From: DK7FC <73dk7fc@googlemail.com>
Message-ID: <54281B0D.4040202@gmail.com>
Date: Sun, 28 Sep 2014 16:28:29 +0200
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To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Subject: LF: ZEVS RX ant question
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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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HI VLF, <br>
<br>
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:
<a class="moz-txt-link-freetext" href="https://dl.dropboxusercontent.com/u/19882028/VLF/ZEVS%20test%20ant.jpg">https://dl.dropboxusercontent.com/u/19882028/VLF/ZEVS%20test%20ant.jpg</a><br>
<br>
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:
<a class="moz-txt-link-freetext" href="https://dl.dropboxusercontent.com/u/19882028/VLF/Garden%20T%20antenna%20VLF%201.png">https://dl.dropboxusercontent.com/u/19882028/VLF/Garden%20T%20antenna%20VLF%201.png</a><br>
<br>
I remember from tests with a small active antenna for VLF, where i used
100 MOhm resistors on the gate, that <b>charged humidity </b>caused
much noise. <br>
Could this be the same effect here? <br>
Should i try to use a lower input impedance of the preamp? <br>
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? :-)<br>
<br>
 Advice is apprechiated. Where are the experts?<br>
<br>
73, Stefan/DK7FC<br>
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