Antenna Measurement In Theory And Practice

If you want to analyze an antenna, you can use simulation software or you can build an antenna and make measurements. [All Electroncs Channel] does both and show you how you can do it, too, in the video below.

The antenna in question is a loop antenna. He uses a professional VNA (Vector Network Analyzer) but you could get away with a hobby-grade VNA, too. The software for simulation is 4NEC2.

The VNA shows the electrical characteristics of the antenna, which is one of the things you can pull from the simulation software. You can also get a lot of other information. You’d need to use a field strength meter or something similar to get some of the other information in the real world.

The antenna simulation software is a powerful engine and 4NEC2 gives you an easy way to use it with a GUI. You can see all the graphs and plots easily, too. Unfortunately, it is Windows software, but we hear it will run under Wine.

The practical measurement is a little different from the simulation, often because the simulation is perfect and the real antenna has non-ideal elements. [Grégory] points out that changing simulation parameters is a great way to develop intuition about — in this case — antennas.

Want to dive into antennas? We can help with that. Or, you can start with a simple explanation.

Continue reading “Antenna Measurement In Theory And Practice”

VNAs And Crystals

Oscillators may use crystals as precise tuned circuits. If you have a vector network analyzer (VNA) — or even some basic test equipment — you can use it to learn the parameters of a crystal. [All Electronics Channel] has the details, and you can see how in the video below.

There was a time when a VNA was an exotic piece of gear, but these days they are relatively common. Crystal parameters are important because crystals have a series resonance and a parallel resonance and they are not at the same frequency. You also may need to know how much loading capacitance you have to supply to get the crystal at the right frequency.

Sometimes, you want to pull the crystal frequency, and the parameters will help you figure that out, too. It can also help if you have a crystal specified as series in a parallel-mode oscillator or vice versa.

If you don’t have a VNA, you can use a tracking signal generator, as [Grégory] shows towards the middle of the video. The quality of a tuned circuit depends on the Q factor, and crystals have a very high Q factor.

We did something similar in 2018. The other way to pull a crystal frequency is a bit extreme.

Continue reading “VNAs And Crystals”

A Lesson In RF Design Thanks To This Homebrew LNA

If you’re planning on working satellites or doing any sort of RF work where the signal lives down in the dirt, you’re going to need a low-noise amplifier. That’s typically not a problem, as the market is littered with dozens of cheap options that can be delivered in a day or two — you just pay your money and get to work. But is there a case to be made for rolling your own LNA?

[Salil, aka Nuclearrambo] thinks so, and he did a nice job showing us how it’s done. The first step, as always, is to define your specs, which for [Salil] were pretty modest: a low noise figure, moderate gain, and good linearity. He also wanted a bandpass filter for the 2-meter amateur radio band and for weather satellite downlinks, and a bias-tee to power the LNA over the coax feedline. The blog post has a detailed discussion of the electrical design, plus some good tips on PCB design for RF applications. We also found the discussion on bias-tee design helpful, especially for anyone who has ever struggled with the idea that RF and DC can get along together on a single piece of coax. Part 2 concentrates on testing the LNA, mostly using hobbyist-grade test gear like the NanoVNA and tiny SA spectrum analyzer. [Salil]’s tests showed the LNA lived up to the design specs and more, making it more than ready to put to work with an RTL-SDR.

Was this more work than buying an LNA? Absolutely, and probably with the same results. But then again, what’s to learn by just getting a pre-built module in the mail?

Understand Your Tools: Finger Exercises

A dip meter is basically a coil of wire that, when you excite it, you can use to tell if something inside that coil is resonating along. This lets you measure unknown radio circuits to figure out their resonant frequency, for instance. This week, we featured a clever way to make a dip meter with a nanoVNA, which is an odd hack simply because a dip meter used to be a common spare-parts DIY device, while a vector network analyzer used to cost more than a house.

