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Date: Fri, 06 Apr 2018 14:03:05 +0200
From: DK7FC <selberdenken@posteo.de>
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Subject: VLF: Carrier detection  DL > VK7 on 17.4701 kHz
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Hi VLF,

A few weeks ago i had the crazy idea to try an attempt to be detected on 
17.4701 kHz in Tasmania / VK7.

Edgar J.T. is the one on the other side. A few years ago he managed to 
detect my DFCW-180 signal on 136 kHz at two different locations. He is 
currently watching ZEVS as well as other special signals on the VLF.

Using an omidirectional whip antenna on his side we attempted to detect 
a pure carrier transmission that was transmitted daily from my site in 
JN49IK00WD, beginning at March, 15th.
Each day i transmitted from 16...23 UTC with about 1 A antenna current 
on my INV-L antenna wire 30m above the ground. My average ERP estimate 
is 2.5 mW on that  frequency (average estimate, not average ERP ;-) ).

At the beginning there were frequency stability problems on the RX site 
but since the 21st of March the system was running well and stable. So 
we could observe a growing SNR during certain times within the stacked 
files.

We ended up stacking 13 daily transmissions into one file to analyse. I 
build a simple script in vlfrx tools to produce a set of data which was 
plotted in Excel. Here is the latest plot: 
http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF/DL_VK7_17470.png

The curves show the SNR of the carrier for different start times and 
durations. The best SNR (12.70 dB in my stack) is obtained when starting 
at 19:20 UTC and watching the signal in 93 uHz, i.e. 3 hours.

After reaching about 12 dB SNR it became clear that this will become a 
successful detection. So i informed Paul Nicholson to evaluate the files 
and asked for a critical comment regarding the significance. He used his 
new fast PC to run a number of permutations of the files to produce an 
even better SNR, by dropping a few days which do not contribute 
positively to the stack. In the end we ended up at > 14 dB SNR and found 
the strongest peak of the file(s) exactly on the expected frequency.

I leave it to Paul to present the best spectrum peak and comment further 
on the statistical significance of the signal.

BTW this is the path: http://k7fry.com/grid/?qth=QE37PD&from=JN49IK00WD

My thanks and congratulations go to Edgar J.T. for the successful 
carrier detection and the permanent available RX system, as well as for 
daily providing of the txt files containing the FFT data. Oh and not to 
forget about the patience :-)
Also thanks to Markus and Paul for the discussion and support in the 
background. And not to forget about DL4YHF for developing SpecLab, which 
is a part of most of these achievements.

The boundary of the garden fence has been pushed a little bit more these 
days!

73, Stefan