From Signal Identification Wiki
RDL is one of the most interesting VLFVery Low Frequency (3-30 kHz) stations due to its variety of modes and intermittent, but frequent operation.
The station has two modes of operation:
- Fast FSKFrequency-Shift Keying, used most of the time
- Slow Morse FSKFrequency-Shift Keying, cleartext. Usually broadcasts the callsign, followed by some numbers, and finishing with the time of the transmission.
The transmissions will cease, or switch to a very low power when the message is sent. The duration of the transmission is very variable, from less than a minute to more than ten.
When in CWContinuous Wave-FSKFrequency-Shift Keying mode: