“Tavajoh! Tavajoh! Tavajoh!” a man’s voice announces, before going on to narrate a string of numbers in no apparent order, slowly and rhythmically. After nearly two hours, the calls of “Attention!” in Persian stop, only to resume again hours later.
The broadcast has been playing twice a day on a shortwave frequency since the start of the US-Israel attack on Iran on February 28.
According to Priyom, an organization which tracks and analyses global military and intelligence use of shortwave radio, using established radio-location techniques, the broadcast was first heard as the US bombing of Iran began. It has since played on the 7910 kHz shortwave frequency like clockwork—at 02.00 UTC and again at 18.00 UTC.
Over the weekend, Priyom said it had identified the likely origin of the broadcast. Using multilateration and triangulation techniques, the group traced the signal to a shortwave transmission facility inside a US military base in Böblingen, southwest of Stuttgart, Germany.
The site lies within a restricted training area between Panzer Kaserne and Patch Barracks, with technical operations possibly linked to the US army’s 52nd Strategic Signal Battalion, headquartered nearby.
That identification narrows the field, but it does not reveal who is behind the transmissions or who they are meant for.
The two-hour-long transmission is divided into five to six segments, each lasting up to 20 minutes. Each opens with “Tavajoh!” before shifting into a string of numbers in Persian, sometimes punctuated with an English word or two. Five days into the broadcast, radio jammers were heard attempting to block the frequency. The following day, the transmission shifted to a different frequency—7842 kHz.
Radio communication experts believe the broadcast is likely part of a Cold War–era system known as number stations.
The Return of the Numbers
Number stations are shortwave radio broadcasts that play strings of numbers or codes that sound random—like the one now heard in Iran. “It is an encrypted radio message used by foreign intelligence services, often as part of a complex operation by intelligence agencies and militaries,” says Maris Goldmanis, a Latvian historian and avid numbers stations researcher.
Number stations are most commonly associated with espionage. “For intelligence agencies, it is important to communicate with their spies to gather intelligence,” says John Sipher, a former US intelligence officer who served 28 years in the CIA’s National Clandestine Service. “This is not always possible in person due to political constraints or conflict. This is where number stations come in.”
While the use of number stations can be traced back to the First World War, they gained prominence during the US-Soviet Cold War. As espionage grew more sophisticated, governments used automated voice transmissions of coded numbers to communicate with agents, Goldmanis says. Citing declassified KGB and CIA documents, he adds that number stations were widely used during this period, often as Morse code transmissions and, in many cases, as two-way communications, with agents reporting back using their own shortwave transmitters.
“Nowadays, you have various satellite and encrypted communications technologies,” Sipher says. “But during the Cold War and even before that, governments had to find ways to do this without being noticed, and broadcasting coded messages was one way to communicate with your assets discreetly.”
The apparent randomness of the numbers means they can be understood only with a codebook, Sipher adds. “Nobody can make heads or tails of it or understand what it says unless you have the codebook that can give you hints to decrypt the code,” he says, noting that such systems must be set up and coordinated in advance.
A Signal Without a Sender
While the likely origin of the signal may now be clearer, its purpose and intended recipient remain unknown.
Because the broadcasts are encrypted and designed to be covert, those details may remain unclear for years, Goldmanis says. The structured nature of the transmission—its fixed schedule and consistent use of frequencies—further suggests it is part of a planned operation.
One theory is that the broadcasts originate from Iran itself, as part of its wartime intelligence efforts—particularly if traditional covert communication channels have been disrupted. “Such a station would have appeared if the Iranian intelligence service had lost its usual way of covert communication with the Iranian agents abroad because of the Israeli and US strikes and was now required to use a shortwave radio to send messages and instructions,” he says.
However, another more widely backed theory is that perhaps the US, Israel, or an Iranian opposition group in exile that is based in Europe is using shortwave transmitters to reach allies inside. “There is also a suggestion that these broadcasts are used to confuse and distract the Iranian security,” Goldmanis adds.
Meanwhile, just days after the first broadcast, attempts to jam the signal began. Since March 4, onlookers have observed interference consistent with a technique known as a “bubble jammer,” a method previously associated with the Iranian regime.
“Iran has used these bubble-like sounds to jam Radio Farda, Voice of Israel, Voice of America in the past, and this suggests that Iranian security is aware of these broadcasts and wanted to disrupt them,” Goldmanis says, adding that this lends some credence to the theory that the source of the broadcast may be someone opposed to the Iranian regime.
The station also responded, switching frequency to avoid the interference, he says.
Why Now?
Number stations have captured the imagination of academics and conspiracy theorists alike for decades, with dedicated forums and online communities trying to make sense of the few remaining broadcasts.
The emergence of a new station at the cusp of a major geopolitical event has energized that community. “The appearance of a new numbers station should be viewed as an extraordinary event, because of all the other numerous ways of covert communication,” Goldmanis says.
Even so, the system itself is clunky, Sipher says, “involving equipment and headphones, and a person at the other end receiving the numbers, writing them down, and then using the codebook to understand the message.”
“With the technology available today, this is a communication mechanism of the last resort,” he adds.
Since the start of the US-Israel attacks, the Iranian government has clamped down on internet access, with blackouts across the country lasting up to 500 hours. “We have seen in recent times what happens in Iran when the internet experiences a complete shutdown, when secure applications like Telegram are completely blocked in Russia, or access to Starlink is lost,” Goldmanis says.
In such scenarios, old-school methods like shortwave radio might seem like a reliable source for covert communications. “Shortwaves can be received over large distances, and all you need is a technically valid shortwave radio and a location free from interference,” he says.
While radio is unlikely to replace modern technologies during wartime, unique circumstances can force a return to analog tools. Sipher says such systems are harder to trace. “It’s useful because there’s no way for the Iranian regime to figure out who is receiving the incoming signals, because it is being broadcast to everyone. It is unlike a Starlink device receiving internet and can be located; there’s no way to determine who’s listening in to the numbers.”
The station appeared at the start of the war—and while key questions remain, its timing, structure, and suspected origin point to an intelligence operation unfolding in real time.
This story was originally published on WIRED Middle East.
