Author Topic: Smitih Charts, still relevant in 2024?  (Read 3789 times)

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Offline pdenisowski

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Re: Smitih Charts, still relevant in 2024?
« Reply #25 on: June 22, 2024, 09:26:54 am »
I don't understand what a Smith Chart really helps with - and never felt I needed one.

I feel like I've always missed something here...
Explain it like I'm 5 please?

When 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"
Test and Measurement Fundamentals video series on the Rohde & Schwarz YouTube channel:  https://www.youtube.com/playlist?list=PLKxVoO5jUTlvsVtDcqrVn0ybqBVlLj2z8
 
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Offline Tation

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Re: Smitih Charts, still relevant in 2024?
« Reply #26 on: June 23, 2024, 06:04:50 am »
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?

An 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.
« Last Edit: June 23, 2024, 06:48:01 am by Tation »
 

Offline Georgy.Moshkin

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Re: Smitih Charts, still relevant in 2024?
« Reply #27 on: June 23, 2024, 07:24:04 am »
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.
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Offline RoGeorge

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Re: Smitih Charts, still relevant in 2024?
« Reply #28 on: June 23, 2024, 07:40:09 am »
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. 
« Last Edit: June 23, 2024, 08:05:00 am by RoGeorge »
 

Online coppercone2

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Re: Smitih Charts, still relevant in 2024?
« Reply #29 on: June 23, 2024, 08:01:06 am »
listening to someone mocking you in any way involving a corporate entity knowing how to do things is not a good idea

work is like french fashion club

you 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

« Last Edit: June 23, 2024, 08:08:57 am by coppercone2 »
 
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Online coppercone2

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Re: Smitih Charts, still relevant in 2024?
« Reply #30 on: June 23, 2024, 08:13:25 am »
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.

« Last Edit: June 23, 2024, 08:18:57 am by coppercone2 »
 
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Online Wallace Gasiewicz

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Re: Smitih Charts, still relevant in 2024?
« Reply #31 on: June 23, 2024, 01:43:13 pm »
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. 
I cannot find one, still looking.....

Quote from: bson on Yesterday at 02:18:26 am
I don't understand what a Smith Chart really helps with - and never felt I needed one.

I feel like I've always missed something here...
Explain it like I'm 5 please?

When 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"
Is 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 example       
The 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.
 

Offline pdenisowski

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Re: Smitih Charts, still relevant in 2024?
« Reply #32 on: June 23, 2024, 02:38:02 pm »
Is that a Smith Chart I see in your Signature?   

Yes :)  I was looking for a "logo" to use and thought that nothing says "RF Test and Measurement" quite as clearly and unambiguously as a Smith chart :)

It's actually a redraw of part of a mural at the R&S headquarters in Munich

« Last Edit: June 23, 2024, 02:42:26 pm by pdenisowski »
Test and Measurement Fundamentals video series on the Rohde & Schwarz YouTube channel:  https://www.youtube.com/playlist?list=PLKxVoO5jUTlvsVtDcqrVn0ybqBVlLj2z8
 
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Offline pdenisowski

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Re: Smitih Charts, still relevant in 2024?
« Reply #33 on: June 23, 2024, 02:45:59 pm »
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.

I'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 ....
« Last Edit: June 23, 2024, 02:47:30 pm by pdenisowski »
Test and Measurement Fundamentals video series on the Rohde & Schwarz YouTube channel:  https://www.youtube.com/playlist?list=PLKxVoO5jUTlvsVtDcqrVn0ybqBVlLj2z8
 
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Offline gf

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Re: Smitih Charts, still relevant in 2024?
« Reply #34 on: June 23, 2024, 03:24:58 pm »
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 ....

If it does not measure and report the network parameters (such as Z-, y-, h-, S-parameters, etc.) of a N-port DUT, then I would not call it VNA.
 
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Online W4PJBTopic starter

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Re: Smitih Charts, still relevant in 2024?
« Reply #35 on: June 23, 2024, 03:41:57 pm »
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!
 
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Offline joeqsmith

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Re: Smitih Charts, still relevant in 2024?
« Reply #36 on: June 23, 2024, 04:04:55 pm »
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



Offline joeqsmith

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Re: Smitih Charts, still relevant in 2024?
« Reply #37 on: June 23, 2024, 04:23:07 pm »
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. 

Offline joeqsmith

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Re: Smitih Charts, still relevant in 2024?
« Reply #38 on: June 23, 2024, 05:55:10 pm »
An impedance matching network definitely does not use a resistor, that's wasted power.

I 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.   

« Last Edit: June 23, 2024, 05:58:41 pm by joeqsmith »
 
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Offline coppice

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Re: Smitih Charts, still relevant in 2024?
« Reply #39 on: June 23, 2024, 06:02:18 pm »
An impedance matching network definitely does not use a resistor, that's wasted power.
I disagree.  It's just one more tool in the bag of tricks.
3 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.
 

Offline Joel_Dunsmore

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Re: Smitih Charts, still relevant in 2024?
« Reply #40 on: June 23, 2024, 07:31:02 pm »
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.
 
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Offline Joel_Dunsmore

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Re: Smitih Charts, still relevant in 2024?
« Reply #41 on: June 23, 2024, 07:33:52 pm »
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).
 
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Offline joeqsmith

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Re: Smitih Charts, still relevant in 2024?
« Reply #42 on: June 23, 2024, 07:52:13 pm »
Welcome back Mr Dunsmore.

Online coppercone2

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Re: Smitih Charts, still relevant in 2024?
« Reply #43 on: June 23, 2024, 09:33:43 pm »
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
« Last Edit: June 23, 2024, 09:45:42 pm by coppercone2 »
 
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