G04 – Three Note Oddity Numbers Station

G04, known as “Three Note Oddity” was a numbers station believed to be operated by Hungarian intelligence.  It’s frequencies indicate its operations were most likely restricted to Europe.  It was a very routine and stable station that had remained mostly unchanged since the height of the cold war.

It’s German language and routine European operations meant it’s target was most likely Germany.  The transmitter site was believed to be located out Budapest, Hungary.  Transmissions usually had a loud hum that made the quality very poor.  The station went inactive in 2005.

The voice it used was described as G03‘s voice, meaning it was another German numbers station that was generated by the Stasi Sprach Morse Machine.

Strangely, there was no message group count included in the preamble.  G04 transmitted highly non-random messages up until 2000.  It originally sent identical message groups that appeared two or three times in the same message.  There were also many groups that contained the same last 3 digits.

In 2000, the cryptographic method likely changed since these seemingly non-random messages were no longer observed.  The messages no longer contained any matching groups, or groups that had the same last 3 digits.  They also had no 9’s included in them, and no groups began with a 0.


G04 transmitted on two different frequencies every first Sunday of the month at 20:05 and 20:35 UTC, the latter transmissions time being 100 kHz higher.  During the winter the times changed to 21:05 and 21:35 UTC.  The same transmission eventually repeated on Thursdays at the same times and frequencies.

In April of 2000, the 2nd transmission began transmitting 100 kHz lower in frequency.  Frequencies changed slightly every month and ranged from 3127 kHz up to 5840 kHz.

3 Note Oddity Sample Version 1

3 Note Oddity Sample Version 2

Message Structure

Preamble Message Outro
*Three Rising Tones* *Pause Before Announcement* Achtung Achtung 87004 87004
25631 25631 …
Ende Ende
Interval signal Attention Attention 5-Digit paired
message groups
Repeats for 5 minutes


Numbers Station Summary

Nickname: Three Note Oddity
Emission mode:
Voice Summary:
Female and described as having the same voice as G03. Thus this station used the manipulated voice from the Stasi machine.
Believed Country of Origin:
Budapest, Hungary (Possibly)
Counterpart Station: M29
Station Family:
Family 13 “Three Note Oddity”


Simon Mason’s Website G4 Page
Numbers & Oddities Issue #18
Numbers & Oddities Issue #22
Recordings Obtained from Swldxer