contributor
timestamp: June 18, 2024, 05:42:51 pm
content: The Smith chart is a mapping from the complex reflection coefficient (the rectangular grid) to the complex impedance Z=(ZL-Z0)/(ZL+Z0). In the bad old days of slide rules it would take you quite a while to do that complex arithmetic by hand, and so Smith charts were very handy. Nowadays with computers you don't need Smith charts. Some people still like them as a way of visualizing things, but if you're handy with Matlab, Octave, or Python you can do things quicker and way more accurately.While we're at it, lets get rid of VSWR and just talk about reflection coefficients (voltage or power).

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: June 18, 2024, 07:44:03 pm
content: HP 8714 HAS a Smith Chart

author: Bud
author_rank: Super Contributor
timestamp: June 18, 2024, 09:01:22 pm
content: The "engineer" you spoken to was a clueless moron. Likely was a paper pusher, a mechanic or a janitor at the "large radar company that we've all heard of".

author: tautech
author_rank: Super Contributor
timestamp: June 18, 2024, 09:20:43 pm
content: Quote from: Bud on June 18, 2024, 09:01:22 pmPrecisely.Smith tells us what other sweeps cannot.From ~900 MHz Yagi:

author: W4PJB
author_rank: Regular Contributor
timestamp: June 18, 2024, 09:31:40 pm
content: Quote from: Wallace Gasiewicz on June 18, 2024, 07:44:03 pmThe ET model (reflection/transmission)? Or only the ES model (S parameter)? We looked through the menu briefly and could not find it. Obviously, he would have never used it if it was there anyway.

author: W4PJB
author_rank: Regular Contributor
timestamp: June 18, 2024, 09:37:22 pm
content: Quote from: paul@yahrprobert.com on June 18, 2024, 05:42:51 pmI think this was his point. I have no experience with any of those, so that's where my ignorance lies.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: June 18, 2024, 09:47:16 pm
content: Mine is an HP 8713 which I upgrades to 8714 with a EPROM change, You should read a little about these things before you buy.Here is a short Keysight Summary of the 8714 ET it includes Smith Charts:https://www.keysight.com/us/en/product/8714ET/rf-network-analyzer-tr.html

author: David Hess
author_rank: Super Contributor
timestamp: June 18, 2024, 10:04:19 pm
content: If was regularly doing RF impedance matching, then I would be regularly using a Smith chart.

author: W4PJB
author_rank: Regular Contributor
timestamp: June 18, 2024, 10:07:07 pm
content: Quote from: Wallace Gasiewicz on June 18, 2024, 09:47:16 pmThanks! I passed on this unit (price was right and it was local, only reason it was on my radar) and actually purchased an 8753C w/ 85046A S-Parameter test set last night. Seemed like a much better deal and was already upgraded to an LCD screen. The screen on the 8714 I looked at was pretty dim and burned in.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 19, 2024, 12:30:37 am
content: Quote from: paul@yahrprobert.com on June 18, 2024, 05:42:51 pmI don't see why you couldn't have your cake and eat it too. Or, why you wouldn't. I wouldn't want to trade in an XY graph on an oscilloscope for some digital readouts. Same for the SA, logic analyzer.... I would rather see the waveform and for complex impedances, Smith.

author: Georgy.Moshkin
author_rank: Frequent Contributor
timestamp: June 19, 2024, 03:23:51 am
content: When we need to visualize complex number, we can use polar plot.E.g., in OctaveCode:handle1=plot(real(s11), imag(s11), 'Color',[1.0,0,0]);Simply using real part of s11 for x coordinates, and imaginary part for y coordinates.This graph also can be called a Smith chart, we can add constant resistance circles, stability circles, etc.There is no need to eliminate Smith chart, as well as polar coordinate systemSmith chart is used in a lot of books and recognized by many people. It may help to remember some concepts. E.g., see here is Smith chart visualization of patch antenna inset length tuning compared to patch dimensions tuning:https://youtu.be/v8uxhbu36Ug?si=GXQMQTdlT_ddQQCy&t=32When we tune inset length, we jump between resistance circles (S11 curve radius changes)And when we change patch dimensions, we tune resonant frequency (point moves along S11 curve)Maybe seller meant that Smith charts are no longer used in paper form to design matching circuits. A lot of CAD programs provide polar plots and call them Smith charts. Some hatred toward Smith charts is caused by unnecessary complication: drawing all those circles at different offsets and pushing into student heads. Maybe teachers should have used simple polar plots without all those circles and terminology first. So, if Seller doesn't like Smith charts, it's not his fault!Smith chart would be especially handy if I design series-feedback oscillator, tunable impedance block (measuring S22 for FET while tuning Vgs bias).

