Hi David,
Sorry for my late reply about your beverage antenna mail.
Thanks for your point of view to the beverage antennas and the
pictures. That sounds all very interesting and i can imagine about the
high signal levels coming from such a antenna. The problem in Germany
is o find a place which is far away from man made noise sources and
allow to hung up such a long wire.
But i have found such a place! :-) However i didn't spend much time and
interest to it regarding receive possibilities. I'm just getting
re-inspired by thinking of it. It is in a very quiet location!
In the forest of Heidelberg in JN49IK77 i hung up a 700m long wire. It
is called my earth antenna. The main intention is and was to transmit
on VLF on this antenna. The far end is grounded by 20 or 30 earth rods,
40cm deep and about 1m separated. The same on the other end. This forms
a loop where the current flows back through the earth. The lower the
frequency and the lower the ground conductivity, the deeper the return
path of the current, so the bigger the cross section area and the
higher the efficiency.
That region is a hill/mountain about 500m ASL and 400m above the local
ground in some km distance. The ground is out of stone with a layer of
soil, about 30cm. The need for a poor ground conductivity stands in
opposite to the wanted low loop resistance, which means the need for
high effort on the grounding at each end, i.e. a high number of ground
rods. Also the wire length is very important.
Anyway the efficiency will be poor but anyway you have a most seldom
and interesting transmit antenna whioch is
not
resonated, thus it is possible to transmit on any frequency. I'm also
looking forward to the 500 kHz allocation. It will be nice to use it as
a receive and transmit antenna on 475 kHz.
In summer when it is dry i achieved a loop resistance arround 800 Ohm,
which is coming from the grounding losses dominantly. I've done several
transmit tests and achieved 35 dB S/N in 4.5 mHz in a distance of 5 km,
to my own VLF grabber.
During the first times where the antenna was still shorter a wrote a
short report with some pictures:
http://dl.dropbox.com/u/19882028/VLF/VLF_5km_with_an_earth_antenna.pdf
Tests with Michael Oexner (SWL, NDB hunter) in 49 km were positive too,
in DFCW-600, see the attached Mail from 2010. BTW this is a VERY good
demonstration of the positive effect of band limiting, clipping and
noise blanking of the VLF signals processed in SpecLab. The picture
shown my signal with and without the SpecLabs noise reduction technics.
This 49km distance in 4.5 mHz is the current record with an earth
antenna. The transmit power was 200...250 watts if i remember correctly.
I will check if the antenna still exists and will refurbish it. Also i
will do new tests there. BTW i've done a recording on VLF using this
antenna in January, 29th 2011, if someone wants to play with it (1 GB):
http://dl.dropbox.com/u/19882028/VLF/29012011_12UTC_earth%20antenna_recording.WAV
In VK it seems you can easily arrange such an antenna, maybe even
across a stony hill and grounded into the sea at one end. You just need
some wire and a portable PA :-) BTW this is the PA i was using:
http://www.iup.uni-heidelberg.de/schaefer_vlf/12V_300W_VLF_PA.pdf
73, Stefan/DK7FC
