GNU Radio Decodes Voyager Data

With the 44th anniversary of the launch of Voyager I, [Daniel] decided to use GNU Radio to decode Voyager data. The data isn’t live, but a recording from the Green Bank Telescope. The 16 GB file is in GUPPI format which stores raw IQ samples.

The file contains 64 frequency channels of just under 3MHz each. The signal of interest is in one channel, so it is easy to just throw away the rest of the data.

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Building A Hundred-Year-Old Radio Transmitter

Our Hackaday team is spread across the world, but remains in easy contact through the magic of the Internet. A number of us hold amateur radio callsigns, so could with a bit of effort and expenditure do the same over the airwaves. A hundred years ago this would have seemed barely conceivable as amateurs were restricted to the then-considered-unusable HF frequencies.

Thus it was that in December 1921 a group of American radio amateurs gathered in a field in Greenwich Connecticut in an attempt to span the Atlantic. Their 1.3 MHz transmitter using the callsign 1BCG seems quaintly low-frequency a hundred years later, but their achievement of securing reception in Ardrossan, Scotland, proved that intercontinental communication on higher frequencies was a practical proposition. A century later a group from the Antique Wireless Association are bringing a replica transmitter to life to recreate the event.

A free-running oscillator is today rarely seen in a radio transmitter, but at the time their single-tube Colpitts oscillator using a UV-204 transmitting tube would have been considered a stable source. That fed a 1KW power amplifier using three more UV-204s in parallel, which in turn fed a Marconi-style T antenna design with an earth counterpoise of multiple radial wires. The replica was originally built for an event in 1996, and substitutes the similar 204A tube for the now unobtainable UV-204. Even then, hundred-year-old tubes are hard to find in 2021, so they could only muster a single working example for the PA.

All in all it’s a very interesting project, and one of which we hope we’ll hear more as the anniversary approaches. If we can get the transmission details we’ll share them with you, and let’s see whether the same distances can be traversed with the more noisy conditions here in 2021.

To demonstrate how advanced this transmitter was for 1921, take a look at the Alexanderson alternator, its mechanical contemporary.

The Curious Case Of The Radio Amateur And The Insulin Pump

A substantial part of gaining and holding an amateur radio licence relates to the prevention of radio interference. In days past this meant interference to analogue television broadcasts, but with ever more complex devices becoming commonplace in homes it applies to much more. This has hit the news in Marion County Florida, where a radio amateur in a senior’s community has shut down his radio station after a potential link emerged between it and another resident’s insulin pump. There is a legal challenge ongoing that relates to the complex’s rules over transmitting antennas.

It’s obviously a serious occurrence for an insulin pump to be affected by anything, and it sounds as though the radio amateur concerned has done the right thing. But it’s clear that something has gone badly wrong in this case whether it’s due to the amateur radio transmissions or not, because for a manufacturer to produce a medical device so easily affected by RF fields should be of concern to everyone. We’d hope that the FCC might take an interest in this story and get to the bottom of it in an impartial manner, because whether it’s the radio amateur at fault, the insulin pump, or something else entirely, it presents a risk to anyone dependent upon such a device.

Perhaps this might also be a case for the ARRL, as we’ve reported before they have some form when it comes to radio investigations.

[Main image source: MailariX, CC-BY-SA 4.0]

FM Radio, The Choice Of An Old Generation

Had the pandemic not upended many of this summer’s fun and games, many of my friends would have made a trip to the MCH hacker camp in the Netherlands earlier this month. I had an idea for a game for the event, a friend and I were going to secrete a set of those low-power FM transmitters as numbers stations around the camp for players to find and solve the numerical puzzles they would transmit. I even bought a few cheap FM transmitter modules from China for evaluation, and had some fun sending a chiptune Rick Astley across a housing estate in Northamptonshire.