Times have changed, and for the better. Nowadays, any radio amateur can pick up a VNA for less than the cost of all but the cheesiest of walkie talkies, putting formerly exotic test equipment in the hands of untrained mortals. But what good is a fancy-pants tool if you don’t know how to use it? Our own Jenny List faced exactly this problem when she picked up a nanoVNA, and her first steps are worth following along with if you find yourself in her shoes.

All of this reminded me of an excellent series by Mike Szczys, “Scope Noob”, where he chronicled his forays into learning how to use an oscilloscope by running all of the basic functions by working through a bunch of test measurements that he already knew the answer to.

It strikes me that we could use something like this for nearly every piece of measuring equipment. Something more than just an instruction manual that walks you through what all the dials do. Something that takes you through a bunch of example projects and shows you how to use the tool in question through a handful of projects. Because these days, access to many formerly exotic pieces of measuring gear has enabled many folks to have gear they never would have had before – and all that’s missing is knowing how to drive them.

A NanoVNA As A Dip Meter

A staple of the radio amateur’s arsenal of test equipment in previous decades was the dip meter. This was a variable frequency oscillator whose coil would be placed near the circuit to be tested, and which would show an abrupt current dip on a moving coil meter when its frequency matched the resonant frequency of what it was testing. For some reason the extremely useful devices seem hard to come by in 2024, so [Rick’s Ham Shack] has come along with a guide to using a nanoVNA in their place.

It’s a simple enough technique, indeed it’s a basic part of using these instruments, with a large sensor coil connected to the output port and a frequency sweep set up on the VNA. The reactance graph then shows any resonant peaks it finds in the frequency range, something easily demonstrated in the video below the break by putting a 20 meter (14 MHz) trap in the coil and seeing an immediate clear peak.

For many readers this will not be news, but for those who’ve not used a VNA before it’s a quick and easy demo of an immediate use for these extremely versatile instruments. For those of us who received our callsigns long ago it’s nothing short of miraculous that a functional VNA can be picked up at such a reasonable price, and we’d go as far as to suggest that non radio amateurs might find one useful, too. Read our review, if you’re interested.

Continue reading “A NanoVNA As A Dip Meter”

Vector Network Analyzer Demo And Teardown

[Kerry Wong], ever interested in trying out and tearing down electrical devices, demonstrates and examines the SV 6301a Handheld Vector Network Analyzer. He puts the machine through its paces, noting that the 7 inch touchscreen is a pretty nice feature for those whose eyesight isn’t quite what it used to be.

The internals are similar to the nanoVNA-F V3, but not identical.

What’s a Vector Network Analyzer (VNA)? It’s not for testing Ethernet or WiFi. It’s aimed at a more classical type of “network”. The VNA tests and evaluates characteristics of electrical networks, especially as related to RF and microwave.

It provides detailed information about properties across a specified frequency range, making it an indispensable tool for advanced work. Tektronix has a resource page that goes into detail about exactly what kinds of things a VNA is good for.

[Kerry] shows off a few different features and sample tests before pulling the unit apart. In the end, he’s satisfied with the features and performance of the device, especially the large screen and sensible user interface.

After all, not every piece of test equipment does a great job at fulfilling its primary function, like the cheap oscilloscope that was a perhaps a little too cheap.

Continue reading “Vector Network Analyzer Demo And Teardown”

The Dipole Antenna Isn’t As Simple As It Appears

Dipole antennas are easy, right? Just follow the formula, cut two pieces of wire, attach your feedline, and you’re on the air.  But then again, maybe not. You’re always advised to cut the legs a little long so you can trim to the right length, but why? Shouldn’t the math just be right? And what difference does wire choice make on the antenna’s characteristics? The simple dipole isn’t really that simple at all.

If you’ve got antenna questions, check out [FesZ]’s new video on resonant dipoles, which is a deep dive into some of the mysteries of the humble dipole. In true [FesZ] fashion, he starts with simulations of various dipole configurations ranging from the ideal case — a lossless conductor in free space with as close to zero diameter conductors as the MMANA antenna simulator can support — and gradually build up to more practical designs. Continue reading “The Dipole Antenna Isn’t As Simple As It Appears”