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Stefan
I am QRV 137 Kcs band. Vy weak PA3 --- stn testing
on 8.97 Kcs approx. Using my 137 antenna temp resonated for 9 Kcs. He seems to
be using qrs 120
and longer dashes, fading out at times possibly
adjusting power.
mal/g3kev
----- Original Message -----
Sent: Friday, August 06, 2010 2:58
PM
Subject: LF: New LF grabber available,
since TODAY :-)
Dear LF,
Yesterday you gave me some ideas about which
filter can be used befor the final stage of my active antenna for 137 kHz.
Maybe there has much to be optimised but today i got a first result that i
want to test now.
I choose 2 band pass filters (33mH parallel 3,3nF +
1,5nF, coupled by a 47 pF capacitor). On one of those LC filters i applied
another 100pF to spread the resonance some 10 Hz... This is the result,
measured on the future QTH:
DLF (not
visible here) is as strong as the LF background noise now(!) and DCF39 just
about 30 dB above the LF noise, that should be not a problem for the soundcard
or the amp. The soundcards noise of the netbook in this mode is -110 dB and
the LF noise abt 20 dB above which looks ok but could be 10 dB more since the
noise could become much lower in winther. The filters slopes are sharp enough
but the bandwith is unstatisfying :-( Thus i will choose another filter type
since i want to have the whole band.
Today i got the idea to use 2nd order
low pass filter (L as shunt, C against GND and the gate of the FET) The peak
should be above the LF band and above DCF39, so maybe on 145 kHz. Additionally
i will use a sharp filter to reject DCF39. This should give a flat level in
the passband and will cancel out the high levels (DLF,DCF39) as necessary as
possible.
Anyway, i want to try the active antenna and its location as
soon as possible, which means TODAY ;-) Thus i have set up the webpage
and run the grabber first on the PC of the VLF grabber with the internal
soundcard, sampling at 44100 samples/s. The window is already running and the
antenna will be connected in some minutes...
So this is the first day
of my LF grabber :-) Much has to be improved but i am looking forward to some
nice DX in the winther :-) So, i invite YOU to produce a signal trace there,
knowing that 137 kHz isn't very exciting any more for some people... It could
be possible that it performs rather bad in the first days since the power
supply, soundcard, noise blanking, accuracy isn't optimal but each recorded
bug will be cancelled step by step.
This is the link: http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_LF_Grabber.html
Best
73, Stefan/DK7FC
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