Pskov, Russia, is located about a dozen miles off the Estonian border and is home to about 200,000 people. It is also the home to a mysterious shortwave radio station which, inexplicably to most listeners, is constantly buzzing — and has been broadcasting since 1982.

UVB-76 is the station’s call letters but around radio listeners, it’s known as the Buzzer, after its hallmark sound and associated mystery. For twenty-four hours a day, the Buzzer makes about two dozen buzzing noises a minute. (You can listen to it here, but it’s loud — turn down your speakers first!) Over the course of its 30 year history, UVB-76 has switched from beeps to buzzes; from shorter tones to longer ones and back; and, on occasion, has a Russian speaker take to the airwaves, typically reading out numbers. Even the fall of the Soviet Union has not prevented UVB-76 from fulfilling its purpose.

That purpose, however, is entirely unknown to the general public. The Russian government not only refuses to disclose the reasons for UVB-76’s original and ongoing existence, but they also refuse to confirm its existence at all. So we don’t know what it’s broadcasting, why it’s broadcasting it, why it was moved hundreds of miles (originally, it was in forests just outside Moscow) in the fall of 2010, or why it stopped broadcasting on July 5, 2010, only to resume the next day.

What we do “know” is mostly conjecture. For example, at times, UVB-76 has broadcast snippets of muffled conversation, suggesting that there is an open microphone there. Sometimes (per this Wired article) the (intentionally broadcast) human voices on the broadcast read off strings of numbers, names, or otherwise unrelated words. This suggests that UVB-76 may be a “numbers station” — a hypothesized mechanism for communicating, via code, with spies out in the field — except that no government, to date, has confirmed that there is such thing as a numbers station at all.

Of course, if UVB-76 is a tool for espionage, that makes its longevity even more puzzling — given that the station was set up by the now-defunct Soviet Union, yet is currently maintained by its political successor.

Bonus fact : Numbers stations (if they exist) aren’t used solely by (former) Soviets. There’s something, believed to be near Albuquerque, New Mexico, broadcasting a series of messages lasting a total of two minutes, always starting seven seconds after the hour. The station is nicknamed Yosemite Sam, after the Looney Tunes character of the same name. Why? Because a clip of Yosemite Sam ends each broadcast — he says “Varmint, I’m a-gonna b-b-b-bloooow yah t’smithereens!” per the radio station’s Wikipedia entry. Much like UVB-76, the public is entirely unaware as to why the station exists and similarly, why it plays a classic cartoon clip two dozen times a day.

From the Archives: Sounds from the Deep: More unknown sounds.

Related: A book of one million random numbers, in case you want to start your own numbers station and are afraid of accidentally, and subconsciously, developing a pattern. A bargain at just under $90.00.