Re: ULF: 7.9 km distance on the 101 km band

[DK7FC <selberdenken@posteo.de>]

PS: Another spectrogram: It is even visible in 3.8 mHz: 
https://dl.dropboxusercontent.com/u/19882028/ULF/ULF_7.9km_3.8mHz.png
Am 11.07.2016 23:36, schrieb DK7FC:
> 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