Message-ID: <4DA89BBA.1010106@iup.uni-heidelberg.de>
Date: Fri, 15 Apr 2011 21:25:46 +0200
From: =?ISO-8859-15?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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To: rsgb_lf_group@blacksheep.org
Subject: LF: VLF grabber at DK7FC
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Dear group,

Today, my VLF grabber at 
http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber.html 
becomes 1 year old :-)

I've never thought that it will be so sensible and will see so many 
stations, even with usual LF home antennas and moderate power. The 
circuit of the active antenna was modified several times. Also Spectrum 
Lab by DL4YHF plays a dominant role here. By improving the noise 
reduction settings, we won another 2 dB (about).

First it was a idea of Paul Nicholson to choose a compromise of a long 
(enough) "carrier" and sending informations. So i came to the good old 
"DFCW-600". Since my signal was strong out of 40km distance i wanted to 
add a DFCW-60 and DFCW-3 window, to monitor my own signal in faster 
modes. For test purposes i arranged a DFCW-6000 window. The idea was 
that someone who prepares to be visible in 600 could see his signal in 
6000 and then knowns how many dBs are still missed. OE5ODL for example 
showed often that he is visible in 6000 but just sometimes, with the 
balloon, in 600.
Now we arrived at even 60000 (= 47 uHz). Stations like DJ8WX became 
regularly visible. But there seems to be a limit, given by the VFO 
accuracy, time and phase instabilities at higher distances.
The Alpha stations are a perfect reference and since having a stable RX 
is essential and there were often questions about the availability of 
RSDN-20, i added the Alpha window, not only to check if my GPS module is 
still locked.
The wideband window gives a good overview of the current QRN situation, 
solar activities and the presence or absence of military MSK stations or 
fauls of the rig, that shows in a sudden loss of sensitivity.

Thank you for the interest of 7314 visitors out of 60 countries (34 of 
51 US states) and 198665 pageviews so far :-) I'll keep the service 
running as long as possible, and this may be a looong time!
Stations who appeared there so far were: DF6NM, OE5ODL, OE3GHB, DJ8WX, 
OK2BVG, DK7FC and a small sign of PA3CPM
I hope to see more stations soon!


73, Stefan/DK7FC