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Re: ULF: 17 km experiment on the 101 km band 3/3, summary

To: [email protected], Renato Romero <[email protected]>
Subject: Re: ULF: 17 km experiment on the 101 km band 3/3, summary
From: DK7FC <[email protected]>
Date: Fri, 05 Aug 2016 15:28:11 +0200
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Hi ULF friends,

This is the summary of my portable RX experiment in 16.8 km distance to my transmit site. It is into the far field of the 101 km RF wave.
A 100 nW ERP signal was sent and recorded for nearly 2 days.
The recording was started on Saturday, 30th of July (14:58 UTC) and was finished on Monday, 01st of August (12:25 UTC). The transmission was a carrier sent on 2970.000 Hz, it was shifted by +2.5 mHz at 8 UTC on Sunday and again shifted by -5 mHz on Monday, 8 UTC.
In the post processing of nearly 30 GB wav files the signal was successfully detected.
Due to the exceptionally high QRN levels (even for the summer time), the SNR was lower than expected, however the traces and frequency shifts are clearly visible.
Spectrogram of the signal in 212 uHz FFT bin width: https://dl.dropboxusercontent.com/u/19882028/ULF/17km212.jpg
Spectrogram of the signal in 47 uHz FFT bin width: https://dl.dropboxusercontent.com/u/19882028/ULF/17km47.jpg
A wideband spectrogram giving an idea about the natural and man made noise conditions as well as the frequency response of the tuned loop antenna: https://dl.dropboxusercontent.com/u/19882028/ULF/17kmwide.jpg
Wideband spectrogram zoomed to the spectrum of interest: https://dl.dropboxusercontent.com/u/19882028/ULF/17kmwide3.jpg

The best SNR shown is 12 dB in 212 uHz and 17 dB in 47 uHz.
During the post-processing procedure it happened that SpecLab has plotted a few pixel twice. I don't know the reason.

It looks like i am now seeing the natural background noise on 2970 Hz even in quiet periods (the faint vertical traces). However the man made noise is still playing a role in this QTH.

Further informations can be found in the older emails below.

73, Stefan

PS: A next experiment is planned in a few weeks. The goal is 30 km distance. With lower QRN levels, a better tuned antenna and higher power (already running!) this should give even better results.


Am 01.08.2016 19:38, schrieb DK7FC:
Hi all,

The second part (2/3) of my 17 km experiment is successfully completed.

Today i've been on the quiet location in 17 km distance again. In fact it is 16.8 km. For savety reasons i didn't want to tell the exact location  but now i can say that it was in http://no.nonsense.ee/qth/map.html?qth=JN49KM06AM
You will see there is not much that can generate QRM :-)
This is the path between transmitter and receiver: http://no.nonsense.ee/qth/map.html?qth=JN49KM06AM&from=jn49ik00wd

If the signal is detectable, it would probably be the first far field detection of a signal generated by radio amateurs on the 101 km band. Or even the first ULF far field signal? I don't know...

Everything was possible during that time, a lot of things that could have gone bad or good. Everything went well!
When coming to the location at saw that:
-The equipment was still there (nothing stolen)
-The recording was still running (no damage of the arrangement and no crash of the Raspberry Pi2)
-The batteries were at 12.09 V (no deep discharge)
-The arecord process on the Raspi did not crash, 29.2 GB wav file data (splitted in 2 GB files) were recorded to the USB stick.

Everything went well, the equipment is back in the shack, the batteries are now loading again.

The QRN has been extreme this weekend. There are certainly better times in the year for such a test :-) I am optimistic to find the signal anyway because the background noise was very low (between the sferics) in this location.
Due to the high QRN i decided not to transmit EbNaut but simply do a frequency shift as shown in this spectrogram taken on my remote grabber: https://dl.dropboxusercontent.com/u/19882028/ULF/wald7_fshift.jpg
This is the trace to be found in my post-processing that i will start now!
I will show the signal in different bandwidths, if detectable....

Soon more...

73, Stefan


Am 31.07.2016 15:18, schrieb DK7FC:  
[...]
Thanks. But so far there is no result. On monday i will drive there again and hope to find the equipment and a few 10 GB of wav data :-)
But i'm optimistic. I took a short recording before i started the long recording. It is for finding the equipment again because i didn't exactly where i have been in the forest :-) The recording contains the NMEA data and so the exact location :-)
On this recording i saw that the noise background is MUCH lower than on the tree and in pre-tests in 5 km distance to the city.
Here is a spectrum of the recording with 250 ms scroll rate: https://dl.dropboxusercontent.com/u/19882028/ULF/JN49KM.jpg
You see the resonance is a bit sharp and not perfectly on the frequency but i hope it will work well anyway. It even looks like the gain of the preamp is not sufficient. On the test QTH in 5 km distance to the city the gain was high enough (the noise background increased 15 dB relative to a dummy antenna). So this gives an idea how low the background noise is in this location!
When this test is completed i will do another one in 30 km distance with 6 dB more pwoer :-) [...]
Ah BTW here is a photo of the loop in the forest: https://dl.dropboxusercontent.com/u/19882028/ULF/20160730_170105.jpg
Not so easy to find between the trees but it is visible. The circumference is 40m and the height above ground is maybe 4m.
And https://dl.dropboxusercontent.com/u/19882028/ULF/20160730_165911.jpg shows the recording equipment which will hopefully not be stolen...


Am 31.07.2016 00:28, schrieb DK7FC:
[...] My 17 km distance experiment is running now! I have installed the loop antenna somewhere in JN49KM. The Raspy is now recording stereo wav files to the 32 GB USB stick... I'm using 2x 7 Ah lead acid gel batteries for the supply. 1PPS+NMEA is used on the right channel.
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