The RFI Hunter: Looking For Noise In All The Wrong Places

January 15, 2020 by Dan Maloney 22 Comments

Next time you get a new device and excitedly unwrap its little poly-wrapped power supply, remember this: for every switch-mode power supply you plug in, an amateur radio operator sheds a tear. A noisy, broadband, harmonic-laden tear.

The degree to which this fact disturbs you very much depends upon which side of the mic you’re on, but radio-frequency interference, or RFI, is something we should all at least be aware of. [Josh (KI6NAZ)] is keenly aware of RFI in his ham shack, but rather than curse the ever-rising noise floor he’s come up with some helpful tips for hunting down and eliminating it – or at least reducing its impact.

Attacking the problem begins with locating the sources of RFI, for which [Josh] used the classic “one-circuit-at-a-time” approach – kill every breaker in the panel and monitor the noise floor while flipping each breaker back on. This should at least give you a rough idea of where the offending devices are in your house. From there, [Josh] used a small shortwave receiver to locate problem areas, like the refrigerator, the clothes dryer, and his shack PC. The family flat-screen TV proved to be quite noisy too. Remediation techniques include wrapping every power cord and cable around toroids or clamping ferrite cores around them, both on the offending devices and in the shack. He even went so far as to add a line filter to the dryer to clamp down on its unwanted interference.

Judging by his waterfall displays, [Josh]’s efforts paid off, bringing his noise floor down from S5 to S1 or so. It’s too bad he had to take matters into his own hands – it’s not like the FCC and other spectrum watchdogs don’t know there’s a problem, after all.

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Radio Piracy On The High Seas: Commercial Demand For Taboo Music

April 24, 2019 by Al Williams 32 Comments

The true story of pirate radio is a complicated fight over the airwaves. Maybe you have a picture in your mind of some kid in his mom’s basement playing records, but the pirate stations we are thinking about — Radio Caroline and Radio Northsea International — were major business operations. They were perfectly ordinary radio stations except they operated from ships at sea to avoid falling under the jurisdiction of a particular government.

Back then many governments were not particularly fond of rock music. People wanted it though, and because people did, advertisers wanted to capitalize on it. When people want to spend money but can’t, entrepreneurs will find a way to deliver what is desired. That’s exactly what happened.

Of course, if that’s all there was to it, this wouldn’t be interesting. But the story is one of intrigue with armed boardings, distress calls interrupting music programs, and fire bombings. Most radio stations don’t have to deal with those events. Surprisingly, at least one of these iconic stations is still around — in a manner of speaking, anyway.

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This SDR Uses A Tube

March 7, 2019 by Al Williams 17 Comments

When you think of a software defined radio (SDR) setup, maybe you imagine an IC or two, maybe feeding a computer. You probably don’t think of a vacuum tube. [Mirko Pavleski] built a one-tube shortwave SDR using some instructions from [Burkhard Kainka] which are in German, but Google Translate is good enough if you want to duplicate his feat. You can see a video of [Mirko’s] creation, below.

The build was an experiment to see if a tube receiver could be stable enough to receive digital shortwave radio broadcasts. To avoid AC line hum, the radio is battery operated and while the original uses an EL95 tube, [Mirko] used an EF80.

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

May 12, 2018 by Jenny List 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.

Listen To The Globe

January 2, 2017 by Al Williams 19 Comments

There was a time when electronic hackers (or hobbyist, enthusiasts, geeks, or whatever you want to be called) were better than average at geography. Probably because most of us listened to shortwave radio or even transmitted with ham radio gear. These days, if you try listening to shortwave, you have to be pretty patient. Unless you want to hear religious broadcasters or programming aimed at the third world, there’s not much broadcast traffic to listen to anymore

The reason, of course, is the Internet. But we’ve often thought that it isn’t quite the same. When you tuned in London on your homebrew regenerative receiver, you wanted to know where that voice was coming from, and you couldn’t help but learn more about the area and the people who live there. Tune into a BBC live stream on the Internet, and it might as well be any other stream or podcast from anywhere in the world.

The New Shortwave

Maybe we need to turn kids on to Radio Garden. Superficially, it isn’t a big deal. Another catalog of streaming radio stations. You can find plenty of those around. But Radio Garden has an amazing interface (and a few other unique features). That interface is a globe. You can see dots everywhere there’s a broadcast station and with a click, you are listening to that station. The static and tuning noises are a nice touch.

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Five-Watt SDR Transceiver For Hams

November 20, 2016 by Elliot Williams 50 Comments

The availability of cheap SDR hardware created a flourishing ecosystem for SDR software, but a lot of the hardware driving the revolution was still “cheap”. In the last few years, we’ve seen quality gear replacing the TV dongles in many setups, and down-converters designed for them to allow them to work on the ham bands.

But something that’s purpose-built might be a better option if ham radio, particularly the shortwave portion thereof, is your goal. First off, you might want to transmit, which none of the TV dongles allow. Then, you might want a bit of power. Finally, if you’re serious about short-wave, you care more about the audio quality than you do immense bandwidth, so you’re going to want some good filters on the receiving end to help you pull the signal out of all the noise.

The RS-HFIQ 5 W SDR transceiver might be for you. It’s up on Kickstarter right now, and it’s worth looking at if you want a fully open source (schematics, firmware, and software) shortwave SDR rig. It’s also compatible with various open frontends.

The single-board radio isn’t really a full SDR in our mind — it demodulates the radio signal and sends a 96 kHz IQ signal across to your computer’s soundcard where it gets sampled and fully decoded. The advantage of this is that purpose-built audio rate DACs have comparatively high resolution for the money, but the disadvantage is that you’re limited to 96 kHz of spectrum into the computer. That’s great for voice and code transmissions, but won’t cut it for high-bandwidth data or frequency hopping applications. But that’s a reasonable design tradeoff for a shortwave.

Still, an SDR like this is a far cry from how simple a shortwave radio can be. But if you’re looking to build up your own SDR-based shortwave setup, and you’d like to hack on the controls more than on the radio itself, this looks like a good start.

Cache Shortwave Signals For Later With This SDR Spectrum Grabber

November 18, 2016 by Dan Maloney 6 Comments

Shortwave listening has always been a mainly nocturnal hobby. To get the real DX, one had to wait for favorable ionospheric conditions after sunset and spend hours twisting knobs while straining to pick voices from half a planet away out of the noise. But who has time for that in today’s world? And what of the poor city-dwelling SWL, with antenna limitations and often elevated noise floor in the urban jungle?
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