Radio Hacks

1355 Articles

Ham Almost Cooks ‘Dog

June 14, 2023 by 34 Comments

For those of us licensed in other countries it comes as something of a surprise to find that American radio amateurs now have to run RF exposure calculations as part of their licence requirements. [Ham Radio Crash Course] as approached this in a unique fashion, by running around 800 watts of 6-metre power into a vertical antenna festooned with hotdogs. That’s right, this ham is trying to cook some ‘dawgs! Is his station producing dangerous levels of power that might cook passers-by?

Of course, aside from a barely-warmed line along where the ‘dogs were attached to the antenna there’s no heating to be found. But we think he’s trying to make the point in the video below the break about the relative pointlessness of applying RF field limits which are definitely relevant at much higher frequencies, to hams at low frequencies.

It leaves us curious as to how that 800 watts could be efficiently transferred into the sausages and really cook them. Strapping them to a vertical is we think the equivalent of strapping anything resistive to a conductor, they do not form a significant  enough part of the circuit. We think that even six metres could cook a sausage if it could be efficiently coupled into it, so we’d suggest putting a grounded sausage up the middle of a close-wound helix.

If you have any thoughts on the RF exposure calculations, or on the best way to cook a ‘dog with 6m, we’d love to hear the, in the comments. Meanwhile, this isn’t the first piece of ‘dog-based shenanigans we’ve brought you.

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Passionate Hams Make Their Mark On The Hack Chat

June 12, 2023 by 63 Comments

Let’s be honest — there are some not very pleasant stereotypes associated with amateur radio, at least if you ask outsiders. Hams are often thought of as being in two camps: old guys who can’t figure out modern technology or conspiracy theorists who think their knowledge of radio will give them an edge after the world becomes a post-apocalyptic hellscape. We’ll leave it to you to decide which is the worse brush to be painted with.

As is often the case, the best way to fight such ignorance is with education and outreach. Events like our weekly Hack Chat are a perfect platform for that, as it allows the curious to ask questions and get answers directly from subject matter experts. This is precisely why we invited Mark Hughes and Beau Ambur to helm last week’s Chat. The fact that they’re both relatively recent licensees makes them uniquely qualified to shed some light on what it’s like to become part of the ham radio community in the 21st century. As an added bonus, they’re both sharp and articulate technologists — about as far as you can get from the mental image of the doddering old granddad who prefers the simplicity of the Morse key to those newfangled smarty-phones.

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Listening To The ISS On The Cheap

June 10, 2023 by 36 Comments

Like any hobby, amateur radio has no upper bounds on what you can spend getting geared up. Shacks worth tens of thousands of dollars are easy to come by, and we’ll venture a guess that there are hams out there pushing six figures with their investment in equipment. But hands down, the most expensive amateur radio station ever has to be the one aboard the  International Space Station.

So what do you need to talk to a $100 billion space station? As it turns out, about $60 worth of stuff will do, as [saveitforparts] shows us in the video below. The cross-band repeater on the ISS transmits in the 70-cm ham band, meaning all that’s needed to listen in on the proceedings is a simple “handy talkie” transceiver like the $25-ish Baofeng shown. Tuning it to the 437.800-MHz downlink frequency with even a simple whip antenna should get you some reception when the ISS passes over.

In our experience, the stock Baofeng antenna isn’t up to the job, so something better like the Nagoya shown in the video is needed. Better still is a three-element Yagi tuned down slightly with the help of a NanoVNA; coupled with data on when the ISS will be within line-of-sight, picking up the near-constant stream of retransmissions from the station as Earth-based hams work it should be a snap — even though [saveitforparts] only listened to the downlink frequency here, for just a bit more of an investment it’s also possible for licensed hams to uplink to the ISS on 145.900 MHz.

For those who want a slightly higher level of difficulty, [saveitforparts] also has some tips on automating tracking with an old motorized mount for CCTV cameras. Pitchfork notwithstanding, it’s not the best antenna tracker, but it has promise, and we’re eager to see how it pans out — sorry. But in general, the barrier to entry for getting into space communications is so low that you could easily make this a weekend project. We’ve been discussing this and other projects on the new #ham-shack channel over on the Hackaday Discord. You should pop over there and check it out — we’d be happy to see you there.

