Radio Hacks

1434 Articles

1950’s AM Transmitter Is Fun But Dangerous

July 29, 2018 by 39 Comments

[Mr. Carlson] bought a Globe Scout Model 40A ham radio transmitter at a hamfest. The 40A was a grand old transmitter full of tubes, high voltage, and a giant transformer. It is really interesting to see how much things have changed over the years. The transmitter is huge but has comparatively few parts. You needed a crystal for the frequency you wanted to talk. There were two little modules that were precursors to hybrid circuits (which were precursors to ICs) that were often called PECs or couplates (not couplets) but other than those, it is all tubes and discrete components beautifully wired point-to-point.

The really surprising part, though, is the back panel. There’s a screw terminal to drive the coil of an external coaxial relay that has line voltage on it. There’s also a plug on the back with exposed terminals that has plate voltage on it which is considerable. In the 1950s, you assumed people operating equipment like this would be careful not to touch exposed high voltage.

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Why Have Only One Radio, When You Can Have Two?

July 28, 2018 by 4 Comments

There are a multitude of radio shields for the Arduino and similar platforms, but they so often only support one protocol, manufacturer, or frequency band. [Jan Gromeš] was vexed by this in a project he saw, so decided to create a shield capable of supporting multiple different types. And because more is so often better, he also gave it space for not one, but two different radio modules. He calls the resulting Swiss Army Knife of Arduino radio shields the Kite, and he’s shared everything needed for one on a hackaday.io page and a GitHub repository.

Supported so far are ESP8266 modules, HC-05 Bluetooth modules, RFM69 FSK/OOK modules, SX127x series LoRa modules including SX1272, SX1276 and SX1278, XBee modules (S2B), and he claims that more are in development. Since some of those operate in very similar frequency bands it would be interesting to note whether any adverse effects come from their use in close proximity. We suspect there won’t be because the protocols involved are designed to be resilient, but there is nothing like a real-world example to prove it.

This project is unique, so we’re struggling to find previous Hackaday features of analogous ones. We have however looked at an overview of choosing the right wireless tech.

Building An SDR Lab With Wheels

July 27, 2018 by 11 Comments

With the incredibly low cost of software defined radio (SDR) hardware, and the often zero cost of related software, there’s never been a better time to get into the world of radio. If you’ve got $30 burning a hole in your pocket, you’re good to go. But as with any engrossing hobby that’s cheap to get into, you run the risk of going overboard eventually.

For example, if the radio gear inside your car approaches parity with the Kelly Blue Book value of said vehicle, you may have been bitten by the radio bug. In the video after the break, [Corrosive] gives us a tour of his antenna festooned Hyundai Accent, that features everything he needs to receive and analyze a multitude of analog and digital radio signals on the go.

He starts with the roof of the car, which is home to five whip antennas (not counting the one from the factory installed AM/FM radio) and two GPS receivers. The ones on the rear of the car feed down into the trunk, where a bank of Nooelec NESDR RTL-SDR receivers will live in a USB hub. He’s only got one installed for test purposes, but he’ll need more for everything he’s got planned. Also riding in the back is a BCD780XLT scanner, which he got cheap on eBay thanks to the fact it had a dead display.

Luckily, where [Corrosive] is going, he won’t need displays. The SDR receivers and the scanner are all controlled from the driver’s seat by way of a Windows 10 tablet. This runs the ProScan software that provides a virtual interface to the BCD780XLT, as well as various SDR interfaces. He’s also got Gpredict for tracking satellites and ADS-B programs like Virtual Radar.

The car’s head unit has been replaced by a rooted Android entertainment system which supports USB host mode. [Corrosive] says it isn’t hooked up yet, but in the future the head unit is going to get its own SDR receiver so he can run programs like RF Analyzer right in the dashboard. We’re willing to bet that this will be the only car in the world that has both a waterfall display and the “Check Engine” light on at the same time.

Even if you aren’t ready to install it in your car, you might like to read up on using multiple SDR receivers for trunked radio or setting up your own ADS-B receiver to get a better idea of what [Corrosive] has in mind once everything is up and running.

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HOPE XII: Time Travel With Software Defined Radio

July 23, 2018 by 51 Comments

It’s easy to dismiss radio as little more than background noise while we drive.  At worst you might even think it’s just another method for advertisers to peddle their wares. But in reality it’s a snapshot of the culture of a particular time and place; a record of what was in the news, what music was popular, what the weather was like, basically what life was like. If it was important enough to be worth the expense and complexity of broadcasting it on the radio, it’s probably worth keeping for future reference.

