Radio Hacks

1461 Articles

Visually Tune Your HF Antenna Using An Oscilloscope And Signal Generator

September 20, 2013 by 15 Comments

Lots of readers are into toying around with RF and ham radios. One thing that is always of concern is tuning the antenna. New equipment is never cheap, so whenever another option comes along that uses existing test gear it gets our attention. [Alan Wolke] aka [w2aew] covers a process he uses to tune his HF antenna using a signal generator and oscilloscope.

The process is more of a teaching aid than a practical replacement for commercial equipment mostly because proper signal generators and oscilloscopes are large items and sometimes not available or affordable. That said, if you do have such test gear you only need build a simple breakout board containing a form of wheatstone bridge where the unknown Rx is the antenna. Two oscilloscope probes are connected across the bridge balance nodes. Some special care needs to be taken matching probe cable length and 50 ohm input impedance to the oscilloscope. A couple of 1K probe coupling resistors are also needed to prevent affecting the impendence at the hookup points. Once the selected signal is injected you can adjust an antenna tuner until the two voltage waveforms match on the oscilloscope indicating your antenna network is tuned to 50 ohm impedance with no reactance.

Being able to tune your antenna visually can really help you understand what is going on in the turning process; matching not only input impedance but also phase shift indicating inductive or capacitive reactance. Join us after the break to see the video and for information on what’s presented in the second part of [Alan’s] presentation.

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Aux-in On A 30 Year Old Boombox

September 17, 2013 by 26 Comments

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[Michael] just sent us this nice example of some good ol’ fashioned radio hacking.

He originally received the radio from his grandmother, and while he doesn’t listen to the radio much, he felt he couldn’t just let it go to waste. So like any good hacker he cracked open the case and took a look inside.

The beauty with radios from the 80’s is the simplicity of it all. They typically have single layer PCBs and nice big components which makes it so much easier to tinker with.

He used a bench power supply to bypass the main transformer for safety’s sake, and began probing the various points. The cassettes audio output was the easiest to find, but unfortunately it required the play button to be activated. Not wanting to lose functionality (or have an annoying rattling cassette mechanism), he continued probing and eventually found similar wires coming from the radio part of the PCB. Upon further probing he discovered he could trick the radio band button so that the radio would be off, but the output could still be used. After that it was just a matter of wiring, soldering, and adding an auxiliary plug to the case.

We’ve covered lots of auxiliary port hacks in the past, but this one is a great example of saving old technology from the dump.

[Thanks Michael!]

Digital Camera Becomes Video Transmitter

September 12, 2013 by 21 Comments

canon

In the arena of high altitude balloons, Canon’s PowerShot series of digicams are the camera du jour for sending high into the stratosphere. There’s a particular reason for this: these cameras can run the very capable CHDK firmware that turns a $100 digicam into a camera with a built-in intervalometer along with a whole bunch of really cool features. It appears this CHDK firmware is much more powerful than we imagined, because [Chris] is now transmitting pictures taken from a Canon a530 to the ground, using only the CHDK firmware and a cheap radio module.

These PowerShot cameras have an ARM processor inside that runs VxWorks, a minimal but very capable OS for embedded devices and Mars rovers. By tying in to the Tx and Rx lines of the camera, [Chris] can issue commands to the OS, change settings, and even install his own code.

With the help of [Phil Heron]’s SSDV encoder written in C, [Chris] was able to get the camera to transmit images  with a small radio transmitter that fits in the battery compartment. Right now, [Chris] has only built the CHDK + SSDV for the Canon a530, but with how useful this build is, we expect to see an improved version very shortly.

An RTL-SDR Spectrum Analyzer

September 9, 2013 by 15 Comments

With the combination of small, powerful, and pocketable computers and cheap, off-the-shelf software defined radio receivers, it was only a matter of time before someone built a homebrew spectrum analyzer with these ingredients. This great build is the project of [Stephen Ong] and he’s even released all the softwares for you to build this on your own.

The two main components of this build are a BeagleBone Black and its 7″ Touchscreen cape. The BeagleBone is running Angstrom Linux, a blazingly fast Linux distro for small embedded devices. The radio hardware consists of only a USB TV tuner supported by RTL-SDR. In his demo video, [Stephen] shows off his project and by all accounts it is remarkable, with a UI better than most desktop-oriented SDR software suites.

You can grab the BeagleBone image [Stephen] is using over on his blog, but for more enterprising reader, he’s also put up the source of his ViewRF software up on GitHub.

A Comparison Of Hacker Friendly SDRs

August 23, 2013 by 61 Comments

In the market for a software defined radio? [Taylor Killian] wrote a comprehensive comparison of several models that are within the price range of amateurs and hobbyists.

You can get started with SDR using a $20 TV tuner card, but there’s a lot of limitations. These cards only work as receivers, are limited to a small chunk of the radio spectrum, and have limited bandwidth and sample rates. The new SDRs on the market, including the bladeRF, HackRF, and USRP offerings are purpose built for SDR experimentation. You might want an SDR to set up a cellular base station at Burning Man, scan Police and Fire radio channels, or to track ships.

[Taylor] breaks down the various specifications of each radio, and discusses the components used in each SDR in depth. In the end, the choice depends on what you want to do and how much you’re willing to spend. This breakdown should help you choose a hacker friendly SDR.

HackRF, Or Playing From 30 MHz To 6 GHz

August 1, 2013 by 49 Comments

Up on Kickstarter, [Michael Ossmann] is launching the HackRF, an inordinately cheap, exceedingly capable software defined radio tool that’s small enough to lose in your laptop bag.

The HackRF was the subject of a lot of interest last time it was on Hackaday – the ability to receive up to 6GHz allows the HackRF to do a lot of very interesting things, including listening in on Bluetooth, WiFi, and 4G networks. Also, the ability to transmit on these frequencies means a lot of very interesting, and quite possibly slightly evil applications are open to anyone with a HackRF. Like the RTL-SDR dongles, the HackRF works with GNU Radio out of the box, meaning all those cool SDR hacks we’ve seen so far will work with this new, more powerful board.

Compared to the USB TV tuner cards that were so popular a year ago, the HackRF has 10 times the bandwidth, is able to receive up to 6GHz, and is also able to transmit. It’s only half-duplex, so to receive and transmit simultaneously you’ll need two HackRFs, or maybe wait for a hardware revision that will hopefully come sooner rather than later.

Below you can check out [Michael]’s presentation at Toorcon where the HackRF was unleashed to the world.

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Retrotechtacular: A Tour Of WLW, A 500,000 Watt Radio Transmitter

July 26, 2013 by 61 Comments

retrotechtacular-wlw-transmitter-tour

This is an overview of a 500,000 Watt radio transmitter site. It’s one of the slides shared in a guided video tour of the transmitter’s hardware. The radio station — whose call sign was WLW — called itself the Nation’s Station because of its ability to reach so much of the country.

It operated at the 500 kW level starting back in the 1930’s. The technology at the time meant that there were a lot of challenges involved with transmitting at this level of power. It took 750 kW input to achieve the 500 kW output. To reach that the station had a set of AC motors in the basement generating the 4500 Amps at 33 Volts DC needed to power the transmitter to heat each filament. Obviously there was a lot of heat generated at the same time. The system was water-cooled. An elaborate network of Pyrex pipes carried distilled water to and from the tubes to handle the heat dissipation.

The video tour lasts about thirty minutes. It’s just packed with interesting tidbits from the experts leading the tour so add it to your watch list for some geeky entertainment over the weekend.

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