HM01: the Cuban numbers station that sends voice and data on 11530 kHz

What you hear

A woman's voice in Spanish reads groups of five digits, slowly and clearly, in the mechanical cadence of a recording assembled from single spoken numbers. After a group or a few groups comes something no other numbers station does: a burst of digital noise, a few seconds of modem-like screech, and then the voice again. Voice, data, voice, data, through the whole transmission. Listeners who looked at the bursts found a known amateur data mode inside them, of the kind used to send small files over shortwave, and that gave the station its description: a hybrid that sends the agent both the spoken groups and a file.

HM01 was famous for its slips. Operators started transmissions late, sent the wrong part at the wrong time, left the transmitter on between schedules, and once in a while other audio leaked into the transmission. For a station whose purpose depends on anonymity, it was oddly human, and that is exactly why listeners grew fond of it.

Since 23 August 2024 the station has been off the air. The catalogue records a transmitter failure as the reason and leaves the entry in place because it may return.

Who transmits and why

The station is attributed to Cuba, and unlike most numbers stations the attribution rests on more than guesswork: its predecessors were tied to Cuba by direction-finding over many years, and in espionage cases in the United States Cuban number broadcasts figured in the evidence. The purpose is the usual one: to pass instructions to people abroad who need nothing more incriminating than a shortwave radio to receive them, encoded with a one-time pad that cannot be broken without the key. The data bursts presumably carry the same kind of content in another form; what any of it says is not known. Cuba has never acknowledged the station.

Everything goes out in the clear for anyone to receive, and receiving is all a listener does.

When and where to listen

HM01 worked to a schedule by the hour, moving between frequencies through the day. The catalogue lists 9065, 9155, 9240, 9330, 10345, 10715, 10860, 11435, 11462, 11530, 11635, 12180, 13435, 14375, 16180 and 17480 kHz. Listen from the Americas first: receivers in Florida, the Caribbean and the eastern United States heard the station at great strength, and Central and South America well too. From Europe the lower frequencies in the list reached across the Atlantic in the European evening and night when conditions allowed.

The transmission was AM, and the program sets AM, which is right for the voice and lets the data bursts through unchanged. If the station comes back and a nearby signal interferes, switching to the sideband away from the interference is the usual remedy. Until then, the frequencies are worth an occasional check: a carrier appearing on one of them at the top of an hour would be the first sign of a return.

In ShackDeck

Station catalogue → Mystery stations → HM01 Cuba 11530. The program picks a public receiver that covers 11530 kHz, tunes it and sets AM; no receiver, antenna or account of your own is needed. An empty frequency is the expected result for now, so a receiver in the Americas and a glance at the other frequencies in the list are the way to check whether anything has changed.