HI VLF,
Yesterday i tried again to receive ZEVS. I didn't know if it was on air
but gave it a try. Recorded about 2 hours of the VLF spectrum received
on my T antenna (i.e. E-field). I also used a source follower (J310)
but added a 3 stage RC filter in front of the gate. I thought i can
afford some pF against ground now with the relatively large antenna
which must have about 150 pF. I used this circuit:
https://dl.dropboxusercontent.com/u/19882028/VLF/ZEVS%20test%20ant.jpg
But somehow the spectrum looks not as expected. While the MSKs are
still strong, there is much noise below 2 kHz and the sferics appear to
be quite weak. See:
https://dl.dropboxusercontent.com/u/19882028/VLF/Garden%20T%20antenna%20VLF%201.png
I remember from tests with a small active antenna for VLF, where i used
100 MOhm resistors on the gate, that charged humidity caused
much noise.
Could this be the same effect here?
Should i try to use a lower input impedance of the preamp?
Maybe you remember, there were certain transistors, several decades
ago, they were called bipolar transistors, NPN and PNP. Maybe i should
try one of them? :-)
Advice is apprechiated. Where are the experts?
73, Stefan/DK7FC
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