The broadcast has been carried twice a day on the shortwave frequency since the beginning of the US-Israeli attack on Iran on February 28.
According to PRIOM, an organization that tracks and analyzes global military and intelligence use of shortwave radio, using established radio-location techniques, the broadcast was first heard when the US bombing of Iran began. Since then it has run like clockwork on the 7910 kHz shortwave frequency – at 02.00 UTC and again at 18.00 UTC.
Over the weekend, Priyam said it had identified the possible source of transmission. Using multilateral and triangulation techniques, the group traced the signal to a shortwave transmission facility inside a U.S. military base in Böblingen, southwest of Stuttgart, Germany.
The site is located in a restricted training area between the Panzer Kaserne and Patch Barracks, with technical operations possibly involving the US Army’s 52nd Strategic Signal Battalion, headquartered nearby.
That detection limits the scope, but it does not reveal who is behind the broadcasts or who they are for.
The broadcast, lasting two hours, is divided into five to six segments, each lasting 20 minutes. Each begins with “Attention!” It happens from. Before being transferred to a series of numbers in Persian, sometimes punctuated with an English word or two. Five days after the broadcast, radio jammers were heard attempting to block the frequency. The next day, transmission shifted to a different frequency—7842 kHz.
Radio communications experts believe the transmission is likely part of a Cold War-era system known as a number station.
return of numbers
Number stations are shortwave radio broadcasts that play strings of numbers or codes that sound random – such as those 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 armies,” says Maris Goldmanis, a Latvian historian and avid researcher of number stations.
Number stations are commonly associated with espionage. “For intelligence agencies, it is important to communicate with their spies to gather intelligence,” says John Siefer, a former US intelligence officer who served for 28 years in the CIA’s National Secret Service. “That’s not always possible in person because of political constraints or conflict. That’s where the numbers stations come in.”
While the use of number stations can be traced back to World War I, they came to prominence during the US–Soviet Cold War. Goldmanis says that as espionage became more sophisticated, governments used automated voice transmission of coded numbers to communicate with agents. Citing declassified KGB and CIA documents, he said that number stations were widely used during this period, often in the form of 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,” says Siefer. “But during the Cold War and even before, governments had to find ways to do this without being noticed, and transmitting coded messages was a way to secretly communicate with your assets.”
The apparent randomness of the numbers means they can only be deciphered from a codebook, says Cipher. He says, “Unless you have a codebook that can give you hints on how to decrypt the code, no one can make heads or tails of it or understand what it says.” He said such systems should already be established and coordinated.
a signal without a sender
Although the possible origin of the signal may now be clear, its purpose and intended recipient remain unknown.
Goldmanis says that because transmissions are encrypted and designed to be secret, those details may remain obscure for years. The structured nature of the transmission – its fixed schedule and frequent use of frequencies – further suggests that it is part of a planned operation.
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