author: tautech
author_rank: Super Contributor
timestamp: June 19, 2024, 07:37:25 am
content: Quote from: Georgy.Moshkin on June 19, 2024, 03:23:51 amAgain:Quote from: tautech on June 18, 2024, 09:20:43 pmA Smith and a Polar, add a marker and which provides more info ?

author: pdenisowski
author_rank: Super Contributor
timestamp: June 19, 2024, 09:22:38 am
content: Out of the215videos I have on the Rohde & Schwarz YouTube channel, the most viewed, most commented on, and most liked video is the one on the Smith ChartAnd yes, a lot of our customers still use the Smith Chart

author: pdenisowski
author_rank: Super Contributor
timestamp: June 19, 2024, 09:33:40 am
content: Quote from: W4PJB on June 18, 2024, 04:44:20 pmIt's very hard for me to imagine a VNA that doesn't have a Smith Chart display. R&S is credited with manufacturing the first commercial network analyzer (the Z-g Diagraph) over 60 years ago and eventhatinstrument had a Smith Chart display

author: Georgy.Moshkin
author_rank: Frequent Contributor
timestamp: June 19, 2024, 09:45:41 am
content: Hey, tautech, I think you've got me wrong. I see polar and Cartesian plots on your images.. And what I was saying is that polar plot = Smith chart. And it's probably how it's implemented on most of VNAs firmware.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 19, 2024, 12:53:09 pm
content: Quote from: Georgy.Moshkin on June 19, 2024, 09:45:41 amUsing your logic, polar plot = Smith chart = Cartesian plot.QuoteI have an HP8754A from the 1970s. It has no firmware. There are overlays that you insert over the CRT to get the different graph types. There is a mechanical switch that selects polar or rectangular.When I wrote the software for it, I map everything to an X-Y graph. Like the 8754A, I use overlays that map over the top of the X-Y graph. A technique I still use with my current software.

author: pdenisowski
author_rank: Super Contributor
timestamp: June 19, 2024, 02:10:42 pm
content: Coincidentally, I was just using a Smith Chart this morning for a video I'm working on ("Measuring Antennas with the ZPH") so I thought I would share a picture on my "work" Instagram account as well.https://www.instagram.com/p/C8ZmxqSgWN2

author: DaJMasta
author_rank: Super Contributor
timestamp: June 19, 2024, 07:04:13 pm
content: When I first got introduced to using smith charts, I found them to be one of the best examples of data visualization in charts that I knew of. Data visualization, even without analysis, let's us - humans evolved for visual pattern recognition - pull a lot more meaning out of a dataset than when presented as a table, a series of numbers, or some other basic formats. Your basic trend chart or scatter plot engages our understanding so much more than the raw values, and it's astounding how much useful information is easily gleaned from a smith chart, especially given the relatively modest requirements for plotting data points on one. A plot that shows impedance matching over frequency that can be normalized to virtually any system impedance, shows meaningful information out towards the extremes, and doesn't just give you match/mismatch information but tells you how so that you can make adjustments to the DUT.Incredibly practically useful for anyone needing to match RF elements all available at a glance, and the absolute basics of relative match vs. mismatch can be see at a glance by someone with no understanding of reactance or how points are plotted on it. Really top tier visualization/user interface technology.

