
Smith Chart - benbreen
https://en.wikipedia.org/wiki/Smith_chart
======
willis936
I've found two uses for smith charts: causing students pain and impedance
matching. They're good learning tools but imo it's less of a headache to do
impedance matching in code.

For actual measurements: there is much less ambiguity in a standard
magnitude/phase response, since you actually can see the values of your
independent variable (frequency).

~~~
falcrist
They're quite similar to slide rules in that respect. Learning how to use one
gives you an intuitive grasp of the operations you might otherwise miss (or
not see as clearly), but there are far better tools for doing the actual
computation.

------
etimberg
If anyone wants to see what an implementation of one looks like, I have an old
one I wrote as an extension to Chart.js

[https://github.com/chartjs/chartjs-chart-
smith](https://github.com/chartjs/chartjs-chart-smith)

~~~
CamperBob2
Nice work, but it seems there are no examples of the output images?

~~~
etimberg
You're right, I thought I had added those a while ago. Will add some.

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Merrill
"Remembering Phillip H. Smith on his 100th Birthday" \-
[https://faculty.up.edu/ainan/aps2005inanMarch05.pdf](https://faculty.up.edu/ainan/aps2005inanMarch05.pdf)

>Smith approached a number of technical magazines for publication of his
transmission line diagram; however the acceptance process was slow. Finally,
after two years, Smith’s article describing his chart was published in the
January 1939 issue of Electronics magazine. In a second article, published in
the January 1944 issue of Electronics, Smith incorporated further improvements
into his chart, including its usage alternatively as an impedance chart or an
admittance chart.

~~~
Merrill
In the late '60s, the introduction of PL/I, which had complex numbers as a
primitive type and a math library of functions of complex numbers, made
transmission line calculations much easier.

~~~
GeorgeTirebiter
Fortran 66 had a COMPLEX data type.

------
segfaultbuserr
Alan Wolke (W2AEW) has a good video tutorial (along with his other good radio
electronics tutorials) on YouTube about the basic applications of Smith Chart,
understandable to most radio hobbyists without an electrical engineering
background.

[https://www.youtube.com/watch?v=TsXd6GktlYQ](https://www.youtube.com/watch?v=TsXd6GktlYQ)

------
madengr
No way is the Smith Chart outdated. I use it daily in simulation software and
on the VNA. If a Smith Chart is not shown in a meeting, then that meeting is a
waste of time.

I have a collection of various RF slide calculation tools. The prized one is
rotary sliding Smith Chart.

~~~
krapht
This is so funny to me. At my workplace we preferred magnitude phase plots and
tables. People had to be reminded how to interpret Smith charts

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wigglewoggle
This brings back memories of the microwave lab in school which held the
donated network analyzers ($$$) and was behind a keycard door within another
lab that was behind its own keycard door.

Still amazed that someone was able to come up with this tool

~~~
paulirwin
How times have changed. You can now get a two port (S11/S21) battery-powered
color touchscreen NanoVNA vector network analyzer that can do Smith charts,
SWR, and all kinds of other things for under $40. I use one to analyze ham
radio antennas and it's not perfect, but works well enough for my needs and is
an incredible value. The firmware for it is open source, too.

~~~
segfaultbuserr
Its performance is nowhere comparable to a real VNA, those VNAs made by
Hewlett-Packard in the late 80s are still the golden standard for many labs.

But NanoVNA is great value for the money for anyone interested in radio
electronics! For $50, almost nothing beats a NanoVNA, and it's much more
effective than the traditional sweep generator setup. You get complex S11/S21
and 900 MHz bandwidth [0], good for measuring complex impedance, the insertion
loss of the coax, the frequency response of filters, SWR of antennas, and even
basic Time-Domain Reflectometry. The firmware is available under GPLv3 for
hacking as well.

I recently used it to experiment different ferrite RF transformers for my
homebrew radio receiver, and to characterize frequency response of inductors.

The only thing to beware - since it's a "almost" free hardware design (i.e.
FOSS firmware + a block diagram for hardware, only the PCB layout is not
available), there are a number of low-quality clones that use low quality
components and don't include proper shielding. I recommend hugen79's version
("NanoVNA-H"), he is not the original designer (it was designed by edy555
[2]), but hugen79's version is currently the most common source with
reasonable quality, see the picture for comparison. [1]

[0] > 600 MHz uses higher-order harmonics, and is less reliable, but still
better than nothing.

