Enigma ID M04
Frequencies 5748, 7250, 8188
Status Inactive
Voice N/A
Emission mode MCW
Location Poland
Activity pages

M04 was most recently operated by the Polish Office for State Protection (UOP). It was a Morse code counterpart to G02, and later E23. Last heard on 14 September 2000.[1]

The traffic format is given below. The speed was 19 words per minute. Standard five dashes were used for zero.

Preamble Message Outro
U LOLO LOLO LOLO / 01723 LOLO / 01723 BT BT 89261 12616 ... 31657 AR SK
Tuning signal 5-figure message header 5-figure message header   Fixed-length message of 100 5-figure single groups  
Repeated for 3 minutes Repeated for 5 minutes Repeated twice Repeated twice

Full transmissions always took roughly 26 minutes.


Prior to April 1998, M04 used the following schedule.[2] The counting of the weeks started on the first Saturday of the month.

Day UTC Freq Week 1 Week 2 Week 3 Week 4 Week 5
Monday 20:00 5340     x    
Tuesday 18:00 4195 x        
Tuesday 20:00 4195 x x      
Wednesday 09:00 4195   x      
Thursday 20:00 5340     x    
Thursday 21:00 5340     x    
Friday 00:00 5340       x  

The U's at the beginning were initially repeated for 10 minutes. In April 1998, it was shortened to 3 minutes.

On 1 April 1998, the schedules above were replaced, and the following schedules came into use.[3] The transmissions from now on only took place on the second Monday, Wednesday and Thursday, with the same message repeated throughout all the transmissions during the week.[4] The counting of the weeks still started on the first Saturday of the month.

Monday, Wednesday, Thursday
Week 09:57 11:57 12:57
2nd 7250 8188 5748

The final M04 transmission was on 14 September 2000, however, blank carriers were transmitted for the length of E23 transmissions on its former schedules until 2002.[1]


  1. Numbers & Oddities #32 (December 2000) [accessed September 13th, 2014]
  2. ENIGMA Newsletter #10 (January 1996), p. 7-8 - read a scanned version here
  3. Simon Mason, G2/E23 [accessed September 13th, 2014]
  4. Numbers & Oddities #8 (December 1998) [accessed September 13th, 2014]

Recording courtesy of Numbers & Oddities