Hi VLF,
Today i've installed a second loop into the tree. It is a simple copper
tube having 10 mm diameter and about 4m length.
https://dl.dropboxusercontent.com/u/19882028/VLF/20160427_084708.jpg
The loop is not resonated. The ends are just hold together with a screw.
https://dl.dropboxusercontent.com/u/19882028/VLF/20160427_092012.jpg
It is a very stable / robust construction which needs no further
elements to hold it into the tree.
The screw is protected against rain with some bonding tape. Before the
mounting, a ferrite transformer with Al ~ 6000 nH was put on the tube.
First i tried 20 secondary turns.
https://dl.dropboxusercontent.com/u/19882028/VLF/20160427_092420.jpg
Later i choose 40 turns and finally 80 turns.
The results between the N-S loop and the E-W loop are still visible at
http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html
DHO38 is much weaker, the Alphas are much stronger, HWU is stronger.
All in all it appears that this loop performs better then my 80 turn
hula hup circle loop (0.8m diameter). And by using the transformer it
can be adapted optimally to the preamp input impedance. It even works
down to 100 Hz, with limited performance of course.
I'm now looking forward to receive something from the East or West. Is
there someone out there ready to radiate a signal?
Also, a VLF RDF grabber would be fine, maybe even by using idenetical
antennas (to be built).
73, Stefan
PS:
BEWARE: This is not new! Someone has done it before, maybe even in the
1920s. VLF receptions on the Dreamers Band were done with such a loop
for example by F5WK (http://f5wk.blogspot.de/2010/09/antenne-loop-vlf.html).
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