http://www.wired.co.uk/article/russian-numbers-station-broadcast-changes

2010 story:

The output of a mysterious radio station in Russia, which has been broadcasting the same monotonous signal almost continuously for 20 years, has suddenly changed.

Numbers stations are shortwave radio stations that broadcast computer-generated voices reading numbers, words, letters or Morse code. Their purpose has never been uncovered, but evidence from spy cases suggests that they're used to broadcast coded information to secret agents.

Over the past week or so, the output of one particular station that broadcasts from near Povarovo, Russia, increased dramatically. The station has a callsign of UVB-76, but is known as "The Buzzer" by its listeners because of the short, monotonous buzz tone that it normally plays 21 to 34 times per minute. It's only deviated from that signal three times previously -- briefly in 1997, 2002 and 2006.

In early August, a garbled recording of a voice speaking Russian was heard by listeners. A few days later, on 23 August at 13:35UTC, a clearer voice read out the following message twice: "UVB-76, UVB-76 — 93 882 naimina 74 14 35 74 — 9 3 8 8 2 nikolai, anna, ivan, michail, ivan, nikolai, anna, 7, 4, 1, 4, 3, 5, 7, 4", before returning to its normal broadcasting.

Since then, a number of other distorted voices have appeared over the normal buzzing transmission, as well as knocks and shuffles, as if someone were moving things around inside the broadcasting room. It's believed that the transmission site has an open microphone, which occasionally picks up sounds from technicians working within the broadcast site.

Various fans of the station have begun the process of trying to decode the signal. Interpreting the numbers as co-ordinates gives a location in the middle of the Barents Sea, between Norway and Russia, where there's large scale oil and gas production, and where the Russian army plans to test anti-aircraft missiles in the near future.

Others suspect that it might be a transmission that signals the availability of another system -- like a dead man's switch, possibly even for Russia's Cold War-era Dead Hand fail-deadly system, which was to trigger ICBM launches if a nuclear strike from the United States was detected. Since the fall of the Soviet Union, it may have been repurposed.

The transmissions continue, and are being documented on the Wikipedia page for the station. If you'd like to help, it's possible to listen in yourself, as one fan has rigged up a web stream of the signal. It's currently very busy, however, so if you have difficulty tuning in, then try again later.

Volume dials were turned up, computers began recording, forum posts were hastily typed. Something big was happening.

OBYaVLENIYA KOMANDA 135
For the first time in a history that stretches back nearly 40 years, the mysterious Russian radio signal popularly known as UVB-76 had issued an order. On Jan. 24, 2013, it was heard clearly by its legion of fans:

Command 135 initiated
The radio signal that occupies 4625 kHz has reportedly been broadcasting since the late 1970s. The earliest known recording of it is dated 1982. Ever since curious owners of shortwave radios first discovered the signal, it has broadcast a repeating buzzing noise. Every few years, the buzzer stops, and a Russian voice reads a mixture of numbers and Russian names.

A typical message came hours before Christmas day, 1997:

“Ya UVB-76, Ya UVB-76. 180 08 BROMAL 74 27 99 14. Boris, Roman, Olga, Mikhail, Anna, Larisa. 7 4 2 7 9 9 1 4”

Instead of shutting down with the fall of communism in Russia, UVB-76 became even more active. Since the millennium, voice messages have become more and more frequent.

It’s easy to dismiss the signal as pre-recorded, or a looping tone. But what listeners quickly realized was that UVB-76 is not a recording. The buzzer noise is generated manually. The reason for hearing telephone conversations and banging noises in the background of the signal is that a speaker creating the buzzer is constantly placed next to the microphone, giving the world an eerie insight into whatever cavern the signal originates from.

The modern popularity of UVB-76 can be traced to /x/, 4chan’s non-archiving message board devoted to discussion of paranormal activity and unexplained mysteries. Just as 4chan created memes like Pedobear and Rickrolling, the online image board served to bring UVB-76 before the eyes of a host of Internet users.

Online chatter about the signal increased in 2010 as bizarre broadcasts were issued on an almost monthly basis. Snippets of Swan Lake were played, a female voiced counted from one to nine, a question mark was transmitted in Morse code, and strange telephone conversations were overheard by the receiver.

Since October 2010, the station has changed location. The flurry of activity and voice messages preceded the most important development in the signal since it began broadcasting in the 1970s. It seems likely that the heightened activity of 2010 was related to the establishment of the signal in a new location. The new call sign was read out after the move: “MDZhB”.

Previous triangulation efforts had led to the discovery of the transmitter for UVB-76: a Russian military base on the outskirts of Povarovo, a small town 19 miles from Moscow.

After the station changed location, two groups of urban explorers and UVB-76 followers travelled to the remote Russian town in an attempt to visit the military bunker that the signal had originated from for over 30 years. When they reached the town, a local man told them about the storm of 2010. One night a dense fog rolled in, and the military outpost was evacuated within 90 minutes.

After making their way across the site and avoiding the guard dog stationed outside, the groups found the bunker and military buildings in a state of abandonment. Possessions and equipment were strewn across the base. Icy water had filled the bunker, yet clues were still to be found inside. One group described the Povarov military bunker as “a quiet and lonely dark place, something like a maze with lots of corridors and rooms.”

A book was found that contained a log of messages sent by UVB-76. The ethereal signal that had fascinated the world for years now had a physical presence, along with confirmation that it had been run by the Russian military.

But the mystery continues to this day. Sporadic voice messages are still emitted. Legions of listeners tune in via radios and online streams every day. A file can be downloaded at this link that allows followers to listen to UVB-76 in iTunes.

Along with a renewed interest in studying and archiving the broadcasts of UVB-76, multiple triangulation attempts have been made to try and ascertain the new location of the signal. Unlike before, it seems that UVB-76 is emanating from multiple transmitters across Russia. Triangulation has given rise to three possible locations.

One possible location is the small Russian village of Kirsino, which has a registered populace of just 39 people. One signal can be traced here. But this isn’t the fan-favorite location.

Near to the Estonian border lies the Pskov Oblast. This is currently the most likely source of UVB-76, due to the multiple triangulation attempts that lead here.