Strange VLF signals

Allan Isaacs

I raised my wire antenna with the aid of a home made bow and arrow and some trees so its now 50 feet high and about 500 feet long.
Apart from various noisy power supplies I can see quite a few real signals which were previously weak.
I think I can identify a Norwegian transmission at 16.4KHz, but just LF of it there is a broadband transmission, or maybe local interference, that seems to have three modes.
A spread of carriers about 100Hz apart... attached
A narrower spread, much weaker
And off for varying periods.... attached
Is this some sort of ionosphere monitoring system or something more mundane?
Allan G3PIY

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