[Aavso-sid-list] Unidentifiable Signals at VLF

[pws]

Dear fellow observers,

Merry Christmas and - looking foreward - a Happy New Year 2008!

I'm observing two VLF-traces at 21.4 and (very faint) at 22.8 KHz.
Both are showing reliable diurnal variation. 21.4 seems to be NPM coming 
in via the magnetic North Pole from here, approx. 12000km/350°.

Anybody out there who could give me a hint what kind of signal I`m 
receiving on 22.8 KHz? NWC, Australia is known to be "Not Active".
Example: http://home.arcor.de/df3lp/spec/img/07-12-29.png

Greetings from Europe,
Peter