Hi Gerhard well those a pretty :-)) and very like space invaders! I have
never seen anything quite like that. I would suggest they are an effect from
a local source. If you dont mind I would like to throw that plot at the VLF
group who are quite knowledgable about manmade sources. Renato Romero has
done a lot of detective work to pin some of those kind of strange effects
down at below 24kHz.

 They seem too regular for "motor-starts" but could possibly be the
harmonics of something like that locally. You will have to quiz the local
"Home Improver" hobbists as to when they have been using their drills :-))
or rush outdoors and see if you can hear any sound lasting around minute (I
think that is the duration.)

Alan G3NYK

----- Original Message ----- 
From: "Gerhard Hickl" <[email protected]>
To: <[email protected]>
Sent: Monday, September 27, 2010 6:13 PM
Subject: LF: Aliens on LF !


> Hello Group!
>
> Has anybody an explanation for the kind of signals displayed on my
> grabber sometimes?
>
> They appear not periodically but rather random but always around 137720.
> I noticed them first a few month ago in spring.
>
> I think it is caused by an electrically device locally but which kind of
> stuff could do this signal?
>
> Any ideas?
>
> 73 es gl
>
> OE3GHB
> Gerhard
>
>