XPB is a recently discovered digital numbers station operated by the SVR. First noted in 2014, this station uses a 16-tone MFSK modem at a 65.79 Bd rate. The tones are spaced by 175 Hz, ranging from 540 Hz to 3165 Hz. The station structure consists of a test tone emitted 10 minutes before the transmission. Then the message is sent. A beginning tone like XPA or XPA2 is not present in a message.
The transmitter site is presumed to be located near Moscow, Russia. XPB had originally undergone a lot of testing from 2014 until mid 2018 and was never given an ID. Over this time, they tested different baud rates and waveforms. The station was tested transmitting at 16.45, 32.89, 65.79, and 131.58 (approx.) Bd rates. Test transmissions were usually sent out every 20 minutes or so for a few hours.
Recording Sample (2022, 66 Bd Rate)
On May 17th, 2021 XPB started using a new Serdolik waveform system. It went on for about 1m 14s then the usual MFSK-16 transmission started.
Serdolik Waveform Recording (Source: N&O)
Schedule
The first stable XPB schedules were observed around mid 2018 after the long periods of testing described above. XPB transmits twice weekly, and sends 6 of the same transmissions 10 minutes apart. Each successive transmission is about 1-2 MHz lower or higher in frequency. Schedules usually change every month.
Numbers Station Summary
Enigma ID: XPB, XPB1
Activity: Active
Emission Mode: USB, 16-tone MFSK 66Bd
Believed Country of Origin: Russia
Related Stations: E07, G07, S07, V07, M12, XP, XPA, XPA
Sources
Enigma 2000 Newsletter Issue #112, Page 2
Numbers and Oddities Edition #259 (2019), Page 45
Numbers and Oddities Edition #284 (May 2021), Page 93