[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.
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.
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.
NFC tags are a frequent target for experimentation, whether simply by using an app on a mobile phone to interrogate or write to tags, by incorporating them in projects by means of an off-the-shelf module, or by designing a project using them from scratch. Yet they’re not always easy to get right, and can often give disappointing results. This article will attempt to demystify what is probably the most likely avenue for an NFC project to have poor performance, the pickup coil antenna in the reader itself.
The tags contain chips that are energised through the RF field that provides enough power for them to start up, at which point they can communicate with a host computer for whatever their purpose is.
“NFC” stands for “Near Field Communication”, in which data can be exchanged between physically proximate devices without their being physically connected. Both reader and tag achieve this through an antenna, which takes the form of a flat coil and a capacitor that together make a resonant tuned circuit. The reader sends out pulses of RF which is maintained once an answer is received from a card, and thus communication can be established until the card is out of the reader’s range. Continue reading “NFC Performance: It’s All In The Antenna”→
Those of us who have bought cheap TinyVNA devices for our RF experimentation will be used to the calibration procedure involving short-circuit, 50 Ω, and open terminations, followed by a direct connection between ports. We do this with a kit of parts supplied with the device, and it makes it ready for our measurements. What we may not fully appreciate at the level of owning such a basic instrument though, is that the calibration process for much higher-quality instruments requires parts made to a much higher specification than the cheap ones from our TinyVNA. Building a set of these high-quality parts is a path that [James Wilson] has taken, and in doing so he presents a fascinating discussion of VNA calibration and the construction of standard RF transmission line components.
We particularly like the way that after constructing his short, load and open circuit terminations using high-quality SMA sockets, he put a custom brass fitting 3D printed by Shapeways on the end of each to make them easier to handle while preserving their RF integrity. If we’d bought a set of terminations looking like these ones as commercial products we would be happy with their quality, but the real test lay in their performance. Thanks to a friend he was able to get them tested on instruments with much heftier price tags, and found them to be not far short of the simulation and certainly acceptable within his 3 GHz range.
Curious about VNAs at the affordable end of the spectrum? We took a look at the TinyVNA, which while it is something of a toy is still good enough for lower frequency measurements.
There was a time when a Vector Network Analyser or VNA was the type of instrument that cost as much as a very fancy car or even a small house. The advent of commodity semiconductors that perform at high RF frequencies coupled with microcontrollers powerful enough to handle the data acquisition and processing might not yet have put those high-perfomance instruments within reach, but at our end of the market it’s opened the possibilities for some useful yet affordable devices. A fresh contender comes from [Jankae], whose LibreVNA tops out at 6 GHz and shows some significant attention to design detail that puts it above some of the budget offerings.
At its heart is the versatile Si5351 multi-way clock generator, accompanied by a pair of MAX2871 phase-locked-loop chips for the higher frequency local oscillators. A switched bank of low-pass filters take care of local oscillator harmonics, and in the receive chain there are ADL5081 mixers feeding a dual conversion IF running at 70 MHz and then 300 kHz. Finally the ADCs are Microchip’s MCP3313, and all is kept in sync by an FPGA and an STM32G431 microcontroller. The main data proccessing is offloaded to a host computer, with a software package and GUI able to be compiled on Windows, Linux, and OSX.
The PCB shows the attention to detail, not least in the power supply arrangements, with every major component receiving its own regulator to ensure no RF makes it down the power rails. It’s clear that a properly made LibreVNA won’t be as cheap as some of its rivals, but we think the corresponding performance hike would make the extra cost worthwhile.
We live in a good time to be an electronics geek. It used to be only the richest or shrewdest among us had a really good oscilloscope, while these days it is entirely feasible to have a scope that would have cost a fortune a few decades ago, a logic analyzer, arbitrary waveform generator, and what would have once been a supercomputer and still not be in debt. One of the cooler pieces of gear for people working on RF electronics is a vector network analyzer (VNA) which used to be exotic, but now can be bought for very little. But what do you do with it? [W2AEW] has the answer.
We always look forward to a video from [W2AEW]. Even if we know about the subject he covers, we usually pick up something new or interesting. Like all of his videos, this one is intensely practical. Not a lot of drawing but plenty of scope shots and experimenting.
It’s never too late in life for new experiences, but there’s a new experience I had a few weeks ago that I wasn’t expecting. I probably received my first piece of test equipment – a multimeter – in the early 1980s, and since then every time I’ve received a new one, whether an oscilloscope, logic analyser, spectrum analyser or signal generator, I’ve been able to figure out how to use it. I have a good idea what it does, and I can figure out whatever its interface may be to make it do what I want it to. My new experience came when I bought a piece of test equipment, and for the first time in my life didn’t have a clue how to use it.
That instrument is a Vector Network Analyser, or VNA, and it’s worth spending a while going through the basics in case anyone else is in the same position. My VNA is not a superlative piece of high-end instrumentation that cost the GDP of a small country, it’s the popular $50 NanoVNA that has a fairly modest frequency range and performance, but is still a functional VNA that can take useful measurements. But I’m a VNA newbie, what does a VNA do? Continue reading “So. You Bought A VNA. Now What?”→