Possible Russian Marker 'Airhorn' 4020kHz
This signal was discovered in the past week or so on uTwente's webSDR. This signal features a constant airhorn-like sound that is repeated. The sound is roughly .5 seconds with a .6 second pause. The signal also has a suppressed lower side-band, which is a feature on the Buzzer, and shares this characteristic with the Squeaky Wheel and Pip stations. I checked other SDR's that can tune to this frequency and it is best heard on Poland's SDR. Periodically, a RTTYRadio TeleTYpe source appears at 4020 kHzKiloHertz (kHz) 10^3 Hz, but through some research, the RTTYRadio TeleTYpe signal is not part of the broadcast signal.
After about a month of silence on the 4020 frequency, on December 25th, 2018 the Airhorn was picked up with a weak signal on the UTwente WebSDR File:websdr_recording_start_2018-12-29T23_45_50Z_4020.0kHz (mp3cut.net).mp3 File:websdr_recording_2018-12-30T01_40_43Z_4020.0kHz (mp3cut.net).mp3