MIME-Version: 1.0
From: "Hans-Joachim Brandt" <hajo.brandt.dj1zb@t-online.de>
References: <54281B0D.4040202@gmail.com>
In-Reply-To: <54281B0D.4040202@gmail.com>
To: <rsgb_lf_group@blacksheep.org>
Date: 28 Sep 2014 15:13 GMT
Message-ID: <1XYGAg-0aou1o0@fwd30.t-online.de>
Subject: Re: LF: ZEVS RX ant question
Content-Type: Multipart/Alternative;
 Boundary="__Next_1411917180_Part17__"
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Status: O

--__Next_1411917180_Part17__
Content-Type: Text/Plain;
 Charset="WINDOWS-1252"
Content-Transfer-Encoding: 8Bit

Dear Stefan,

I guess You should add a high-pass RC-filter behind your present
low-pass filter (so that the antenna itself is still dc grounded) to
suppress the lower frequencies you do not want. This high-pass filter
may use the two resistors you need for biasing the FET anyway. 

HW?

73 Ha-Jo, DJ1ZB

  

"DK7FC" <73dk7fc@googlemail.com> schrieb: 
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

  
--__Next_1411917180_Part17__
Content-Type: Text/HTML;
 Charset="WINDOWS-1252"
Content-Transfer-Encoding: 8Bit

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD><TITLE>E-Mail Software 6.0</TITLE>
<META content="text/html; charset=ISO-8859-1" http-equiv=Content-Type>
<META name=GENERATOR content="MSHTML 8.00.6001.23588"></HEAD>
<BODY aLink=#000080 leftMargin=0 link=#000000 topMargin=0
bgColor=#ffffff 
vLink=#000000 marginheight="0" marginwidth="0"><FONT color=#000000
size=3 
face=Arial>Dear Stefan,<BR><BR><EM>I&nbsp;guess You should add a
high-pass 
RC-filter behind your present low-pass filter&nbsp;(so that the antenna
itself 
is still&nbsp;dc grounded)&nbsp;</EM>to suppress the
lower&nbsp;frequencies you 
do not want. This high-pass filter may use the two resistors you need
for 
biasing the FET anyway.&nbsp;<BR><BR>HW?<BR><BR>73 Ha-Jo, 
DJ1ZB<BR><BR>&nbsp;</FONT>&nbsp;<BR><BR>"DK7FC"
&lt;73dk7fc@googlemail.com&gt; 
schrieb: 
<BLOCKQUOTE 
style="BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; PADDING-RIGHT:
0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px">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>&nbsp;Advice is 
  apprechiated. Where are the experts?<BR><BR>73, 
Stefan/DK7FC<BR></BLOCKQUOTE><FONT color=#000000 size=3
face=Arial>&nbsp;</FONT> 
</BODY></HTML>

--__Next_1411917180_Part17__--