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Hi Stefan, LF,
thanks for sharing this, fascinating indeed!
The uploads to the web apparently froze somtime
during the night. Good thing about this is that the "slow MSK" pic
still shows some spectacular colour fading effects on DHO.
Regarding SNR, I also found it hard to get low
noise from any loops located near buildings,
as magnetic fields from cables and appliances are not
well contained inside. Perhaps the best solution would be combined RDF,
mode using E-field for brightness (and SNR), and the loops only as an
auxiliary colour channel. This also resolves the 180°
ambiguity. You will need to make an audio 90°
phase-difference network to combine the two loops, eg. by scaling one of
the well-known opamp designs to our frequency range. A common
difficulty is the tight phase tolerance for SSB generation, but
it will be much less stringent for an RDF
application.
Best 73,
Markus (DF6NM)
Sent: Saturday, March 10, 2012 11:34 PM
Subject: LF: VLF surprise
VLF,
I just build an arrangement of 2 orthogonal
delta loops with a
circumference of 10m. They are not resonated and there is
still no
preamp in use, so they are directly connected to the
soundcard.
They are made out of CAT5 STP cable, so it is a shielded loop with
8 turns.
Now it is possible to run SpecLab in the Colour Direction Finder
mode.
Tonite i will be silent on LF just to see how the wideband windows
look
on VLF. That is a new dimension for me, like switching from black-white
TV to colour TV ;-)
Sensitivity is about 15 dB down to the E field
grabber on the building.
This loop is 7m above ground but on the ground of
the 2nd floor of that
building. Room for improvements. Anyway it is most
interesting to see
the different colours of DHO38.
See http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html
73,
Stefan/DK7FC
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