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Re: LF: VLF surprise

To: [email protected]
Subject: Re: LF: VLF surprise
From: Stefan Schäfer <[email protected]>
Date: Sun, 11 Mar 2012 14:05:42 +0100
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Hi Markus,

Unfortunately the SL instances stopped as i started a remote connection from Darmstadt. Maybe this has to do with the windows remote connection. Also it was not possible to restart the instances then. So i tried Teamviewer and VNC as an alternative remote control tool but somehow it doesn't work. Maybe it has to do with the University-Server, no idea. Never mind. I will be back in Heidelberg on Monday evening and will restart the instances on another PC...

Am 11.03.2012 13:29, schrieb Markus Vester:
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.
Yes these effects are very interesting indeed. Unfortunately we haven't seen how the colours are changing when the terminator crosses the path for a specific transmitter. So i/we have to wait 2 days to see that.
Oh yes, of course. All this is not new and someone else has done it before. It's important to say that each time one is announcing something personally new ;-)

 
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.
Yes, a pity. It was just a spontaneous test, yesterday, but now i like these way of displaying the band and want to establish it in my system. Don't want to miss it after some few hours :-)
One needs a stereo RX for that configuration but on VLF this is no problem since the soundcard...
The screen of the loop is still floating. All ground that i tested have made things worse. I will also try audio decoupling transformers and other stuff in the next days but anyway i think the sensitivity will be quite poor in that location. It would be perfect to have the loop in the forest far away from the city and use a stereo wireless headphone link... I really have to... you know ;-)

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.
Yes, that's the plan. The E field antenna is available (the "old" grabber antenna) and probably i can move the loop on the top of the building. I will do a pre test to see if its actually worth to move the loop. The problem is the CPU load which is not available for so many SL instances in stereo mode...

I'll see ;-)

73, Stefan/DK7FC


 
 
 
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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