OLX begins its transmissions by repeating VVV DE OLX in CW five minutes before each broadcast. If it is going to be a CW transmission, the callup will be sent in normal CW. If it is going to be a YL voice transmission, the callup will be in modulated CW (MCW). At the top of the hour, the OLX callup ceases, and a three digit number is sent three times along with BT 011 011, which is repeated for several minutes until the actual message groups are sent. The voice transmissions are the same but without the 011 part of the callup. It's unclear what 011 is used for, and no other number has ever been sent.
I first logged OLX on 15 April 1992 on 5301 kHz sending 5F groups in CW. It wasn't until the 29th of April that I heard the OLX callsign being repeated before the CW broadcast. At the time I wondered if it was a mistake, since numbers stations just DO NOT use ITU callsigns. Later that same day I heard it being sent again, this time in MCW which was followed by the YL/Czech voice. I knew then that it was no mistake. But who was OLX? Checking my references, I found that it was issued for a RTTY press station located in Prague. However, the frequencies in use were not the ITU-allocated frequencies assigned to that callsign. Why would a press service use encoded numbers sent in CW and voice? It was apparent that this callsign was being used for a different purpose.
To make matters even more intriguing, Simon Mason decided to write to the address listed for OLX and try to get a QSL. Sure enough, they did reply with a QSL card listing the frequencies used by the numbers stations! This is not your average, run-of-the-mill numbers station. Their address is Ministerstvo Vnitra CR, P.B. 21/SK, 170 34 Praha 7.
Why would a numbers station, in the business of transmitting secure messages to parties unknown, use an ITU-allocated callsign and answer QSL requests? Well, I say, why not? If the encoded number messages themselves are secure enough, it really shouldn't matter who knows who's operating what station. I'm willing to bet that most intelligence agencies know who's operating what stations anyhow. It's just that most agencies want to keep their operations as secret as possible. That would at least give some plausible deniability to a government if their numbers operation were comprimised. OLX confirmed what frequencies they were using, and that's all. No mention of who is operating the station or for what purpose. Which is to be expected.
I think another possibility lies with the fact that the Czech Statni Bezpecnost (Czech intelligence agency) operates the station that for years was known as "Bulgarian Betty." If they're operating this station, what do they need OLX for? Could it be possible that they are "renting out" OLX for use by other agencies?
OLX has been off the air since the 3rd of August 1996. According to ENIGMA, OLX was having transmitter problems during the week ending 2 August, and was off the air completely on the 3rd. This may be due to flooding at the transmitter site, as that part of Europe was experiencing bad floods at that time last year. Nobody has logged any transmissions since then. They were operating 23 hours a day on the following frequencies & times:
2300 - 0400 on 5301//9320//11416
0500 - 1600 on 8142//14977//18303
1700 - 2100 on 5301//9320//11416
It's worth a listen to these frequencies to see if they return to the air. I hope they do. I had been meaning to send off for a QSL, but kept putting it off. See what I get? If anyone hears this station, please let me know.
Next month, as previously promised, I'll go into detail about the station numbering system used by the ENIGMA newsletter. See you then.