author: tautech
author_rank: Super Contributor
timestamp: June 19, 2024, 08:29:45 pm
content: Quote from: Georgy.Moshkin on June 19, 2024, 09:45:41 amTrace/Sweep, yes.Just as Mag Loss and SWR sweeps are very similar yet in all cases addition of markers gives additional info at marker frequencies.Smith and Polar are the same but their use depends on the info you need from them where Smith is superior.To get even more precise detail scaling can be adjusted like using the screen overlays that Joe showed for his old analyzer.In modern analyzers we just adjust the display scaling to see the detail.

author: radiohomebrewer2000
author_rank: Contributor
timestamp: June 20, 2024, 11:58:15 pm
content: I think Smith Charts are still valuable especially for someone learning radio electronics. It will help you learn complex impedance and what it is made of: inductive reactance, capacitive reactance, and resistance.I recently got some Smith Chart paper to draw some Smith Charts. Found a lot of videos of Smith Charts on YouTube. I did this so it would give me a better understanding of the Nano VNA I got. But I also want to get into designing my own impedance matching networks. So, I think knowing Smith Charts will help.I am the type of person who prefers to draw his schematics with pencil on graph paper and then take a photo of it instead of drawing it via some software. But, I am an amateur - not an engineer.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: June 21, 2024, 12:44:40 am
content: It's way easier to do impedance matching with a Smith Chart tool than without one.

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 21, 2024, 11:54:33 am
content: I'm wondering if the engineer in the OP was referring to the pencil-and-paper approach to matching network designs by scribing arcs on a smith chart. That certainly is rare nowadays. But I've never seen a VNA that doesn't have a smith chart display.Or maybe they only worked with scalar network analyzers?

author: bson
author_rank: Unknown
timestamp: June 22, 2024, 02:18:26 am
content: I don't understand what a Smith Chart really helps with - and never felt I needed one.Certainly not impedance matching? I mean, say I have source impedance of 50+j0Ω, a line of 50-j7Ω, and a load of 45-j20Ω. So matching them requires 5+j27Ω which is a resistor and an inductor. This is kind of elementary, no? If I use the VNA to measure the impedances, isn't the impedance discrepancy obvious? Of course, some devices like antennas don't have a fixed impedance but vary with frequency, usually shifting from inductive to capacitive at the resonant frequency - so can't be matched over a wide band, but how would a Smith Chart help with this?I feel like I've always missed something here...Explain it like I'm 5 please?

author: pdenisowski
author_rank: Super Contributor
timestamp: June 22, 2024, 09:26:54 am
content: Quote from: bson on June 22, 2024, 02:18:26 amWhen I first released my "Understanding the Smith Chart" video I had numerous engineers (privately!) tell me "I've been in RF for X years / decades and I never understood what the Smith Chart was for"

author: Tation
author_rank: Regular Contributor
timestamp: June 23, 2024, 06:04:50 am
content: Quote from: bson on June 22, 2024, 02:18:26 amAn impedance matching network definitely does not use a resistor, that's wasted power. Also the 50-7j Ohm line impedance is what? The characteristic impedance of the line (quite lossy indeed)? the impedance seen at the line when loaded? with what? I cannot understand at all your "elementary" and "obvious" calculations.

author: Georgy.Moshkin
author_rank: Frequent Contributor
timestamp: June 23, 2024, 07:24:04 am
content: Is Smitch Chart relevant in 2024? Yes, because it used in many books, measurement devices, RF CAD programs, datasheets.And it doesn't require too much time to learn.

author: RoGeorge
author_rank: Super Contributor
timestamp: June 23, 2024, 07:40:09 am
content: My question is, does anybody knows any model of a VNA that does not have Smith chart representation?Name it please. Asking because I'm not much into RF, and don't know what instruments are out there. It is a genuine question, not rhetorical. If it exists, I'll be curious to look at such an instrument's specs/manual.

