[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...

[2] 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...

[cushychicken]

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

[csboyer]

Copper mountain has some decent VNAs given the price point.

[mNovak]

Above a couple GHz, VNAs are still $$$. With mm-wave being the hot topic now, you're still looking close to $100k