LoRa Repeater Lasts 5 Years On PVC Pipe And D Cells

December 2, 2025 by Donald Papp 64 Comments

Sometimes it makes sense to go with plain old batteries and off-the-shelf PVC pipe. That’s the thinking behind [Bertrand Selva]’s clever LoRaTube project.

PVC pipe houses a self-contained LoRa repeater, complete with a big stack of D-size alkaline cells.

LoRa is a fantastic solution for long-range and low-power wireless communication (and popular, judging by the number of projects built around it) and LoRaTube provides an autonomous repeater, contained entirely in a length of PVC pipe. Out the top comes the antenna and inside is all the necessary hardware, along with a stack of good old D-sized alkaline cells feeding a supercap-buffered power supply of his own design. It’s weatherproof, inexpensive, self-contained, and thanks to extremely low standby current should last a good five years by [Bertrand]’s reckoning.

One can make a quick LoRa repeater in about an hour but while the core hardware can be inexpensive, supporting electronics and components (not to mention enclosure) for off-grid deployment can quickly add significant cost. Solar panels, charge controllers, and a rechargeable power supply also add potential points of failure. Sometimes it makes more sense to go cheap, simple, and rugged. Eighteen D-sized alkaline cells stacked in a PVC tube is as rugged as it is affordable, especially if one gets several years’ worth of operation out of it.

You can watch [Bertrand] raise a LoRaTube repeater and do a range test in the video (French), embedded below. Source code and CAD files are on the project page. Black outdoor helper cat not included.

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All Handheld Antennas Are Not Born The Same

November 30, 2025 by Jenny List 15 Comments

If you own a handheld transceiver of any type then the chances are it will come with a “rubber duck” style antenna. These flexible rubber-coated antennas are a compromise in performance, being significantly smaller than a wavelength at their frequency of operation. [OM40ET] has an interesting video in which he investigates this by tearing down a cheap rubber duck antenna and an even cheaper fake.

These antennas usually have a flexible upper section and a bulge at the bottom over the connector. The fake one has nothing in the bulge except the antenna wire and thus has a very high SWR, while the “real” one has a loading coil. This coil is an interesting design, because it’s designed such that the antenna has two resonant points at the 2 metre and 70 centimetre amateur bands. On paper it’s a tapped coil fed at the tap through a capacitor for matching, but a more detailed appraisal will tell you that the two halves of the coil are designed to return those two resonances. It’s still a not-very-good antenna, but the fact that it works at all is something.

If you want something better at VHF and haven’t got much space, all is not lost. We recently featured a VHF magnetic loop.

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Building A Low-Cost Satellite Tracker

November 26, 2025 by Bryan Cockfield 8 Comments

Looking up at the sky just after sunset or just before sunrise will reveal a fairly staggering amount of satellites orbiting overhead, from tiny cubesats to the International Space Station. Of course these satellites are always around, and even though you’ll need specific conditions to view them with the naked eye, with the right radio antenna and only a few dollars in electronics you can see exactly which ones are flying by at any time.

[Josh] aka [Ham Radio Crash Course] is demonstrating this build on his channel and showing every step needed to get something like this working. The first part is finding the correct LoRa module, which will be the bulk of the cost of this project. Unlike those used for most Meshtastic nodes, this one needs to be built for the 433 MHz band. The software running on this module is from TinyGS, which we have featured here before, and which allows a quick and easy setup to listen in to these types of satellites. This build goes much further into detail on building the antenna, though, and also covers some other ancillary tasks like mounting it somewhere outdoors.

With all of that out of the way, though, the setup is able to track hundreds of satellites on very little hardware, as well as display information about each of them. We’d always favor a build that lets us gather data like this directly over using something like a satellite tracking app, although those do have their place. And of course, with slightly more compute and a more directed antenna there is all kinds of other data beaming down that we can listen in on as well, although that’s not always the intent.