To me as someone who grew up with FM radio and whose teen years played out to the sounds of BBC Radio 1 FM it made absolute sense to do a puzzle in this way, but it was my personal reminder of advancing years to find that some of my friends differed on the matter. Sure, they thought it was a great idea, but they gently reminded me that the kids don’t listen to any sort of conventional broadcast radio these days, instead they stream their music, so very few of them would have the means for listening to my numbers stations. Even for me it’s something I only use for BBC Radio 4 in the car, and to traverse the remainder of the FM dial is to hear a selection of easy listening, oldies, and classical music. It’s becoming an older person’s medium, and it’s inevitable that like AM before it, it will eventually wane.

There are two angles to this that might detain the casual hacker; first what it will mean from a broadcasting and radio spectrum perspective, and then how it is already influencing some of our projects.

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radio direction finding

Where’s That Radio? A Brief History Of Direction Finding

We think of radio navigation and direction finding as something fairly modern. However, it might surprise you that direction finding is nearly as old as radio itself. In 1888, Heinrich Hertz noted that signals were strongest when in one orientation of a loop antenna and weakest 90 degrees rotated. By 1900, experimenters noted dipoles exhibit similar behavior and it wasn’t long before antennas were made to rotate to either maximize signal or locate the transmitter.

British radio direction finding truck from 1927; public domain
British radio direction finding truck from 1927; public domain

Of course, there is one problem. You can’t actually tell which side of the antenna is pointing to the signal with a loop or a dipole. So if the antenna is pointing north, the signal might be to the north but it could also be to the south. Still, in some cases that’s enough information.

John Stone patented a system like this in 1901. Well-known radio experimenter Lee De Forest also had a novel system in 1904. These systems all suffered from a variety of issues. At shortwave frequencies, multipath propagation can confuse the receiver and while longwave signals need very large antennas. Most of the antennas moved, but some — like one by Marconi — used multiple elements and a switch.

However, there are special cases where these limitations are acceptable. For example, when Pan Am needed to navigate airplanes over the ocean in the 1930s, Hugo Leuteritz who had worked at RCA before Pan Am, used a loop antenna at the airport to locate a transmitter on the plane. Since you knew which side of the antenna the airplane must be on, the bidirectional detection wasn’t a problem.

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Surplus Syringes Make Satisfactory Tuner For Amateur Radio Experimentation

Amateur Radio as a hobby has a long history of encouraging experimentation using whatever one might have on hand. When [Tom Essenpreis] wanted to use his 14 MHz antenna outside of its designed frequency range, he knew he’d need an impedance matching circuit. The most common type is an L-Match circuit which uses a variable capacitor and a variable inductor to adjust the usable frequency range (resonance) of an antenna. While inefficient in some specific configurations, they excel at bridging the gap between the 50 ohm impedance of the radio and the unknown impedance of an antenna.

No doubt raiding his junk box for parts, [Tom] hacked together a variable capacitor and inductor using ferrite rods from AM radios, hot glue, magnet wire, copper tape, and some surplus 60ml syringes. You can see that he ground out the center of the plunger to make room for ferrite rods. Winding the outside of the syringe with magnet wire, the alignment of the ferrite can be adjusted via the plunger, changing the characteristics of the element to tune the circuit. [Tom] reports that he was able to make an on-air contact using his newly made tuner, and we’re sure he enjoyed putting his improvised equipment to use.

If Amateur Radio isn’t your thing, then maybe we can entice you with this syringe based rocket, syringe actuated 3D printed drill press, or vacuum syringe powered dragster. Have your own hack to share? By all means, submit it to the Tip Line!

Hackaday Podcast 131: Have A Heart, Transputer Pi, Just The Wing, And A Flipped Cable Fries Radio

Hackaday editors Mike Szczys and Elliot Williams recount the past week in hardware hacking. There’s a new Tamagochi hack that runs the original ROM on plain old microcontrollers like the STM32. Did you know you can blast the Bayer filter off a camera sensor using a powerful laser and the sensor will still work? We didn’t. There was a lot of debate this week about a commercial jet design alteration that would remove windows — but it’s for the good cause of making the plane more efficient. We marvel at what it takes to pump blood with an artificial heart, and go down the troubleshooting rabbit hole after the magic smoke was let out of a radio.

Take a look at the links below if you want to follow along, and as always, tell us what you think about this episode in the comments!

Direct download (60 MB or so.)

Places to follow Hackaday podcasts:

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