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Date: Thu, 23 Jun 2016 14:03:09 +0200
From: DK7FC <selberdenken@posteo.de>
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To: Renato Romero <contact@vlf.it>
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Subject: LF: Re: Cumiana OOS
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Status: O

BTW, i am now preparing for first tests on ULF, the range between 0.3 
... 3 kHz. Tests on 2970 Hz have started. This is a completely new 
league. 2970 Hz is almost 100x 'harder' than 8270 Hz. It is not easy to 
generate a high voltage on my wire on that frequency. Transformers 
saturate and i need 6.1 H of inductance! As a first step i am using a 
large ferrite transformer with 2 E cores and a coil body. I have wounnd 
3000 turns on it by hand! :-) The ferrite material is N27 and it can 
handle 1V / turn at 2970 Hz without a problem. I took 0.22 mm diameter 
wire. 15+ layers and each one is isolated by Kapton insulation tape, 
like the old TV transformers :-) See 
https://dl.dropboxusercontent.com/u/19882028/VLF/ULF%20loading%20coil%206.1H.jpg 
and 
https://dl.dropboxusercontent.com/u/19882028/VLF/6.1H%20ULF%20loading%20coil.jpg
I can run just 3 kV, not more. Otherwise the 'transformer' which is just 
a coil in fact, is risked to flash over.
At 3 kV my ERP is about 100 nW!
So far i managed 3.5 km to my own remote grabber, you still can see the 
last races at 
http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html. 
You still can see last traces from a previous 2 kV test there. The SNR 
was 25 dB in 424 uHz. But this is just a near field test... The far 
field starts at 16 km distance. It is a hard way to get that distance. 
But i have built a portable E field probe and stereo audio recorder with 
a Raspberry Pi. So i can take a walk in the forest and receive in really 
quiet places, far away from any electricity. My next plan i to receive 
my own signal in 7.9 km distance, there is a nice place :-) I have also 
ordered a second cheap Neo 6M GPS module for pps and NMEA signals on the 
other channel during the /p experiment. Then this will be a ideal 
portable monitoring system for post processing with absolute time stamps 
and even location informations are stored.
We will see. I'll come back to you when i think there could be a chance 
to see a trace on 2970 Hz, maybe in a 1 uHz BW :-) The QRN is MUCH lower 
there, relative to 8.27 or 6.47 kHz! Maybe this is an advantage that we 
underestimate now! But the man made noise can be more problematic there, 
you know. So it is good for people who like to take a walk in the forest 
and like to install a hidden wire there to mount their portable RX to it 
and come back a few hours later to bring it home and post process what 
they got :-)

73, Stefan