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Assistive Radio Tells You What You Can’t See

November 22, 2025 by Al Williams 2 Comments

We think of radios as audio devices, but for people who are visually impaired, it can be difficult to tell which channel you are listening to at any given time. [Sncarter] has a family member with vision impairment and built a radio to help her. Unfortunately, it was difficult to replicate, so he decided to try again. The result is an FM radio that provides audible status notifications about power and frequency. Check it out in the video below.

This isn’t just some hacked-up commercial radio, but a ground-up design that uses a TEA5767 with an ATMega328 for control. There is an LCD for when someone else might use the radio and an audio amplifier. He built the prototype on a breadboard, but moved the finished product to a PCB.

It isn’t just the electronics and the sound that are assistive. The case has raised bosses to help the user find things like the switch and rotary encoder. The Arduino can speak frequency announcements, although the quality of the voice is something he wants to tackle in the next revision.

These radios on a chip give you many design options. These same ideas can be useful for audiobook players, too.

Gilbert Cell Lacks Sullivan

November 20, 2025 by Al Williams 7 Comments

If you’ve ever used an NE602 or similar IC to build a radio, you might have noticed that the datasheet has a “gilbert cell” mixer. What is that? [Electronics for the Inquisitive Experimenter] explains them in a recent video. The gilbert cell is a multiplier, and multiplying two waveforms will work to mix them together.

At the heart of the gilbert cell is essentially three differential amplifiers that share a common current source. The video shows LTSpice simulations of the circuits as he explains them.

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Cheap VHF Antenna? Can Do!

November 18, 2025 by Jenny List 6 Comments

The magnetic loop antenna is a familiar sight in radio amateur circles as a means to pack a high performance HF antenna into a small space. It takes the form of a large single-turn coil made into a tuned circuit with a variable capacitor, and it provides the benefits of good directionality and narrow bandwidth at the cost of some scary RF voltages and the need for constant retuning. As [VK3YE] shows us though, magnetic loops are not limited to HF — he’s made a compact VHF magnetic loop using a tin can.

It’s a pretty simple design; a section from the can it cut out and made into a C shape, with a small variable capacitor at the gap. The feed comes in at the bottom, with the feed point about 20 % of the way round the loop for matching. The bandwidth is about 100 MHz starting from the bottom of the FM broadcast band, and he shows us it receiving broadcast, Airband, and 2 meter signals. It can be used for transmitting too and we see it on 2 meter WSPR, but we would have to wonder whether the voltages induced by higher power levels might be a little much for that small capacitor.

He’s at pains to point out that there are many better VHF antennas as this one has no gain to speak of, but we can see a place for it. It’s tiny, if you’re prepared to fiddle with the tuning its high Q gets rid of interference, and its strong side null means it can also reduce unwanted signals on the same frequency. We rather like it, and we hope you will too after watching the video below.

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2025 Component Abuse Challenge: A Piezo Disk Powers A Transmitter

November 2, 2025 by Jenny List 12 Comments

A piezo disk transducer is a handy part for reproducing beeps and boops, and can also function as a rudimentary microphone. Being a piezoelectric element, it can also generate usable power. Enough to run a radio transmitter? [b.kainka] is here to find out, with what may be the simplest possible transmitter circuit.

The active element in the circuit, such as it is, comes from a crystal. This functions as an extremely stable and high Q tuned circuit. When excited by a pulse of electricity, the circuit will carry oscillations in a similar manner to a bell ringing until the pulse is exhausted. A small lever fashioned from a piece of wire supplies the voltage by flexing the piezo disk and a contact, a diode discharges the reverse voltage as the disk returns to shape, and a small capacitor provides an AC path to ground. It works, if a small pulse of very low-power RF near the crystal’s frequency can be described as working.

It may not be the most practical transmitter, but it’s certainly something we’ve not seen before. It’s part of our 2025 Component Abuse Challenge, for which you still have time to make an entry yourself if you have one.