But radio is fleeting, a 24/7 stream of content that’s never exactly the same twice. Yet while we obsessively document music and video, nobody’s bothering to record radio. You can easily hop online and watch a TV show that originally aired 50 years ago, but good luck finding a recording of what your local radio station was broadcasting last week. All that information, that rich tapestry of life, is gone and there’s nothing we can do about it.

Or can we? At HOPE XII, Thomas Witherspoon gave a talk called “Creating a Radio Time Machine: Software-Defined Radios and Time-Shifted Recordings”, an overview of the work he’s been doing recording and cataloging the broadcast radio spectrum. He demonstrated how anyone can use low cost SDR hardware to record, and later play back, whole chunks of the AM and shortwave bands. Rather than an audio file containing a single radio station, the method he describes allows you to interactively tune in to different stations and explore the airwaves as if it were live.

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Digital Attenuator Goes From Manual To Arduino Control

July 21, 2018 by 6 Comments

[Kerry Wong] comes across the coolest hardware, and always manages to do something interesting with it. His widget du jour is an old demo board for a digital RF attenuator chip, which can pad a signal in discrete steps according to the settings of some DIP switches. [Kerry]’s goal: forget the finger switch-flipping and bring the attenuator under Arduino control.

As usual with his videos, [Kerry] gives us a great rundown on the theory behind the hardware he’s working with. The chip in question is an interesting beast, an HMC624LP4E from Hittite, a company that was rolled into Analog Devices in 2014. The now-obsolete device is a monolithic microwave integrated circuit (MMIC) built on a gallium arsenide substrate rather than silicon, and attenuates DC to 6-GHz signals in 64 steps down to -31.5 dBm. After a functional check of the board using the DIP switches, he whipped up a quick Arduino project to control the chip with its built-in serial interface. It’s just a prototype for now, but spinning the encoder is a lot handier than flipping switches, and once this is boxed up it’ll make a great addition to [Kerry]’s RF bench.

If this video puts you in an RF state of mind, check out some of [Kerry]’s other videos, like this one about temperature-compensated crystal oscillators, or the mysteries of microwave electronics.

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Harley-Hardened Wire Helps High-Gain Antenna Hack

July 18, 2018 by 46 Comments

What does a Harley-Davidson motorcycle have to do with building antennas? Absolutely nothing, unless you happen to have one and need to work-harden copper wire to build a collinear antenna for LoRa.

We’ll explain. Never being one to settle, [Andreas Spiess] needed a better antenna for his LoRa experiments. Looking for high gain and an omnidirectional pattern, he bought a commercial colinear antenna, which is a wire with precisely spaced loops that acts like a stack of dipoles. Sadly, in a head-to-head test [Andreas] found that the commercial antenna was no better than lower gain antennas in terms of range, and so he decided to roll his own.

Copper wire is a great material for antennas since it can be easily formed without special tools and it solders like a champ. But the stuff you get at the home center is nowhere near stiff enough for a free-standing vertical whip. This is where the Harley came in: [Andreas] used his Hog to stretch out the 1.75-mm diameter (a little bigger than #14 AWG) copper wire. Not only did the work-hardening stiffen the wire, it reduced its diameter to the 1.4 mm needed for the antenna design. His vector network analyzer told him that ground-plane elements and a little fiddling with the loop diameter were needed to get the antenna to resonate at 868 MHz, but in the end it looks like the antenna is on track to deliver 5-dBi of gain.

Of course there are plenty of other ways to stretch out a wire — you could just stretch it out with hanging weights, or even with a go-kart motor-powered winch if you’re ambitious. But if you’ve got a bike like that, why not flaunt it?

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The Biggest Corner Antenna We’ve Ever Seen

July 17, 2018 by 23 Comments

Radio waves are received on antennas, for which when the signal in question comes over a long distance a big reflector is needed. When the reception distance is literally astronomical, the reflector has to be pretty darn big. [The Thought Emporium] wants to pick up signals from distant satellites, the moon, and hopefully a pulsar. On the scale of home-built amateur radio, this will be a monstrous antenna. The video also follows the break.

In hacker fashion, the project is built on a budget, so all the parts are direct from a hardware store, and the tools are already in your toolbox or hackerspace. Electrical conduit, chicken wire, PVC pipes, wood blocks, and screws make up most of the structure so put away your crazy links to Chinese distributors unless you need an SDR. The form of the antenna is the crucial thing, and the shape is three perpendicular panels as seen in the image and video. The construction in the video is just a suggestion, but it doesn’t involve welding, so that opens it to even more amateurs.

Even if you are not trying to receive a pulsar’s signature, we have hacks galore for radios and antennas.

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