A 1990s VNA Gets An LCD

January 10, 2026 by Jenny List 8 Comments

A Vector Network Analyser, or VNA, is the ultimate multi-tool of RF test equipment. They can now be had in not very capable form for almost pocket money prices, but the professional-grade ones cost eye-watering sums. Enough to make an older VNA for a few hundred on eBay a steal, and [W3AXL] has just such a device in an HP 8714C. It’s the height of 1990s tech with a floppy drive and a green-screen CRT, but he’s homing right in on the VGA monitor port on the back. Time for a colour LCD upgrade!

There are two videos below the break, posted a year apart, because as we’re sure many of you will know, events have a habit of getting in the way of projects. In the first, we see the removal of the CRT module and safe extraction of its electronics, followed by the crafting of a display bezel for the LCD. Meanwhile, the second video deals with the VNA itself, extracting the VGA signal and routing it forward to the new module. Continue reading “A 1990s VNA Gets An LCD” →

The Unreasonable Effectiveness Of The Fourier Transform

January 7, 2026 by John Elliot V 32 Comments

A talk, The Unreasonable Effectiveness of the Fourier Transform, was presented by [Joshua Wise] at Teardown 2025 in June last year. Click-through for the notes or check out the video below the break for the one hour talk itself.

The talk is about Orthogonal Frequency Division Multiplexing (OFDM) which is the backbone for radio telecommunications these days. [Joshua] tries to take an intuitive view (rather than a mathematical view) of working in the frequency domain, and trying to figure out how to “get” what OFDM is (and why it’s so important). [Joshua] sent his talk in to us in the hope that it would be useful for all skill levels, both folks who are new to radio and signal processing, and folks who are well experienced in working in the frequency domain.

If you think you’ve seen “The Unreasonable Effectiveness of $TOPIC” before, that’s because hacker’s can’t help but riff on the original The Unreasonable Effectiveness of Mathematics in the Natural Sciences, wherein a scientist wonders why it is that mathematical methods work at all. They seem to, but how? Or why? Will they always continue to work? It’s a mystery.

Hidden away in the notes and at the end of his presentation, [Joshua] notes that every year he watches The Fast Fourier Transform (FFT): Most Ingenious Algorithm Ever? and every year he understands a little more.

If you’re interested in OFDM be sure to check out AI Listens To Radio.

Continue reading “The Unreasonable Effectiveness Of The Fourier Transform” →

DIY Grid Dip Meter Teardown

January 7, 2026 by Al Williams 5 Comments

You don’t see them much anymore, but there was a time when any hobbyist who dealt with RF probably had a grid dip meter. The idea was to have an oscillator and measure the grid current as it coupled to external circuits. At resonance, the grid current would go down or dip, hence the name. In the hands of someone who knew how to use it, the meter could measure inductance, capacitance, tuned circuits, antennas, and more. [Thomas] takes a peek inside a homebrew unit from the 1950s in a recent video you can see below.

These meters often have a few things in common. They usually have a plug-in coil near the top and a big tuning capacitor. Of course, there’s also a meter. You have to pick the right coil for the frequency of interest, which both sets the oscillator frequency range and couples to the circuit under test.

Continue reading “DIY Grid Dip Meter Teardown” →

An RP2040 Powered ADS-B Receiver

January 7, 2026 by Fenix Guthrie 34 Comments

If you’ve ever heard the sound of an aircraft passing overhead and looked at an online plane tracker to try and figure out what it was, then you’ve interacted with ADS-B. It’s a protocol designed to enable easier aircraft monitoring, and it just so happens you can decode it yourself with the right hardware and software — which is how [John McNelly] came to develop ADSBee, an open source ADS-B receiver based around an RP2040.

ADS-B uses on–off keying (OOK) at 1 Mbps, and operates at 1090 MHz. This might seem like a rather difficult protocol to decode on a microcontroller, but the RP2040’s PIO is up to the task. All it takes is a bit of optimization, and a some basic RF components to amplify and digitize the signals.

However, not all aircraft utilize the 1090 MHz ADS-B implementation, and instead use a related protocol called UAT. Operating at 978 MHz, a second receiver is needed for decoding UAT traffic data, which is where the CC1312 comes into play. ADSBee may even be the first open source implementation of a UAT decoder!