[1]
[https://github.com/hugen79/NanoVNA-H/blob/master/doc/clone.j...](https://github.com/hugen79/NanoVNA-H/blob/master/doc/clone.jpg)

[2] [https://github.com/ttrftech/NanoVNA](https://github.com/ttrftech/NanoVNA)

~~~
topspin
There is a forthcoming NanoVNA version 2 that will have improved dynamic range
due to better down mixers and added audio op amps.

I think the whole NanoVNA eruption (including the clones and alternatives) is
outstanding. I believe there is a large unsatisfied demand for low performance
instruments that are sufficient for experimentation below ~3 GHz. There are a
lot of used instruments around that are large, heavy and usually need service,
and there are a number of built-down-to-a-price entirely proprietary
instruments from Asia, but nothing beats a device that fits in your hand, runs
free code from GitHub and costs so little that you can fry it accidentally and
not care much.

~~~
segfaultbuserr
> _There is a forthcoming NanoVNA version 2_

I've already heard about it, looking forward to the new one.

> _I believe there is a large unsatisfied demand for low performance
> instruments_

Yeah, there's a huge demand for low performance instruments of all types.

And a surprising amount of such equipment can be built using low-cost parts
thanks to progress in semiconductors - very limited performance, often
uncalibrated, sure, but valuable for experimenters. For example, a 1 GHz
active oscilloscope probe for $50 [0].

I think the critical part is not simply the possibility of _building_ them,
but making them easily _available_. If you read the old homepage on the web,
or old electronics magazines, you can see a lot of similar DIY projects. But a
lot of those DIY projects are not very repeatable.

But in recent years, I think the rise of the web and the popularity of free
and open source software and hardware design is a game changer in this aspect.
Today, I can download a PCB design from GitHub and send it to a factory for
assemble simply by a few mouse clicks, and a week later, I can get a
prototype. Even if the original designer stopped working on it, others in the
community can contribute easily and carry on.

> _but nothing beats a device that fits in your hand, runs free code from
> GitHub and costs so little that you can fry it accidentally and not care
> much._

Can't agree more.

[0] [http://blog.weinigel.se/2016/02/26/ghz-differential-
probe.ht...](http://blog.weinigel.se/2016/02/26/ghz-differential-probe.html)

~~~
cushychicken
That OSHW differential probe is really neat. Thanks for sharing!

------
BrianHenryIE
We had fondness for Smith Charts when we were in college. We came across cakes
and tattoos online:

[http://math-fail.com/wp-content/uploads/smith-chart-tattooo....](http://math-
fail.com/wp-content/uploads/smith-chart-tattooo.jpg)

[https://www.microwaves101.com/uploads/SmithCake-
NITT.jpg](https://www.microwaves101.com/uploads/SmithCake-NITT.jpg)

------
blackguardx
Smith charts are really versatile. You can use them for all sorts of RF
circuit design tasks, as a complex number calculator, and perhaps more
importantly a way to visualize impedance. It is almost how people think in
their native language, you can visualize how impedances will interact using
the smith chart in your head.

------
foxes
Looks like a Mobius transformation which is rational function f : C -> C, on
the complex plane, of the form

f(z) = (a z + b) / (c z + d).

The key feature is that this is a conformal transformation which means it
preserves angles (between curves).

Reading it a bit more I guess thats clear.

------
Vysero
Ah yes the Smith Chart. The physics equivalent to programming punch cards.

~~~
jjoonathan
Punch cards are made thoroughly obsolete many orders of magnitude over by
modern storage and IO technologies. What replaced Smith Charts? The >$100k
only-a-few-years-old VNAs next room over still plot S11 and S22 on Smith
Charts and I'd bet you an entire VNA that this will still be the case in 10
years.

Preemptive: No, 3D Smith Charts do not obsolete Smith Charts, just like 3D
line charts don't obsolete 2D line charts.

~~~
kstrauser
> Punch cards are made thoroughly obsolete many orders of magnitude over by
> modern storage and IO technologies.

You weren't kidding. From
[https://en.wikipedia.org/wiki/Punched_card_input/output](https://en.wikipedia.org/wiki/Punched_card_input/output)
:

> If all columns of an 80 column card encode information this translates to
> approximately 2,500 characters per second (CPS).

According to [https://www.techradar.com/reviews/samsung-970-evo-
plus](https://www.techradar.com/reviews/samsung-970-evo-plus) a 970 EVO Plus
SSD is about 1,400,000 times faster. Wow. I would love to go back a few years
and blow young me's mind.

------
LandoCalrissian
I still you the smith chart on my NanoVNA for ham radio.

------
person_of_color
RF/Analog people are wired differently!

~~~
GeorgeTirebiter
I'm pretty sure RF people have no wires .... (ducking into a Faraday
Shield...)

~~~
madengr
Plumbed with waveguide

