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

[Markus Vester <markusvester@aol.com>]

Hi Stefan,

the spectrograms from your far-field recording are now showing a very clear trace on 2970.0025 Hz. Congratulations!

I wonder why the postprocessing analysis takes so long. Apparently SpecLab needs to replay the recordings at the original speed to be able to use DSP features like 1pps lock and noise blanking?

All the best,
Markus (DF6NM) 

-----Ursprüngliche Mitteilung-----
Von: DK7FC <selberdenken@posteo.de>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Mi, 3 Aug 2016 3:14 pm
Betreff: Re: ULF: 17 km experiment on the 101 km band 2/3

Hi all,

It took some time to prepare the post-processing of the data. I'm now playing the wav files in windows media player (!! :-) ) and feed the output to VAC3 which is then read by 3 SpecLab instances. The incoming spectrograms are shown on the bottom of this page: http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html  The spectrograms become updated each 10 minutes (100 minutes for the 47 uHz instance).
The end is to be expected in 2 days.
I already saw the trace in 212 uHz, as well as the frequency shift (had to restart the analysis for various reasons). But i didn't see the end of the recording yet. In the end of the files, which represent the data of monday morning, the traces should have their best SNR. Also the frequency shift down from 2970.0025 Hz to 2970.0000 Hz should become well visible.
But so far i can say that the SNR is less than expected. This is most likely due to the high QRN and secondly due to the non ideal matching of the antenna resonance (to sharp and not centered on 2970).

73, Stefan

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.