author: coppercone2
author_rank: Super Contributor
timestamp: June 23, 2024, 08:01:06 am
content: listening to someone mocking you in any way involving a corporate entity knowing how to do things is not a good ideawork is like french fashion clubyou get all sorts of deranged arguments, like about looking at hex code. There usually isent a magic new method that's so alien it blows your mind. That only happens when someone is hyper focused on 1 thing that suddenly they think some specific subset of something is the only important thing. Maybe it is, for whatever projects that company is working on at the moment. They are often pigeon holed into something so specific someone else sees their work iterations as the same thing, then of course they see the 'bigger picture' as useless. Its like someone that only interested in godzillas left testicle lol

author: coppercone2
author_rank: Super Contributor
timestamp: June 23, 2024, 08:13:25 am
content: also, are you sure you did not come across someone in sales?its possible they had no idea what a smith chart is, or what that equipment is, but they wanted you to buy it, perhaps you forgot to low ball them first. This way, if they say whatever you are interested in is obsolete and no one uses it anymore, they can sell you the thing that they have.Does that sandwich have tomato on it? No, there is no tomato on it. Dieticians said that tomato is bad for you, this sandwich is fine. Seat warmers? No one ever uses that, its the least used features in cars, believe me im a car salesman. Saul goodman montage moment.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: June 23, 2024, 01:43:13 pm
content: Quote from: RoGeorge on June 23, 2024, 07:40:09 amI cannot find one, still looking.....Quote from: pdenisowski on June 22, 2024, 09:26:54 amIs that a Smith Chart I see in your Signature?I have used my VNA to help me when I was building a Mag Loop Antenna.... Just one exampleThe Smith Chart Function helps a lot when evaluating the freq range of antenna when you wear out your slide rule, It gives a nice visual to represent your "Network" frequency response. The Smith Chart Function is included in lesser test equipment like antenna analyzers. Extremely useful. The chart is included in the material to be studied for HAM license testing.

author: pdenisowski
author_rank: Super Contributor
timestamp: June 23, 2024, 02:38:02 pm
content: Quote from: Wallace Gasiewicz on June 23, 2024, 01:43:13 pmYesI was looking for a "logo" to use and thought that nothing says "RF Test and Measurement" quite as clearly and unambiguously as a Smith chartIt's actually a redraw of part of a mural at the R&S headquarters in Munich

author: pdenisowski
author_rank: Super Contributor
timestamp: June 23, 2024, 02:45:59 pm
content: Quote from: RoGeorge on June 23, 2024, 07:40:09 amI'd like to know this too. Not sure if it counts as a "VNA" or not*, but I have a vector voltmeter that only has two meter type indicators*I would say it doesn't count, especially because it lacks sources, directional couplers, etc. but it can simultaneously measure magnitude and phase ....

author: gf
author_rank: Super Contributor
timestamp: June 23, 2024, 03:24:58 pm
content: Quote from: pdenisowski on June 23, 2024, 02:45:59 pmIf it does not measure and report thenetwork parameters(such as Z-, y-, h-, S-parameters, etc.) of a N-port DUT, then I would not call it VNA.

author: W4PJB
author_rank: Regular Contributor
timestamp: June 23, 2024, 03:41:57 pm
content: I have to admit, I had intended this as a bit of a Socratic question, rather than a yes/no. But wow, I did not expect this thread to blow up so much!Regarding the seller, yes, he was a legit engineer at a radar company. That said, it's not uncommon (especially in very large companies) for people to hyper specialize and have a very narrow scope of anything outside of their area. He was using it to measure attenuators he was selling, and perhaps that's all he did for the last 20 years in corporate as well. In which case, you're probably looking at the same screen, all day, every day.Of course, he had something to sell and like a used car salesman who's only got one to sell, his was going to be the best. I'm sure it had a Smith chart but he sure as heck didn't know where to find it. And I wasn't going to buy a piece of test equipment from someone that doesn't know how it works. After all, how can someone like that guarantee that everything works?Very happy with the clean 8753C I found later that evening.Thanks for all of the replies!

