Re: ELF: ZEVS reception from a small loop

[Markus Vester <markusvester@aol.com>]

Those ZEVS messages seem to consist of simple three-digit numbers. With 0.2 Hz spacing, the frequency ranges 81 to 81.8 and 82.2 to 83 Hz provide ten possible MFSK symbols. Each message is sent twice, separated by a single 80.8 Hz dash. Consecutive messages are always separated by the 82 Hz idle tone.

Assuming that symbol frequencies are counted upwards from 0 to 4 and 5 to 9, Stefan's screenshot would translate to

..7 486 128   731    941        473   018
 
73, Markus  


-----Ursprüngliche Mitteilung-----
Von: DK7FC <selberdenken@posteo.de>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Cc: Renato Romero <contact@vlf.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.
See: http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF/ZEVS__from_JN29PD06BO.png

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: http://www.vlf.it/feletti2/idealloop.html


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 ( http://no.nonsense.ee/qth/map.html?qth=JN29PD06BO&from=jn49ik00wd ). 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: http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF/wide4470.png (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