Daily Recurrent Ladders in VLF

Following my previous publication at the link : 

http://air-radiorama.blogspot.it/2017/05/scalette-in-vlf.html

I have checked several days one of the scheme of the ladders that occurs every days starting with a similar pattern at : 7.00 - 9.00 and 11.00 UTC as in the spectrogram recorded in the VLF Observatory of Turin in Electric field  in real time at the link : http://www.sidmonitor.net/gallery/station.html 

The same was received in Kiel in Electric field 

The strange is that in Kiel on H field , only the 7.00 - 11.00 UTC patterns are received 

My personal remarks could suggests that : 

A) This patterns are broadcasted from three different locations

B) The second pattern lies in a direction where there is a null in the directivity  of the H sistem of the Kiel Observatory 

C) For some reasons this VLF signals are broadcasted in a " Frequency Hopping way " 

Further investigation will be recording and demodulating this signals .

Images from the Kiel Longwave Monitor at the links :

http://lf-radio.de/cgi-bin/ki/show_wf.cgi?date=17-06-29

http://lf-radio.de/cgi-bin/fh/show_wf.cgi?date=17-06-29

and published under permission of : 

Peter Wilhelm Schnoor

Kiel Longwave Monitor

http://www.df3lp.de/