What’s quite impressive is the various form factors the module is available in. Ranging from small solder-down modules to weatherproof outdoor base stations, nearly every potential need for an ADS-B receiver is covered. With POE or ESP32 S3 options available, there is no shortage of networking options either!

ADSBees have been placed in numerous locations, ranging from base stations to drones. One user even built out a tiny flight display cluster complete with traffic indicators into an FPV drone.

This isn’t the first time we have seen ADS-B receivers used by drone enthusiasts, but this is certainly the most feature rich and complete receiver we have come across.

The Cutting Truth About Variable Capacitors

January 1, 2026 by Al Williams 10 Comments

If you’ve seen a big air-variable capacitor, you may have noticed that some of the plates may have slots cut into them. Why? [Mr Carlson] has the answer in the video below. The short answer: you can bend the tabs formed by the slots to increase or decrease the capacitance by tiny amounts for the purpose of tuning.

For example, if you have a radio receiver with a dial, you can adjust the capacitor to make certain spots on the dial have an exact frequency. Obviously, you can only adjust in bands depending on how many slots are in the capacitor. Sometimes the adjustments aren’t setting the oscillator’s frequency. For example, the Delco radio he shows uses the capacitor to peak the tuning at the specified frequency.

You usually only find the slots on the end plates and, as you can see in the video, not all capacitors have the slots. Of course, bending the plates with or without slots will make things change. Just don’t bend enough to short to an adjacent plate or the fixed plates when the capacitor meshes.

Of course, not all variable capacitors have this same design. We’ve seen a lot of strange set ups.

Continue reading “The Cutting Truth About Variable Capacitors” →

Bringing A Yagi Antenna To 915MHz LoRa

December 31, 2025 by Tyler August 34 Comments

If you’re a regular reader of Hackaday, you may have noticed a certain fondness for Meshtastic devices, and the LoRa protocol more generally. LoRa is a great, low-power radio communications standards, but sometimes the antennas you get with the modules can leave you wanting more. That’s why [Chris Prioli] at the Gloucester County Amateur Radio Club in the great state of New Jersey have got a Yagi antenna for North America’s 915 MHz LoRa band.

Right out the gate, their article links to one of ours, where [tastes_the_code] builds a Yagi antenna for the European 868 MHz LoRa. Like [tastes_the_code], the radio club found [Chris]’s antenna gives much better reception than what came with the LoRa module. Looking out their window, instead of two Metastatic nodes with a stock antenna, one club member is now connecting to two hundred.

A simulation of the radiation pattern. Looks like a Yagi, alright.

Now, the Yagi is directional, so you only get that boost pointed down the axis of the antenna, but at least in simulation they estimate a 7.7 dB front-to-back gain vs under 3 dB for an omnidirectional antenna. Not bad, for a simple 3D print and some stiff wire!

If you don’t want to re-invent the wheel again, check out the GCARC’s GitHub for files if you’re in North America. If you’re in Europe, check out [taste_the_code]’s build from last year. Of course whatever band you’re operating in, Yagi isn’t your only roll-your-own option for a LoRa antenna.

Thanks to [Jon Pearce WB2MNF] for the tip!

Lessons Learned After Trying MeshCore For Off-grid Text Messaging

December 6, 2025 by Donald Papp 67 Comments

[Michael Lynch] recently decided to delve into the world of off-grid, decentralized communications with MeshCore, because being able to communicate wirelessly with others in a way that does not depend on traditional communication infrastructure is pretty compelling. After getting his hands on a variety of hardware and trying things out, he wrote up his thoughts from the perspective of a hardware-curious software developer.

He ends up testing a variety of things: MeshCore firmware installed on a Heltec V3 board (used via an app over Bluetooth), a similar standalone device with antenna and battery built in (SenseCAP T-1000e, left in the header image), and a Lilygo T-Deck+ (right in the header image above). These all use MeshCore, which is built on and reportedly compatible with Meshtastic, a framework we have featured in the past.

Continue reading “Lessons Learned After Trying MeshCore For Off-grid Text Messaging” →