Jacek, very interesting!
So, it is worth to do a test with a large earth electrode antenna and
moderate power (100W...500W) and a E field antenna. I would give a loop
antenna a try too, as long as it is a quiet location. With such antennas
(without HV and space limitations) one could do some nice long time tests!
Horst, go out! (hi).
Maybe there can be reached much more than we all currently belive. It's
time that someone tries that :-)
Will be interesting results.
Today i improved my 2nd grabber very very much. The IM is gone and DHO38
apperas with up to 40dB above noise (with NB). The band is almost clean
of local QRM lines, at least in the 8,97+-0,02 kHz sector. All in all it
is the best S/N i reached until now at this location in the 7th floor. I
will go on improving but now it makes sense to do a test transmission
from that 1,8km distanced QTH :-) Maybe i will do that this evening
(depending on the WX) :-)
The improvement is caused by a series resistor between wire and gate of
the first stage (1MOhm). TNX to Ha-Jo, DJ1ZB for the conviction! The R
forms a low pass filter together with the gate capacity (-3dB @ abt 50
kHz). Thus, the strong LF and MF broadcast signals are well attenuated,
as it seems. I am interested what happens in the night, when QRM goes
down and the LF/MF DX window opens. The grabber2 is still available at
http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html
Dear dreamers, wish you fun and motivation for your tests :-)
73, Stefan/DK7FC
Am 28.05.2010 14:24, schrieb Jacek Lipkowski:
On Wed, 26 May 2010, Roger Lapthorn wrote:
- What antenna did you use for RX? Loop, e-field probe?
i used an e-field probe
- Have you tried TXing using grounded electrodes? If so, what range
did
you achieve and what RX antenna did you use?
i've tried to couple to various structures (underground wires etc),
one of them worked like a ground dipole. i got around 750m with 1.8W:
http://acid.ch.pw.edu.pl/~sq5bpf/ham/vlf/20100203/vlfcapt3747.jpg this
was in february, during summer the distance would have been smaller.
this is from a bit shorter distance, around 570m:
http://acid.ch.pw.edu.pl/~sq5bpf/ham/vlf/20100203/vlfcapt3744.jpg i
have tried using 40W into a 1.5x2.5m 3 turn loop - in this case there
was marginal copy at the same location (can't find the spectrogram
unfortunately). as you can see in this case it's much better than
marginal.
i've used a loop for both tests. i've tried the location 1.3km away
(that was not a problem for e-field antennas), but didin't receive
anything. actually i would be surprised to receive something at 1.3km,
it it was marginal with half of this distance. so you can see that at
least in my case the e-fields antenna clearly wins
btw performing these tests in the city is not just a matter of turning
on the tx and driving around. you have to search for quiet sites to
listen, and drive there.
jacek
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