Hi Henny, VLF,
I run various reprocessings from the yesterdays 4 hour recording (abt
10...14 UTC). To get an overview, this is the wideband spectrogram
http://dl.dropbox.com/u/19882028/VLF/wide.jpg
Looks good i find. The difference of the lower cutoff frequency when
changing the RC highpass is here:
http://dl.dropbox.com/u/19882028/VLF/Comp.jpg Very odd, the levels in
the higher VLF are changing too, a slight decrease, although the
resistance is higher. Has someone ann explanation for that effect?
A spectrogram of the ULF range
http://dl.dropbox.com/u/19882028/VLF/ULF.jpg and ELF
http://dl.dropbox.com/u/19882028/VLF/ELF.jpg
For comparison, the spectrogram of my grabber in the city, covering the
same time http://dl.dropbox.com/u/19882028/VLF/widebandcity.jpg The
sferics appear stronger, i.e. have a higher S/N while they seem to be
lost in the noise on the /p location and antenna. The antenna is the
same design (except the 1 MOhm resistor) as in the city and the MSKs
appear at good strength too.
Has someone an explanation? May this resistor generate noise or where
is the high noise floor coming from? I also thought about microphonic
effects...
Unfortunately there was no detection of PA3CPM in "600" and in "6000",
http://dl.dropbox.com/u/19882028/VLF/600.jpg
http://dl.dropbox.com/u/19882028/VLF/6000.jpg Maybe due to the same
reacon.
Why does the same design produce good results in the city but not in
the forest? Where is the noise coming from? Why does G3ZJO clearly
receive ZEVS at 82 Hz with this design but not i ?
I'll go on testing, investigating and playing :-)
73, Stefan/DK7FC
Am 02.04.2012 20:22, schrieb Stefan Schäfer:
Hi Henny, VLF
Thanks for your transmission.
It was a nice day and i took a 4 hour recording during climbing on
trees, sleeping and eating in a hammok :-)
Right now i'm running various reprocessings and hope to find your
signal out of the noise. I will post screenshots of the complete
session later.
If someone wants to play with the recording wav file, it is available
at
http://dl.dropbox.com/u/19882028/LF/audio/EfieldSteinbruchOhne5k6ExtAkku.WAV
for a while. It is a 1.95 GB file sampled at 72 k/s.
I switched a 1 MOhm resistor in series to the 5k6 resistor of my active
receive antenna. The 5k6 resistor should form a high pass with the 10
nF capacitor in the circuit
(http://www.iup.uni-heidelberg.de/schaefer_vlf/8,97kHz%20active%20E%20field%20antenna%20by%20DK7FC.jpg)
By
adding the 1 MOhm resistor in series it was clearly seen that the
lower cut off frequency dropped to < 1 kHz. The highpass was
intended to reduce mains hum and all the stuff below 4 kHz but there in
the forest, this is no problem :-)
73, Stefan/DK7FC
PS: On my VLF grabber in the city i see a trace at 8970.002 Hz, maybe
this was DF6NM transmitting a test signal too?
Am 02.04.2012 10:11, schrieb henny van elst:
Gm Stefan,lf
the tx is on,8.970 Khz
henny cpm
73's
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