Owning A ShortWave Radio Is Once Again A Subversive Activity

March 17, 2022 by 149 Comments

An abiding memory for a teen fascinated by electronics and radio in the 1970s and 1980s is the proliferation of propaganda stations that covered the shortwave spectrum. Some of them were slightly surreal such as Albania’s Radio Tirana which would proudly inform 1980s Western Europe that every village in the country now possessed a telephone, but most stations were the more mainstream ideological gladiating of Voice of America and Radio Moscow.

It’s a long-gone era as the Cold War is a distant memory and citizens East and West get their info from the Internet, but perhaps there’s an echo of those times following the invasion of the Ukraine. With most external news agencies thrown out of Russia and their websites blocked, international broadcasters are launching new shortwave services to get the news through. Owning a shortwave radio in Russia may once again be a subversive activity. Let’s build one!

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Shortwave Radio Picks Up Sideband

September 29, 2021 by 14 Comments

With the push to having most of a radio receiver as part of a PC, it might seem odd to have a standalone communication receiver, but [OM0ET] reviews the latest one he picked up, an ATS25. Inside isn’t much: a battery, a speaker, an encoder, and a Si4732 that provides the RF muscle.

It appears the receiver is pretty broadband which could be a problem. [OM0ET] suggests adding selectivity in the antenna or adding an extra board to use as a bandpass filter.

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Web Pages (and More) Via Shortwave

March 13, 2021 by 30 Comments

If you are a ham radio operator, the idea of sending pictures and data over voice channels is nothing new. Hams have lots of techniques for doing that and — not so long ago — even most data transmissions were over phone lines. However, now everyone can get in on the game thanks to the cheap availability of software-defined radio. Several commercial shortwave broadcasters are sending encoded data including images and even entire web pages. You can find out more at the Swradiogram website. You can also find step-by-step instructions.

WINB in Pennsylvania and WRMI Florida both have shows that include interspersed data. To play along, you’ll need a decoder like Fldigi or TIVAR. If you don’t have sufficient radio gear, you can probably borrow some from the Internet.

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Comparing Shortwave Antennas With RTL-SDR And Python

September 5, 2020 by 7 Comments

Measuring the performance of antennas in absolute terms that can involve a lot of expensive equipment and specialized facilities. For practical applications, especially when building antennas, comparing performance in relative terms is more practical. Using cheap RTL-SDR dongles and Python, [Eric Urban] was able to compare the performance of two shortwave/HF antennas, and documented the entire process.

The two antennas in question was a single band inverted-L and smaller broadband T3FD antenna. [Eric] first gathered performance data for each over few days, connected to separate PCs with RTL-SDRs via low-pass filters. These were set up to receive FT8 transmissions, a popular digital ham radio mode, which allowed [Eric] to automate data collection completely. GQRX, a software receiver, converted the signals to audio, which was then piped into WSJT-X for demodulation.

Data for each received FT8 transmission was recorded to a log file. [Eric] also modified GQRX and WSJT-X to give him all the remote control features he needed to automatically change frequencies. Between the two antenna setups, more than 100,000 FT8 transmissions were logged. Using the recorded data and Python he compared the number of received transmissions, the distance, and the heading to the transmitters, using the location information included in many FT8 transmissions. Where the same transmission was received by both antennas, the signal-to-noise ratios was compared.

From all this data, [Eric] was able to learn that the inverted-L antenna performed better than the T3FD antenna on three of the four frequency bands that were tested. He also discovered that the inverted-L appeared to be “deaf” in one particular direction. Although the tests weren’t perfect, it is impressive how much practical data [Eric] was able to gather with low-cost hardware. Continue reading “Comparing Shortwave Antennas With RTL-SDR And Python” →

Radio Shack Shortwave Goes Digital

May 20, 2020 by 26 Comments

If you spent the 1970s obsessively browsing through the Radio Shack catalog, you probably remember the DX-160 shortwave receiver. You might have even had one. The radio looked suspiciously like the less expensive Eico of the same era, but it had that amazing-looking bandspread dial, instead of the Eico’s uncalibrated single turn knob number 1 to 10. Finding an exact frequency was an artful process of using both knobs, but [Frank] decided to refit his with a digital frequency display.

Even if you don’t have a DX-160, the techniques [Frank]  uses are pretty applicable to old receivers like this. In this case, the radio is a single conversion superhet with a variable frequency oscillator (VFO), so you need only read that frequency and then add or subtract the IF before display. If you can find a place to tap the VFO without perturbing it too much, you should be able to pull the same stunt.

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Homebrew Loop Antenna Brings The Shortwave World To You

April 12, 2020 by 36 Comments

Radio may be dead in terms of delivering entertainment, but it’s times like these when the original social network comes into its own. Being able to tune in stations from across the planet to get fresh perspectives on a global event can even be a life saver. You’ll need a good antenna to do that, which is where this homebrew loop antenna for the shortwave radio bands shines.

To be honest, pretty much any chunk of wire will do as an antenna for most shortwave receivers. But not everyone lives somewhere where it’s possible to string up a hundred meters of wire and get a good ground connection, which could make a passive loop antenna like this a good choice. Plus, loops tend to cancel the electrical noise that’s so part of life today, which can make it easier to pull in weak, distant stations.

[Thomas]’s design is based on a length of coaxial cable, which should be stiff enough to give the loop some stability, like a low-loss RG-8 or RG-213. The coax braid and dielectric are exposed at the midpoint of the cable to create a feed point, while the shield and center conductor at the other ends are cross-connected. A 1:1 transformer is wound on a toroid core to connect to the feedpoint; [Thomas] calls it a balun but we tend to think it’s more of an unun, since both the antenna and feedline are unbalanced. He reports good results from the loop across the shortwave band.

The shortwave and ham bands are a treasure trove of information and entertainment just waiting to be explored. Check them out — you might learn something, and you might even stumble across spies doing their thing.

[via RTL-SDR.com]

RF Shield Turns Arduino (And PC) Into Shortwave Radio

February 14, 2020 by 10 Comments

Microcontrollers tend to consume other kinds of electronics. A project you might once have done with a 555 now probably has a cheap microcontroller in it. Music synthesizers? RC controllers? Most likely, all microcontroller-based now. We always thought RF electronics would be immune to that, but the last decade or two has proven us wrong. Software-defined radio or SDR means you get the RF signal to digital as soon as possible and do everything else in software. If you want an introduction to SDR, Elektor now has an inexpensive RF shield for the Arduino. The Si5351-based board uses that oscillator IC to shift RF signals down to audio frequencies and then makes it available to the PC to do more processing.

The board is available alone or as part of a kit that includes a book. There’s also a series of Elektor articles about it. There’s also a review video from Elektor about the board in the video, below.

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