A Variable Capacitor For Not A Lot

March 7, 2022 by Jenny List 35 Comments

There’s one component which used to be ubiquitous in every experimenter’s junk box, but nowadays unless you happen to be a radio amateur the chances are you may not have seen one in a long time, if ever. We’re talking of course about the air-dielectric variable capacitor, the tuning element for millions of radio receivers back in the day but now long ago replaced by much flimsier polymer-dielectric parts. There’s still a need for variable capacitors though, in particular a high-voltage variant for use in magnetic loop antennas. It’s something that [Ben] had a need for, which he solved with a clever combination of PCB material and 3D printing.

While the variable capacitors of yore invariably used intersecting vanes on a rotor, this one has two large parallel plates that intersect as one is moved over the other with a lead screw. It’s cheap and effective, and best of all, the files to make it can be downloaded from Thingiverse. He claims a 34pF-164pF capacitance range, which, looking at the size of the plates we find to be believable (and which is a useful range for most HF applications). We like this solution, and believe it makes more sense than being scalped for an older example at a radio rally.

This isn’t the first variable capacitor we’ve shown you, though some previous examples have been more conventional.

Retro And New Tech Combine In This Hybrid Ham Transmitter

February 27, 2022 by Dan Maloney 9 Comments

We’ve said it before and we’ll say it again: the best part about holding an amateur radio license is that it lets you build and use your own transmitting equipment. Hams have been doing this for more than a century — indeed, it was once the only way to get on the air — using whatever technology was available. But the mix of technologies in this low-power transmitter for the 80-meter band is something you don’t see every day.

As ham [Helge Fykse (LA6NCA)] describes in the video below, the project began when he came into possession of a bonanza of vacuum tubes — 12A6 tetrodes, specifically. The new-old-stock tubes were perfect for an RF power amplifier, but that left the problem of what to use for an oscillator. [Helge] chose to meld the old with the new and used oscillator board that he designed. The board has an ATmega88 microcontroller and an Si5351 oscillator, along with a 3V3 regulator to let the module run on 12 volts. And for a nice retro touch, [Helge] put the board in a 3D printed case that looks like an old-fashioned quartz crystal.

There are some other nice design touches here too. A low-pass filter cleans up the harmonics of the oscillator’s 3.5-MHz square wave output before feeding it to the amplifier, in a nod to proper spectrum hygiene. The primary for the amp’s air-core output transformer is hand-wound, with 3D printed spacers to keep the winding neat and even. The tuning process shown below is interesting, and the transmitter was used to make a solid contact with another ham about 100 km away. And we really liked the look of [Helge]’s shack, stuffed as it is with gear both old and new.

We’ve personally tried the Si5351 for QRP transmitters before, but this blend of the old and new really makes us want to find some tubes and get to playing.

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Machining Waveguides For 122 GHz Operation Is Delicate Work

February 12, 2022 by Lewin Day 21 Comments

Millimeter-wave Radars used in modern cars for cruise control and collision avoidance are usually designed to work at ranges on the order of 100 meters or so. With some engineering nous, however, experimenters have gotten these devices sending signals over ranges of up to 60 km in some tests. [Machining and Microwaves] decided to see if he could push the boat out even further, and set out machining some waveguide combiner cavities so he could use the radar chips with some very high-performance antennas.

Precision-machined components are required to successfully use these 122 GHz components for long-range transmissions.

The end goal of the project is to produce a 53 dBi antenna for the 122GHz signal put out by the mmWave radar chips commonly found in automotive applications. Working at this frequency requires getting tolerances just so in order to create an antenna that performs well.

Plenty of fine lathe work and cheerful machining banter later, and the precision waveguide is done. It may not look like much to the untrained eye, but much careful design and machining went on to make it both easy to attach to the radar and parabolic antenna system, and to make it perform at a high enough level to hopefully break records set by other enterprising radio experimenters. If that wasn’t all hard enough, though, the final job involved making 24 of these things!

There aren’t a whole lot of microwave antenna-specific machining channels on YouTube, so if you’ve been thirsty for that kind of content, this video is very much for you. If you’re more interested in antennas for lower frequencies, though, you might find some of our other stories to your liking. Video after the break.

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Directional Antenna 3-Way

January 21, 2022 by Al Williams 10 Comments

If you read old antenna books, you’ll probably see the idea of phased vertical antennas. These use certain lengths of coax to control the phase of a signal going to three verticals in a triangular configuration. Depending on the phasing, you can cause the array of antennas to be directional in one of three directions. [DX Commander] designed a very modern version of this antenna and shows the theory behind it in a recent video that you can see below.

