Hi Luis,
Am 07.06.2019 08:34, schrieb VIGILANT Luis Fernández:
I have the overnight spectrogram at 1min per pixel. The gap on
the left at about 21h is the test
without antenna
The elevators QRM is clearly identified and drops
from about 00utc to 05utc. Best, lower noise from 03 to 05utc
Someone came home late at night! :-)
Anyway amazingly quite, considering this is urban
enviroment and the building tower holds 78 neighbours with all kind
of noisy sources at each home. And a couple of 3
phase 380V variators for the lifts just a few meters under the antenna
Hmmmmm, something is still missing. The QRN usually drops below 4 kHz,
like seen on the upper image of my grabber
http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html
Now in summer at daylight, that difference (e.g. 8 kHz vs. 3 kHz) can
reach > 20 dB, easily.
I still don't see that signal drop on your image, so something is not
running optimal. Let's see what happens when you put the transformer on
the roof. I think the signal levels will rise at least by 10 dB and
hopefully the QRM will not.
73, Stefan
PS: Maybe use a relay to switch the coax cable between LF TX and VLF RX?
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