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Re: ELF: ZEVS reception from a small loop

To: [email protected]
Subject: Re: ELF: ZEVS reception from a small loop
From: DK7FC <[email protected]>
Date: Tue, 26 Sep 2017 00:05:42 +0200
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Hi Markus,

Am 25.09.2017 17:03, schrieb Markus Vester:
Have you also tried to look for Schumann resonances in the recording?
I tried but saw nothing. So either the signal level from the loop is to small (i think so) and/or the frequency response of the preamp also contributes.

Instead of the 84 turns, you could probably employ a single turn loop with a transformer. So perhaps your antenna in the tree might receive ELF as well?
You know, on the tree i'm using a single turn loop and a ferrite transformer with 100 turns secondary. But the preamp was designed for a low power consumption. The LT1028 must run from the 12 V level, 5 V is not enough. VLF was a rather low priority during the time i built the preamp.

BUT: You may have noticed some interruptions on the grabber yesterday. This happend because i set up a new firmware on the Raspi (now Linux 8 / Jessie). vlfrx tools is also installed already. I want to observe if the new system is running stable, then i consider to install one of the octo soundcards there. And then i could run 2 channels for MF and 3 channels for VLF and 1 channel for PPS. If i do so, i would need a new preamp anyway. And then i can watch the E field from there too. But that will take time...

73, Stefan

Best 73,

-----Ursprüngliche Mitteilung-----
Von: DK7FC <[email protected]>
An: rsgb_lf_group <[email protected]>
Cc: Renato Romero <[email protected]it>
Verschickt: Mo, 25. Sept 2017 15:18
Betreff: ELF: ZEVS reception from a small loop

Hi LF friends,

You know, a few weeka ago i've been in France. We had a field day and i tested my small loop with its new preamp. Description below.
>From a handy loop with just 0.8 m diameter and 84 turns i didn't expect much. However i saw my 4470.005 Hz carrier quite well even in 424 uHz FFT bandwidth which is not bad at all for 250 km distance. It even was a noisy day.

But now: I reprocessed the recording (which was done by the Raspi and vlfrx tools) again, looking for ZEVS on 82 Hz.
To my surprise ZEVS has a very good SNR from that small antenna! It was up to 25 dB in 3.8 mHz! That's the celarest signal i saw from ZEVS, so far. For the spectrogram i used a 1.5 kHz low pass filter and a noise blanker.

So my loop setup seems to be promising for the next 970 Hz experiment as well :-)

73, Stefan

PS: The preamp design is taken from:

Am 18.09.2017 00:56, schrieb DK7FC:

Am 31.08.2017 22:37, schrieb DK7FC:
This weekend i will be in France again, JN29OD96SK , on a field day with the radio club. I plan to receive the 4470 Hz signal with a small loop and its new preamp and the octo soundcard. Thus i want to run a carrier again on 4470.005 Hz. Tomorrow, Friday, i will transmit the EbNaut message again. After that, the carrier will continue until sunday. With some luck i hope you can decode the message when including the friday transmission. If not, i could continue to transmit on monday...

It took some time but now i have some results from that experiment. I actually placed a 84 turn loop with 0.8 m diameter and a low noise preamp between some trees in France, JN29PD06BO.
A path of 250 km or 3.7 wavelengths between RX and TX ( ). Quite a compact RX system for VLF. I did not prepare the experiment as good as possible, there was no E field RX together with the loop. H field only. It was mainly another test of the octo-soundcard and a first test for the samll loop and its LNA.
I converted the data files recorded by vlfrx tools into a wav file and analysed it in SpecLab. Here is a wideband spectrogram showing the QRN: (time markers are incorrect there)

On sunday morning, 3rd Spetember when i looked at the installation i found that the preamp was disconnected from the battery. It must have been an animal walking arround into the field, stumbling over the cable ;-) . Fortunately the interruption took just about one hour ;-)
Assuming that vlfrx tools correctly resampled to 24 kS/s i run the file into SpecLab set to 47 uHz FFT bin width, hoping to see a trace/peak at 4470.005 Hz.
And indeed, there is something! See attachment. That's a first trace from DL to F on the 67 km band :-) About 18 dB in 47 uHz during the best time, much more than i expected.

Another success is that i managed to produce a first spectrum peak and generated a png file using vlfrx tools. The procedure is based on Paul's advice. :-)

73, Stefan

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