UVB76 (MDZhB) is the call sign of a shortwave radio station that usually broadcasts on the frequency 4625 kHz (AM suppressed lower sideband). It is known among English speaking radio listeners by the nickname The Buzzer. It features a short, monotonous buzz tone, repeating at a rate of approximately 25 tones per minute, for 24 hours per day. The station has been observed since around 1982. On rare occasions, the buzzer signal is interrupted and a voice transmission in Russian takes place. Despite much speculation, the actual purpose of this station remains unknown to the public.
There is much speculation about the current transmitter site. The former transmitter was located near Povarovo, Russia at 56°5′0″N 37°6′37″E which is about halfway between Zelenograd and Solnechnogorsk and 40 kilometres (25 mi) northwest of Moscow, near the village of Lozhki. The location and callsign were unknown until the first known voice broadcast of 1997. In September 2010, the station's transmitter was moved to near the town of Pskov. This may have been due to a reorganization of the Russian military.
The purpose of UVB-76 has not been confirmed by government or broadcast officials. However, the former Minister of Communications and Informatics of the Republic of Lithuania has written that the purpose of the voice messages is to confirm that operators at receiving stations are alert. Another theory concerns an article published in the Russian Journal of Earth Sciences which describes an observatory measuring changes in the ionosphere by broadcasting a signal at 4625 kHz, the same as UVB-76. However, this would not explain the voice or morse code messages. In 2011 a group of urban explorers explored the abandoned buildings at Povarovo. They claim that it is an abandoned military base. A radio log record was found. It is likely that voice messages are some sort of Russian military communications. Other claims are that the broadcast is constantly being listened to by military commissariats.