UVB-76 (sometimes referred to as UZB-76, but recently MDZhB, as of Sep. 9th, 2011, the feed changed its call letters again to "94ZhT") is the call sign of a shortwave radio station that usually broadcasts on the frequency 4625 kHz (AM suppressed lower sideband). It features a short, monotonous About this sound buzz tone, repeating at a rate of approximately 25 tones per minute, for 24 hours per da
y. 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. The station transmits a buzzing sound that lasts 1.2 seconds, pausing for 1–1.3 seconds, and repeating 21–34 times per minute. Until November 2010, the buzz tones lasted approximately 0.8 seconds each. One minute before the hour, the repeating tone was previously replaced by a continuous, uninterrupted alternating tone, which continued for one minute until the short repeating buzz resumed, although this no longer occurs. The Buzzer has apparently been broadcasting since at least 1982 as a repeating two-second pip, changing to a buzzer in early 1990. It briefly changed to a higher tone of longer duration (approximately 20 tones per minute) on January 16, 2003, but it has since reverted to the previous tone pattern. Frequently, distant conversations and other background noises can be heard behind the buzzer, suggesting that the buzz tones come from a device placed behind a live and constantly open microphone (rather than a recording or automated sound being fed through playback equipment), or that a microphone may have been turned on accidentally. One such occasion was on November 3, 2001, when a conversation in Russian was heard: "Я — 143. Не получаю генератор." "Идёт такая работа от аппаратной." Not receiving the generator (oscillator)." "That stuff comes from hardware room."). Voice messages for UVB-76 were believed to have been very rare until a sudden spate of activity in the latter half of 2010. They are usually given in Russian by a live voice and repeated. At least seven such messages have been heard in over twenty years of (non-continuous) observation. 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 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 and morse code messages.
