Hi VLF/ULF,
Since two days i have an E-field receiver installed on the tree. As
usual, the spectrogram covers a range 0...24 kHz. The lower cut off
frequency of this new antenna seems to be arround 200 Hz, far better
than the loops i have installed at the moment (this will be improved too).
There are some things to improve, like a better filtering of the ripple
on the 5 V supply (the DC/DC converter supplying the Raspi and other
receivers).
A first impression can be seen at
http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html .
The upper window does now show the E field spectrogram. When clicking on
the image, it turns to the EW loop, then to the NS loop and then to the
RDF spectrogram which is still from the two loops only.
Actually i wanted to build an E field RX for VLF much earlier but other
projects were more prirised. But now, since having that large ground
loop antenna, allowing to operate below 1 kHz, i need a sensitive RX up
there. Thus the E field RX quickly rised to the top of the priority
list. And now it is there. So far it looks like the sensitivety at 970
Hz is excellent, at least relative to the loops.
Furthermore i do now have a 3 axis RX and the lossless compressed vtflac
stream is stored at 48 kS/s to a 1 TB HDD, covering about 40 days.
It will be interesting to see how the E field performs relative to the
combined loops, and how a cardioid antenna will increase the SNR even more.
A transmission on 970 Hz will follow in the near future.
73, Stefan
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