Sorry, 
the German text was meant to be send as a 
private mail. 
Anyway now that it's here the translation:

Do you talk about the 100 Hz 'fence' ?
This is common in VLF at various frequencies. 
I still don't know of a proper explanation. 
Related to the power grid ...


Normally I*m a lurker here and read vlf messages. 
More active contribution in Yahoo vlfgroup, 

ma apologies, 

Walter