author: joeqsmith
author_rank: Super Contributor
timestamp: June 23, 2024, 04:04:55 pm
content: I bought an AD8302 evaluation board which can measure gain and phase. I was looking at using it to measure VSWR in the HF ham bands. I never plotted any data from it onto a Smithchart but it was certainly possible. In the end, I ditched measuring the phase and went with two AD8307 log amp eval boards that I mapped onto a few virtual Bird analog meters (see video).There are similar products that the hams use today that support vectors.http://www.telepostinc.com/We used to have an HP4194A gain phase analyzer where I worked. I don't recall it supporting Smith but that's going back 35 years or so. HP certainly had VNAs at that time and made the distinction that this product was not a VNA.https://www.testequipmenthq.com/datasheets/Keysight-4194A-Datasheet.pdf

author: joeqsmith
author_rank: Super Contributor
timestamp: June 23, 2024, 04:23:07 pm
content: Also, to further smear the lines of what is a VNA... I have an HP 3589A Spectrum/Network analyzer. While I (and HP apparently) don't consider it a VNA, they support using an external test set, or in my case an external directional coupler. With this we can measure S11. The instrument even includes Smith and supports some simple calibration.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 23, 2024, 05:55:10 pm
content: Quote from: Tation on June 23, 2024, 06:04:50 amI disagree. It's just one more tool in the bag of tricks. Consider that impedance matching is not constrained to antennas and power amplifiers. We even use it when we terminate digital signals. Let me provide you with a simple example. In this video I am using a low cost VNA to measure a power distribution network (PDN). Normally you would design this network for a flat impedance. Watching at 30 minutes in:https://youtu.be/Y8ouApeex78?t=1947,I am using a target impedance of 10 ohms. For the demonstration, I am using a plugin breadboard with various axial parts for the bypass. Obviously this is not anything you would ever do in real life but that's not the point. Rather it was to go over the techniques behind tuning the network.

author: coppice
author_rank: Super Contributor
timestamp: June 23, 2024, 06:02:18 pm
content: Quote from: joeqsmith on June 23, 2024, 05:55:10 pm3 resistors in a Y is the commonest matching network you'll see, used in millions of cheap TV antenna splitters. If it stops reflections it has achieved a match. Its just not the most efficient match.

author: Joel_Dunsmore
author_rank: Regular Contributor
timestamp: June 23, 2024, 07:31:02 pm
content: The smith chart is just another representation of reflection, but it has the advantage of telling you if the impedance mismatch is following a series or shunt reactive element and whether it is inductive or capacitive. You example of the lines being 50 -j7 is a good example: if we look at this on the Smith chat, and over a broader range, we can tell whether it is a capacitive or inductive discontinuity that is giving you the reactive portion (for an example like that one, you likely have a connector discontinuity at the input as the loss of coax is low so it's imaginary part is small if there are no other discontinuities). Same at the far end; measured over a broader range of frequencies will tell you if it is following a series/shunt inductive/capacitive trajectory at a glance, and you can then quickly deduce the best matching network.

author: Joel_Dunsmore
author_rank: Regular Contributor
timestamp: June 23, 2024, 07:33:52 pm
content: Depends on the purpose of the matching. I had a design of amplifier which had too much low-end gain and was only conditionally stable; A little lossy matching inter-stage made it unconditionally stable and the matching was used to flatten the amplitude response (better matching at high frequency).

author: joeqsmith
author_rank: Super Contributor
timestamp: June 23, 2024, 07:52:13 pm
content: Welcome back Mr Dunsmore.

author: coppercone2
author_rank: Super Contributor
timestamp: June 23, 2024, 09:33:43 pm
content: the proper engineering methodology is"does the extra loss of the matching stage bring the loss budget to an unacceptable level?"I think that is how you wanna think about it when you are problem solving for someone to develop a engineering solution. There might be something else that can be changed to reduce loss or increase power to allow for resistance to be used. For instance, a slightly better cable. Some people will say thats OK. It might even make it someone elses problem if they agree to your spec.of course if your lazy and use resistance by default, someone more diligent in research and development might steal your customers if the price is right