Thanks to K2ORS for bringing the transmission to the attention of the group.
It gave me a project to play with over the weekend.
I used a 60KHz MSF ferrite rod receiver and tuned it down to 17.2KHz.
Then piped it into Spectrum Lab. Placed it in the upstairs window and
switched everything off in the house except the PC.
This morning's transmission was 40dB over the noise, and the afternoon was
about the same peak level, but with 10dB more QRM lifting the noise floor.
Fascinating to hear the break -20dB from the key down carrier. As well as
the drift's in frequency. I would have though that it would have drifted LF
on key down and returned back HF, but it appeared to be the opposite.
Fun seeing TV line timebase on 15.625KHz too, they were all off in the area
Harrogate, N Yorkshire IO93gx