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Radio Apocalypse: Hardening AM Radio Against Disasters

June 6, 2023 by 64 Comments

If you’ve been car shopping lately, or even if you’ve just been paying attention to the news, you’ll probably be at least somewhat familiar with the kerfuffle over AM radio. The idea is that in these days of podcasts and streaming music, plain-old amplitude modulated radio is becoming increasingly irrelevant as a medium of mass communication, to the point that automakers are dropping support for it from their infotainment systems.

The threat of federal legislation seems to have tapped the brakes on the anti-AM bandwagon, at least for now. One can debate the pros and cons, but the most interesting tidbit to fall out of this whole thing is one of the strongest arguments for keeping the ability to receive AM in cars: emergency communications. It turns out that about 75 stations, most of them in the AM band, cover about 90% of the US population. This makes AM such a vital tool during times of emergency that the federal government has embarked on a serious program to ensure its survivability in the face of disaster.

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Nice Try, But It’s Not Aperture Synthesis

May 26, 2023 by 17 Comments

Some of the world’s largest radio telescopes are not in fact as physically large as they claim to be, but instead are a group of telescopes spread over a wide area whose outputs are combined to produce a virtual telescope equal in size to the maximum distance between the constituents of the array. Can this be done on the cheap with an array of satellite dishes? It’s possible, but as [saveitforparts] found out when combining a set of Tailgater portable dishes, not simply by linking together the outputs from a bunch of LNBs.

The video below the break still makes for an interesting investigation and the Tailgater units are particularly neat. It prompted us to read up a little on real aperture synthesis, which requires some clever maths and phase measurement for each antenna. Given four somewhat more fancy LNBs with phase-locked local oscillators and an software-defined radio (SDR) for each one then he might be on to something.

If you’re curious about the cyberdeck in the video, you might like to read our coverage of it. And the Tailgater might be a bit small, but you can still make a useful radio telescope from satellite TV parts.

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Spy Transceiver Makes Two Tubes Do The Work Of Five

May 19, 2023 by 26 Comments

Here at Hackaday, we love following along with projects as they progress. That’s especially true when a project makes a considerable leap in terms of functionality from one version to another, or when the original design gets more elegant. And when you get both improved function and decreased complexity at the same time? That’s the good stuff.

Take the recent improvements to a vacuum tube “spy radio” as an example. Previously, [Helge (LA6NCA)] built both a two-tube transmitter and a three-tube receiver, either of which would fit in the palm of your hand. A little higher math seems to indicate that combining these two circuits into a transceiver would require five tubes, but that’s not how hams like [Helge] roll. His 80-m CW-only transceiver design uses only two tubes and a lot of tricks, which we admit we’re still wrapping our heads around. On the receive side, one tube serves as a mixer/oscillator, combining the received signal with a slightly offset crystal-controlled signal to provide the needed beat frequency. The second tube serves as the amplifier, both for the RF signal when transmitting, and for audio when receiving.

The really clever part of this build is that [Helge] somehow stuffed four separate relays into the tiny Altoids tin chassis. Three of them are used to switch between receive and transmit, while the fourth is set up as a simple electromagnetic buzzer. This provides the sidetone needed to effectively transmit Morse code, and is about the simplest way we’ve ever seen to address that need. Also impressive is how [Helge] went from a relatively expansive breadboard prototype to a much more compact final design, and how the solder was barely cooled before he managed to make a contact over 200 km. The video below has all the details.

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Cornering The Antenna Market

May 17, 2023 by 21 Comments

Sometimes antennas can seem like black magic. However, when you see things like a dish antenna, it sort of makes sense, right? Just like a mirror focuses light, the parabola of a dish focuses RF energy. But [IMSAI Guy] shows another common-sense antenna arrangement: a corner reflector dipole. He had built one years ago and decided to do a bit of research and make another one.

In a clever use of copper-clad board, he was able to make a reasonable reflector by soldering together three boards and an RF connector. A single wire makes the “driven element,” and by bending it to just the right position, you can change the characteristic impedance for matching.

The antenna, in this case, is essentially a quarter-wave antenna with a ground plane and reflector arrangement. After the obligatory chalk talk, he breaks out the vector network analyzer and shows how well it matches. He didn’t, however, measure the gain or directional selectivity due to the reflector.

Intuitively, you’d think this kind of antenna would be good for direction finding purposes. In fact, hams that use handy talkies for direction finding often use their bodies to block signals, much like these reflectors should.

The [IMSAI Guy] reflector is pretty small, but you can easily make bigger ones. Using PCB material for antennas isn’t anything new, either, but we still enjoyed this simple corner reflector build.

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