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