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Date: Mon, 11 Jul 2016 23:36:39 +0200
From: DK7FC <selberdenken@posteo.de>
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Subject: ULF: 7.9 km distance on the 101 km band
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Status: O

Hi all,

Today i woke up early in the morning, 05:00 AM, drunk a coffee and drove 
on the hill where i intended to receive my own 100 nW ERP ULF signal in 
a distance of 7.9 km.
This is the path and locations: 
http://no.nonsense.ee/qth/map.html?qth=JN49JL01LT&from=JN49IK00WD
The first time i used the portable stereo recorder with PPS+NMEA on the 
right channel. 130 minutes were recorded. The receive antenna was an 
active E field antenna, modified for ULF reception. The RX location is a 
tower on a hill, 570m ASL. The antenna was mounted in about 35m AGL. The 
tower is quite distant from the city and villages but there is 
electricity, so the QRM / mains hum was terrible!
A first spectrogram shwing the unfiltered signal over the recording time:
https://dl.dropboxusercontent.com/u/19882028/ULF/ULF_Teltschikturm_wide_unfiltered.png
When applying Paul's hum filter (implemented in SpecLab) it looks MUCH 
better:
https://dl.dropboxusercontent.com/u/19882028/ULF/ULF_Teltschikturm_wide_humfil.png
Concentrated arround the interesting range: 
https://dl.dropboxusercontent.com/u/19882028/ULF/ULF_Teltschikturm_1k-5k_humfil.png

Then a band pass filter and NB was applied to generate narrow band 
spectrograms.
Considering the strong mains hum i didn't expect much BUT, i've got a 
very clear peak in 424 uHz:
https://dl.dropboxusercontent.com/u/19882028/ULF/ULF_Teltschikturm_424uHz_NB_humfil.png
The average SNR is about 15 dB, the best peak was at 20 dB SNR, much 
more than i expected.
Now, 7.9 km is the best distance so far on the 101 km band. That's 49% 
of the far field border distance.

The nice SNR makes me optimistic to see the signal in the far field. A 
next step should be a distance of about 17 km. It still looks like i am 
not band noise limited on the RX side, so maybe there can be an 
improvement of a few dB. Also i am planning to try a loop in the next 
test. Preparations will be done in a few minutes :-) The idea is to use 
a 4 turn 40m circumference (slightly) resonated loop...

Certainly it would be better to show a somewhat modulated signal to get 
a better proof that it's actually my signal, however i am still waiting 
for a significant peak on Paul's RX site, so i don't want to interrupt 
the transmission (15 days now). I checked other frequencies like 2971 
and 2969 Hz, didn't find a stable signal, so there is no cross-talk from 
the PPS signal.

73, Stefan