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Author Topic: Ham Radio uses for a Smith-Chart  (Read 1382 times)
KM3K
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Posts: 395




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« on: October 24, 2017, 02:31:14 PM »

Hello,

I am on our club's schedule to give, in February-2018, a 20-minute talk about the Smith-Chart.
There is no problem here talking about the actual chart itself.

But there is a problem coming up with cases that would be useful for the typical ham.
The only facet I can think of would be related to antenna work.
An example would be to plot the impedance at the end of a transmission-line; here I thinking that a ham would measure that impedance seasonally to see how it may change due to deterioration of coax or insulators or whatever. Then plot the impedance to get a visual picture of how it is changing.
Perhaps another would be to plot feed-point impedances as changes are made to an antenna design.

My hope is that some could suggest other uses a typical ham might apply to a Smith-Chart; of course, credit would be noted in the bibliography for any I may include in my presentation.
73 Jerry KM3K
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N5EG
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« Reply #1 on: October 24, 2017, 03:06:44 PM »

Hi Jerry - I gave this presentation at our club meeting in 2010.  It has a worked out example
application (matching a mobile antenna) with 3 different solutions.

http://www.tapr.org/~n5eg/index_files/RVARC%20Smith%20Chart%20&%20Impedance%20Matching.pdf

-- Tom, N5EG
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NZ4ZN
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Posts: 120




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« Reply #2 on: October 24, 2017, 04:01:31 PM »

Thank you for posting that Tom, very nice explanation!
Ed, NZ4ZN
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N4AST
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« Reply #3 on: October 24, 2017, 04:11:32 PM »

Hi Jerry,  I don't know if I am a typical Ham, but I use the Smith chart quite often.  I use it primarily for antenna matching, but it can be used for other matching problems like matching the input impedance of an RF amplifier circuit.

In the world of antennas and transmission lines, as N5EG did I used it to design matching networks for several mobile antennas.  I use it to determine the settings for "L", "T", and "PI" network antenna tuners for a given impedance.  You can see the effect of open or shorted transmission line stubs on antennas.  You can see the effect of placing a series transmission line of a different Zo in your transmission line.  This is known as "Series Transmission Line Matching".  I recently designed a tuner for an End Fed Half Wave antenna using a rotary inductor and parallel capacitor to match the high impedance of the antenna.

I usually design the antenna with software (Eznec), measure the input impedance with an antenna analyzer to see if it matches what Eznec predicted, and use the Smith Chart to design a matching network.  The Smith Chart software I use: Smith V2.03.  This is by Fritz Dellsperger-Berne University of Applied Sciences.

Gary N4AST
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WB6BYU
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« Reply #4 on: October 24, 2017, 04:19:56 PM »

A good sort of example to work might be to match an antenna by
adding a coax stub on a T connector at the right spot along the feedline.
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W5DXP
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« Reply #5 on: October 24, 2017, 05:00:36 PM »

The current maximum point on ladder-line is (usually) a good place to feed an antenna system. You could use EZNEC to estimate the feedpoint impedance of any non-resonant dipole and then use a Smith Chart to find the current maximum point on the ladder-line tuned feeder. That's the way to match any non-resonant antenna.

You can also demonstrate the use a Smith Chart in designing a stub.
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NR4C
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« Reply #6 on: October 25, 2017, 11:17:49 AM »

If you have access to an modern analyzer that can be projected on a big screen, you might demo a VHF or UHF antenna that you can try several feedline lengths, and trim the antenna to different lengths and show the results on the smith chart.

...bc  nr4c
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G3RZP
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« Reply #7 on: October 25, 2017, 03:26:23 PM »

The best book I know on the subject is "Electronic Applications of the Smith Chart" by Philip H. Smith.

Could someone explain to me what the NON electronic applications of the Smith Chart are, please?
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N4BCD
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« Reply #8 on: October 25, 2017, 04:25:08 PM »

Jerry, two of our local clubs were fortunate to host a gentleman ham (actually a retired Collins engineer) to present his program on Smith Charts.  The first club had a DX focus and slightly more knowledgeable audience.  The second club was more of a general interest club.  He passed out paper Smith charts and briefly talked about what the axes & circles & such were and then in his Texas drawl said "now throw those away and watch this".

He then launched SimSmith (free download) on a laptop with video projection and showed the effects of stubs, increasing line length, frequency sweeps, and real examples of making a source<>load matching easy.

It went over VERY WELL. 

73 & good luck on your program,
 Mark N4BCD
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VK6HP
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Posts: 151




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« Reply #9 on: October 25, 2017, 04:48:27 PM »

In reference to non-electronic uses, one can use a Smith Chart anywhere complex impedance, propagation and reflection are involved, including mechanics and acoustics.  Personally, I've used a Smith Chart to illustrate the behaviour of organ pipes, looking at when and how the pipe becomes generative and the behaviour with various loads presented by the stub (pipe).  As in electronics there are often some approximations of linearity involved when modelling and characterising the physical system.  I can't recall off-hand if it was Smith himself who pointed out that the Chart could also be used in the -R regime with some re-casting.  This turned out to be useful in the pipe situation bearing in mind that, physically, the pipe is often more like a square-wave oscillator and resonator than a linear system.

I've also seen the Chart used for coupled resonator/filter design applications in acoustics. I'm sure there are many other examples.
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