Smith Chart
en.wikipedia.org
en.wikipedia.org
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).
Say you want 15 dB return loss at some frequency, well there are two impedances points for that. One with the impedance locus outside Z0, and another with the locus encompassing Z0. The latter has broader bandwidth, but that intuition is lost without a Smith or polar plot.
>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.
I have a collection of various RF slide calculation tools. The prized one is rotary sliding Smith Chart.
Still amazed that someone was able to come up with this tool
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...
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.
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://math-fail.com/wp-content/uploads/smith-chart-tattooo....
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.
It's true that today it's rarely used as a calculation tool, but it's still useful as a visualization. I don't think it's obsolete like punch cards.
Preemptive: No, 3D Smith Charts do not obsolete Smith Charts, just like 3D line charts don't obsolete 2D line charts.
You weren't kidding. From 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 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.
Meanwhile, nobody who's not involved in running a computer museum uses punch cards for anything, and there's little or no pedagogical value in continuing to teach IT or CS students about them.