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Date: Fri, 28 May 2010 18:26:54 +0200
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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Subject: VLF: 8.97kHz - Near field and radiated signals, and all the nice
 experiments :-)
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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