Radio Hacks

1359 Articles

Cloverleaf Satellite Antenna Mounted on a Pole

Tracking CubeSats For $25

June 1, 2018 by 11 Comments

CubeSats are tiny satellites which tag along as secondary payloads during launches. They have to weigh in at under 1.33 kg, and are often built at low cost. There’s even open source designs for these little spacecrafts. Over 800 CubeSats have been launched over the last few years, with many more launches scheduled in the near future.

[Thomas Cholakov] coupled a homemade cloverleaf antenna to a software-defined radio to track some of these satellites. The antenna is built out of copper-clad wire cut to the correct length to receive 437 MHz signals. Four loops are connected together and terminated to an RF connector.

This homebrew antenna is connected into a RTL-SDR dongle. The dongle picks up the beacon signals sent by the satellites and provides the data to a PC. Due to the motion of the satellites, their beacons can be easily identified by the Doppler shift of the frequency.

[Thomas] uses SDR Console to receive data from the satellites. While the demo only shows basic receiving, much more information on decoding these satellites can be found on the SDR Satellites website.

This looks like a fun weekend project, and probably the cheapest aerospace related project possible. After the break, watch the full video explaining how to build and set up the antenna and dongle.

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This Mostly 3D-Printed Discone Antenna Is Ready For Broadband Duty

May 29, 2018 by 16 Comments

For hams and other radio enthusiasts, the best part of the hobby is often designing antennas. Part black magic, part hard science, and part engineering, antenna design is an art. And while the expression of that art often ends up boiling down to pieces of wire cut to the correct length, some antennas have a little more going on in the aesthetics department.

Take the discone antenna, for example. Originally designed as a broadband antenna to sprout from aircraft fuselages, the discone has found a niche with public service radio listeners. But with a disk stuck to the top of a cone, the antennas have been a little hard to homebrew, at least until [ByTechLab] released this mostly 3D-printed discone. A quick look at the finished product, resembling a sweater drying rack more than a disc on top of a cone, reveals that the two shapes can be approximated by individual elements instead of solid surfaces. This is the way most practical discones are built, and [ByTechLab]’s Thingiverse page has the files needed to print the parts needed to properly orient the elements, which are just 6-mm aluminum rods. The printed hub pieces sandwich a copper plate to tie the elements together electrically while providing a feedpoint for the antenna as well as a sturdy place to mount it outdoors. This differs quite a bit from the last 3D-printed discone we featured, which used the solid geometry and was geared more for indoor use.

Interested in other antenna designs? Who can blame you? Check out the theory behind the Yagi-Uda beam antenna, or how to turn junk into a WiFi dish antenna.

[via RTL-SDR.com]

Ham Radio On $100 Or Less

May 28, 2018 by 63 Comments

There are a lot of reasons to get a ham radio license, and if you are one of those that think ham radio is dead you can probably skip this post. However, if you have been interested, but didn’t want to drop a lot of money on a station, [KE6MT] has got some great advice for you. He says you can have a rewarding time in ham radio for about $100 of spending.

The post is the advice he wished he had been given in 2015 when he got his license. It turns out you can get on the air very inexpensively these days, especially if you aren’t afraid to build gear from kits.

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Dual SDR Receives Two Bands At Once

May 21, 2018 by 15 Comments

There was a time when experimenting with software defined radio (SDR) was exotic. But thanks to cheap USB-based hardware, this technology is now accessible to anyone. While it is fun to play with the little $20 USB sticks, you’ll eventually want to move up to something better and there are a lot of great options. One of these is SDRPlay, and they recently released a new piece of hardware — RSPduo — that incorporates dual tuners.

We’ve talked about using the SDRPlay before as an upgrade from the cheap dongles. The new device can tune either a single 10 MHz band over the range of 1 kHz to 2 GHz, or you can select two 2 MHz bands. This opens up a lot of applications where you need to pick up signals in different areas of the spectrum (e.g., monitoring both sides of a cross-band repeater).

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Tiny Transmitter Brings Out The Spy Inside You

May 18, 2018 by 10 Comments

When it comes to surveillance, why let the government have all the fun? This tiny spy transmitter is just the thing you need to jumpstart your recreational espionage efforts.

We kid, of course — you’ll want to stay within the law of the land if you choose to build [TomTechTod]’s diminutive transmitter. Barely bigger than the 337 button cell that powers it, the scrap of PCB packs a fair number of surface mount components, most in 0201 packages. Even so, the transmitter is a simple design, with a two transistor audio stage amplifying the signal from the MEMS microphone and feeding an oscillator that uses a surface acoustic wave (SAW) resonator for stability. The bug is tuned for the 433-MHz low-power devices band, and from the video below, it appears to have decent range with the random wire antenna — maybe 50 meters. [TomTechTod] has all the build files posted, including Gerbers and a BOM with Digikey part numbers, so it should be easy to make one for your fieldcraft kit.

If you want to dive deeper into the world of electronic espionage, boy, have we got you covered. Here’s a primer on microphone bugs, a history of spy radios, or how backscatter was used to bug an embassy.

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Sign Of The Smith Chart Times

May 13, 2018 by 5 Comments

The Smith chart is a staple for analyzing complex impedance. [W2AEW] notes that a lot of inexpensive test gear like the MFJ-259B gives you complex readings, but fails to provide the sign of the imaginary part of the complex number. That makes it difficult to plot the results on a Smith chart or carry out other analysis. As you might expect, though, he has a solution for you that you can see in the video, below.

A common method is to increase the frequency slightly. In a simple case, you’d expect the imaginary part — the reactance — to go down for a capacitive impedance and up for an inductive one. Unfortunately, this doesn’t apply in many common cases, including when you are measuring through a transmission line which is probably what most people are doing with this type of test gear.

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HFT On HF, You Can’t Beat It For Latency

May 12, 2018 by 14 Comments

If you are a radio enthusiast of A Certain Age, you may well go misty-eyed from time to time with memories of shortwave listening in decades past. Countries across the world operated their own propaganda radio stations, and you could hear Radio Moscow’s take on world events, the BBC World Service responding, and Radio Tirana proudly announcing that every Albanian village now had a telephone. Many of those shortwave broadcast stations are now long gone, but if you imagine the HF spectrum is dead, think again. An unexpected find in an industrial park near Chicago led to an interesting look at the world of high-frequency trading, or HFT, and how they have moved to using shortwave links when everyone else has abandoned them, because of the unparalleled low latency they offer when communicating across the world.

Our intrepid tower-hunter is [KE9YQ], who was out cycling and noticed a particularly unusual structure adorned with a set of HF beams. These are the large directional antennas of the type you might otherwise expect to see on the roof of an embassy or in the backyard of a well-heeled radio amateur, and were particularly unusual in this otherwise unexciting part of America. There followed an interesting process of tracking down the site’s owners via the FCC permits for its operation, leading to the deduction of its purpose. With other antenna-hunters on the lookout for corresponding sites elsewhere in the world, it seems that this unusual global network hiding in plain sight could soon be revealed.

Unsurprisingly we’ve not covered many shortwave HFT stories. There are however other higher-latency ways to cross the world on HF.

Via SWLing Post, and thanks [W6MOQ] for the tip.