Letter from "Marcel"
I am amateur radio since 1975 and a short waves enthusiast since 30 years now. From 1977 to 1982, I was serving in the French Army in Germany as an electronic specialist. At home, I used at the moment a Yaesu FRG 7 receiver
with only an analogue display. Usually I calibrated the receiver display with 2 time stations : one located in Nauen DDR on 4.525 MHz and another one in Tchecoslovakia on 3.170 MHz.
While scanning the band, I found a number station on 3.820 MHz, starting transmissions every night at 21:00 local time. A few minutes before starting, the station identified by a repeated sequence of 4 musical notes, something like C, E, G, C.
At 21:00, a woman started to list numbers. After a short analysis, I found some explanations of the process. Here is an example of transmission
32456/03
16534/08
20087/10
12376/14
21354/19
32564/23
The first group is the identification of the receiver. The 2 digits after the slash correspond to the minutes after the hour when the transmission will start for the receiver.
Let's see now a message
At 21:14 the woman says two times
12376/21
That means the message will consist of 21 groups of five numbers. And she transmits (always two times) each group of 5 numbers. At 21:19, the process will be the same for the receiver 21354. Usually, the sequence ended around 21:30 and was repeated at 22:00.
As I had some friends working as operators on HF direction finding networks, I asked them to occasionally make a control on this mysterious 3820 phone signal.
A few days later, I received the bearings from the stations and I carefully plotted them on a map of Germany (West and East). The transmitter seemed to be located in the south-west area of Berlin (probably around 20 to 50 kms).
On operating near Paris. At his home, they found a Grundig Satellit 2000 receiver. This unit was equipped of a barrel to switch the SW bands. One band of the barrel was modified to a fixed frequency, in order for the agent to immediately pinpoint the number station from which he received his instructions.
And what about deciphering ? The same guy told me they usually used one time pads with groups of 5 random numbers. By superposing the 5 numbers groups from a sheet of the pad to the 5 numbers groups received by radio and adding the numbers digit by digit modulo 10 they could get a numerical equivalent of plain text.He told me too that, because many supposed spies were proved guilty when a one time pad was found at their home, some of them used special deciphering program running on a pocket calculator like the HP 67 at this time. The magnetic stripe for the program was easier to hide.
At last, engineers from a major German electronic company involved in electronic warfare told me not all the German numbers stations were in DDR, but some of them were in FRG working for BND (BundesNarichten Dienst = German intelligence agency) located in Pullach near Munich. This agency had a lot of agents on eastern side of the iron curtain.
Another tricky station to end : One day, during the same years, while typing 4525 (for Nauen time station) on the keyboard of a professional receiver, I did a mistake and typed 4625. There, a beep signal looking like a time station but giving a beep every around one and half second. The DF network gave me bearings locating the station in USSR, not to far from the Polish border in Byelorussia. I don't know if it's still active and for which purpose this station was. If anybody has information, they are welcome.
