Number Stations

Stations

Numbers on shortwave

Since the Cold War, shortwave stations have read out groups of digits for listeners nobody names. A few still do, and you can hear them tonight.

What they are

Five figures at a time

A numbers station broadcasts a voice, a tone or Morse reading groups of digits or letters, usually five at a time, on a fixed schedule. The usual explanation is one-time-pad messages to agents abroad: a shortwave set is easy to explain away, and nothing tells the sender who is listening.

Governments rarely admit to them, though spy trials in the United States have shown agents copying Cuban broadcasts.

Listeners log them and give them designators by language:

E
English
G
German
S
Slavic languages
V
other languages
M
Morse
X
everything else

The scheme comes from ENIGMA 2000’s newsletter, and Priyom keeps the logs and schedules.

The log

Stations to know

Two you can hear every day, and three that went quiet, which you can still hear in recordings.

  • S28 The Buzzer UVB-76

    A short, rough buzz about 25 times a minute, day and night. Now and then a man’s voice breaks in with a Russian message of names and numbers.

    On air 4625 kHz

  • S30 The Pip

    Short pips, about 50 a minute, around the clock, with the occasional message in Russian.

    On air 3756 by night, 5448 by day kHz

  • E03 Lincolnshire Poacher

    Bars of the English folk tune on a loop, then a woman’s voice reading five-figure groups. Thought to be British, broadcast from Cyprus.

    Off the air since 2008

  • E03a Cherry Ripe

    The Poacher’s format with a different tune, heard across Asia and Australia.

    Off the air since 2009

  • G02 Swedish Rhapsody

    A music box playing a phrase of Alfvén’s Swedish Rhapsody, then a child’s voice reading numbers in German.

    Off the air since 1998

Today’s schedules, on Priyom

No radio needed

Listen through a WebSDR

A WebSDR is a receiver someone shares on the web. Firefox has them bookmarked.

  1. Open Firefox from the dock and choose the WebSDR bookmark.
  2. Pick a receiver that covers shortwave, such as the University of Twente’s in the Netherlands.
  3. Type 4625 in its frequency box and choose AM.
  4. Wait for the buzz.

Priyom’s schedules are in UTC, and so is the clock in the top bar.

With a dongle

Down to shortwave with an RTL-SDR

Numbers stations live between about 3 and 20 MHz, below where a plain RTL-SDR tunes. There are two ways down.

Direct sampling. Some dongles, such as the RTL-SDR Blog V3, can sample HF directly. In Gqrx’s device settings, add direct_samp=2 to the device string:

Gqrx device string

rtl=0,direct_samp=2

An upconverter shifts HF up into the dongle’s range. Set Gqrx’s LNB LO to minus the converter’s offset, −125 MHz for the common 125 MHz kind.

Either way, give it a long wire, ten metres or more and as high as you can, then tune to 4625 kHz in AM.

Record and compare

Keep what you hear

Gqrx’s Rec button saves what you hear as a WAV file. Open it in Audacity and switch the track to its spectrogram view: the buzz, the pips and the voice show up as bands, the way they do on the waterfall.

The Conet Project, bookmarked in Firefox, is a 1997 collection of numbers-station recordings, free on the Internet Archive. It has the Poacher and the Rhapsody from when they were on the air.

In a terminal

# Or record from the terminal: one minute of the default input
rec -c 1 buzzer.wav trim 0 60

Listening and the law

Rules differ by country

Listening is legal in most places, though some countries forbid passing on what you hear when it was not meant for you. Check where you are. Transmitting is another matter: it needs a licence, and amateur rules forbid encoding a message to hide its meaning.

Before you transmit Download Number Stations