Radio Hacks

1403 Articles

FM Transmitter Remotely Controlled Via ESP32

October 18, 2024 by 14 Comments

Imagine you’ve got an FM transmitter located some place. Wouldn’t it be mighty convenient if you could control that transmitter remotely? That way, you wouldn’t have to physically attend to it every time you had to change some minor parameters! To that end, [Ricardo Lima Caratti] built a rig to do just that.

The build is based around the QN8066—a digital FM transceiver built into a single chip. It’s capable of transmitting and receiving anywhere from 60 MHz to 108 MHz, covering pretty much all global FM stereo radio bands. [Ricardo] paired this chip with an ESP32 for command and control. The ESP32 hosts an HTTP server, allowing the administration of the FM transmitter via a web browser. Parameters like the frequency, audio transmission mode, and Radio Data Service (RDS) information can be controlled in this manner.

It’s a pretty neat little build, and [Ricardo] demonstrates it on video with the radio transmitting some field day content. We’ve seen some other nifty FM transmitters over the years, too. Video after the break.

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Tiny LoRa GPS Node Relies On ESP32

October 17, 2024 by 10 Comments

Sometimes you need to create a satellite navigation tracking device that communicates via a low-power mesh network. [Powerfeatherdev] was in just that situation, and they whipped up a particularly compact solution to do the job.

As you might have guessed based on the name of its creator, this build is based around the ESP32-S3 PowerFeather board. The PowerFeather has the benefit of robust power management features, which makes it perfect for a power-sipping project that’s intended to run for a long time. It can even run on solar power and manage battery levels if so desired. The GPS and LoRa gear is all mounted on a secondary “wing” PCB that slots directly on to the PowerFeather like a Arduino shield or Raspberry Pi HAT. The whole assembly is barely larger than a AA battery.

It’s basically a super-small GPS tracker that transmits over LoRa, while being optimized for maximum run time on limited power from a small lithium-ion cell. If you’re needing to do some long-duration, low-power tracking task for a project, this might be right up your alley.

LoRa is a useful technology for radio communications, as we’ve been saying for some time. Meanwhile, if you’ve got your own nifty radio comms build, or anything in that general milleu, don’t hesitate to drop us a line!

A Phone? A Ham Radio? Relax! It’s Both!

October 15, 2024 by 23 Comments

A lot of hams like to carry a VHF radio. Of course, nearly everyone wants to carry a phone. Now, thanks to the kv4p HT, you don’t have to carry both. The open-source device connects to your Android smartphone and turns it into a radio transceiver. You can build it yourself for about $35. Check out the video below.

The device uses an ESP32 and only transmits one watt, but it has lots of features like APRS and scanning.

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What’s Your SWR? Are You Sure?

October 12, 2024 by 11 Comments

If you are involved in any sort of radio transmission, you probably have at least heard of SWR or standing wave ratio. Most transmitters can measure it these days and most ham radio operators have tuners that measure it, also. But what are you measuring? [KI8R] points out that if your coax has loss — and what coax doesn’t? — you are probably getting an artificially low reading by measuring at the transmitter.

The reason is that most common SWR-measuring instruments pick up voltage. If you measure, for example, 10V going out and 1V going back, you’d assume some SWR from that. But suppose your coax loses half the voltage (just to make an obvious example; if your coax loses half the voltage, you need new coax).

Now, you really have 5V getting to your antenna, and it returns 2V. The loss will affect the return voltage just like the forward voltage. Reflecting 2V from 5 is a very different proposition from reflecting 1V out of 10!

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Braun TS2 Radio Turns 68, Gets Makeover

October 9, 2024 by 7 Comments

The Braun TS2 radio was a state-of-the art tube set in 1956. Today it still looks great, but unsurprisingly, the one that [Manuel Caldeier] has needed a little tender loving care. The table radio had a distinct style for its day and push-buttons. However, the dial glass and the speaker grill needed replacement. Even more interesting, the radio has a troublesome selenium rectifier, giving him the perfect chance to try out his new selenium rectifier solid-state replacement.

The radio is as good-looking inside as it is outside. You can tell that this isn’t his first restoration, as he has several tricks to test things at different stages of the project.

While the radio looked good, it smelled of smoke, which required a big effort to clean. The dial glass was intact enough for him to duplicate it in a graphic program and print it on a transparent adhesive sticker. With a deep breath, he removed the original markings from the glass so he could add the sticker to it. That didn’t work because the label needed cutouts. So now he is waiting for a piece of acrylic that will have the art UV printed on it.

We want to see the next part as we imagine the radio sounds as good as it looks when it is working. If you want to know more about the rectifier replacement, we covered that earlier. Even years later, Braun would have a clean aesthetic.

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A Universal RF Amplifier

September 26, 2024 by 17 Comments

If you need an amplifier, [Hans Rosenberg] has some advice. Don’t design your own; grab cheap and tiny RF amplifier modules and put them on a PCB that fits your needs. These are the grandchildren of the old mini circuits modules that were popular among hams and RF experimenters decades ago. However, these are cheap, simple, and tiny.

You only need a handful of components to make them work, and [Hans] shows you how to make the selection and what you need to think about when laying out the PC board. Check out the video below for a very detailed deep dive.

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Replacing Selenium Rectifiers

September 24, 2024 by 14 Comments

Old radios often had selenium rectifiers to convert AC to DC. The problem is that the old units, dating back to 1933, are prone to failure and to release dangerous chemicals like hydrogen selenide. [M Caldeira] has a new board made to fit a particular rectifier and also allows a varying voltage drop. The circuit consists of a few diodes, a MOSFET, and a pot for adjusting the voltage drop. An IRF840 MOSFET provides the adjustment.

Did it work? It did. The good news is that if it fails — which shouldn’t happen very often — it won’t release stinky and noxious fumes

We wondered if he should 3D print a fake case to make it look more the part. If you haven’t seen a real selenium rectifier, they were made of stacks of metal plates coated with bismuth or nickel. Then, a film of doped selenium was annealed to the surface to form cadmium selenide. Each plate could handle about 20 V and the more plates you used, the more reverse voltage the device could withstand.

Selenium was also found in old photocells. If you fancy replacing other parts of an old radio, you might consider a faux magic eye or even one of the main tubes.

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