It seems another ham built the antenna and a control box for it which he’s sent to [DX Commander] although he hasn’t set it up yet to create an 80 meter directional antenna. We’ll be interested in seeing how it works in practice.

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Modern Features In Classic Radio

December 7, 2021 by Bryan Cockfield 53 Comments

As consumer electronics companies chase profits on tighter and tighter margins, it seems like quality is continually harder to find for most average consumer-grade products. Luckily, we don’t have to hunt through product reviews to find well-built merchandise since we have the benefit of survivorship bias to help us identify quality products from the past that have already withstood the test of time. [Tom] has forever been fond of this particular Sony TV/radio combo from the ’70s so he finally found one and set about modernizing it in a few key ways.

Among the modifications to this 1978 Sony FX-300 include the addition of a modern color display, Bluetooth, an upgraded FM radio, and a microphone. At the center of all of this new hardware is a Teensy 4 which [Tom] has found to be quite powerful and has enough capabilities to process the audio that’s being played in order to make visual representations of the sound on the screen. He also implemented a bitcrusher filter and integrated it into the controls on the original hardware. He’s using an optimized version of this library to cram all of that processing ability into such a small chip, and the integration of all this new hardware is so polished that it looks like it could be an original Sony stereo from the modern era.

While some may complain about restomod-type builds like this, we don’t really see any need to be arbitrarily or absolutely faithful to bygone eras even if the original hardware was working properly in the first place. What works is taking the proven technology of the past and augmenting it with modern features to enjoy the best of both worlds. Much like this hi-fi stereo which blends the styles and technology of the 90s with that of the 60s in an equally impressive way.

Is The Game Up For Baofeng In Europe?

December 5, 2021 by Jenny List 121 Comments

For radio enthusiasts worldwide, the inexpensive Chinese handheld radios produced by the likes of Baofeng and other brands have been a welcome addition to their arsenal. They make an ideal first transceiver for a new licensee, a handy portable for any radio amateur, and an inexpensive basis for UHF or VHF experimentation. Unfortunately with the low cost comes something of a reputation for not having the cleanest spectral output, and it seems that this has caught the attention of regulators in Germany and Poland. In Germany this has resulted in the announcement of a sales prohibition (PDF in German) which seems likely to be repeated across the rest of the EU.

It seems what has happened is that the quality of the Baofeng radios on sale doesn’t match that claimed in their conformity documents, which should honestly come as a surprise to nobody. It is interesting that the paperwork mentions the Baofeng UV-5R specifically, as it seems likely to us that an inevitable game of whack-a-mole will ensue with the same radios appearing under ever more brand names and part numbers. The basic UV-5R already appears under a number of variants, for example the one where this is being written is a near-identical but slightly more powerful BF-F8, so this should again come as no surprise.

If you live in Europe should you panic buy a Baofeng while you still can? Probably not, unless you really need one. Something tells us they will remain readily available from the usual overseas sources for years to come. Meanwhile this isn’t the first time a regulator has raised questions about this type of radio.

Thanks [2ftg] for the tip.

Header image: Варвара Каминская, CC BY-SA 4.0.

Two Mars Orbiters Chatted For Atmospheric Science

December 2, 2021 by Roger Cheng 9 Comments

Mission extensions for interplanetary robot explorers are usually continuations of their primary mission. But sometimes the hardware already on board are put to novel uses. European Space Agency has started using radio equipment on board two Mars orbiters to probe the Martian atmosphere.

The scientific basis is straightforward: radio signals are affected by whatever they had traveled through. When transmitting data, such effects are noises to be minimized. But we can also leverage it for atmospheric science here on Earth. ESA applied the same concept at Mars: by transmitting a known signal from one Mars orbiter to another, changes in the received signal tells scientists something about the Martian atmosphere between them.

So the theory sounds good, but the engineering implementation took some work. Most radio equipment on board ESA’s orbiters were not designed to talk to each other. In fact they were deliberately different to minimize interference. However, both Mars Express and Trace Gas Orbiter were designed to act as data relays for surface probes, and not just the one they each carried to Mars. Thus their related radio gear were flexible enough to be adapted to this experiment.

These two machines launched over a decade apart. Yet they could now communicate with each other in Mars orbit using radios originally designed for talking to the surface. In the near future such chatter will probably be limited, as Trace Gas Orbiter is still in the middle of its primary mission. But this success lets ESA think about how much further to push the idea in the future. In the meantime Mars Express will continue its observation of Mars, doing things like giving us context on Perseverance rover landing.