Want to listen to spy broadcasts? Here's how.

Hidden among the squelch and whine of the little used shortwave radio band, mysterious stations broadcast unbreakable code.

Yosemite Sam threatens to blow the listener to smithereens before switching to a different frequency. An upbeat woman delivers nonsensical strings of numbers in Mandarin. A repeating broadcast of a nursery rhyme breaks only for a child to read numbers in German.

These are the numbers stations — a radio station on shortwave that broadcasts some sort of repetitive noise followed by strings of numbers. Amateur tech geeks first identified the stations after World War II. No one is sure what their purpose is.

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That hasn't stopped anyone from speculating. The most popular theory is that the broadcasts are used to transmit coded messages to spies and the military. Shortwave is easy to broadcast globally, hard to trace and free of commercial traffic.

Spies or military personnel tune into the frequency at an appointed time and use a one-time pad to decrypt the message. The spy then destroys the pad and goes about their mission. Anyone else listening hears a random string of numbers with no context.

Listening to numbers stations was once the hobby of a small margin of the population. Only those with shortwave radios and patience to tune them reaped the benefits of the strange broadcasts.

Now — thanks to the internet — anyone can listen.

The University of Twente in the Netherlands maintains web-based shortwave radio anyone can access here. The interface is simple. Just input the frequency you want in the box below the graphic.

To get an idea of what frequencies to check out, head over to Priyom.org — an international group researching intelligence and military communications via shortwave radio. The site maintains a schedule of active shortwave stations and catalogs interesting activity.

If you find an interesting broadcast, post it to our Facebook page. To get you started, here are two of War is Boring's favorite numbers stations.

The buzzer

Tune the dial to 4625 kHz and you'll hear a repetitive buzzing noise. This obnoxious station goes by the call sign UVB-76, but shortwave aficionados call it The Buzzer. The Buzzer has been blaring that tone since the early 1980s.

On occasion, the buzzing stops. A voice comes on and reads numbers and letters in Russian. The speculation is that the The Buzzer has something to do with Russian military operations or intelligence, but that's never been confirmed.

Yosemite Sam

The cranky gunslinger from old Bugs Bunny cartoons began screaming across the shortwave band around 2004. He's hard to pinpoint because he moves. But you can typically find him at 3700 kHz or 6500 kHz.

Every broadcast begins with a millisecond-long compressed data burst followed by a sound clip of Yosemite Sam. The data burst and sound clip then moves to a higher frequency. This broadcast is repeated over a two minute period before receding back into the darkness.

To date, no one has decoded the data burst. Estimates trace the signal's origin to somewhere in the deserts of New Mexico. Here's a clip of the oddity.

Cold War legacy

It's tempting to think of the numbers stations as a relic of the past. The image of a forgotten radio transmitter blaring out strange messages for no one is a romantic one.

But that's false. Yosemite Sam didn't get started until 2004. The Buzzer had a coded broadcast on July 10, 2014.

These numbers stations are still very much in use. Just ask Cuba.

In the late 1990s, the FBI busted a group of Cuban spies known as the Wasp's Network. The five Cuban intelligence officers received messages from back home via a shortwave radio station transmitting numbers. The coded messages were a large part of the FBI's court case.

It was the only time a government publicly acknowledged the existence and purpose of the numbers stations.

So remember as you're listening to the repetitive buzz out of Russia or a woman reading numbers in a foreign language … these messages are meant for someone. You aren't the only one listening.

From drones to AKs, high technology to low politics, War is Boring explores how and why we fight above, on, and below an angry world. Sign up for its daily email update here or subscribe to its RSS Feed here.

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