Message-ID: <4D77A221.7050402@iup.uni-heidelberg.de>
Date: Wed, 09 Mar 2011 16:52:01 +0100
From: =?windows-1252?Q?Stefan_Sch=E4fer?=
 <Stefan.Schaefer@iup.uni-heidelberg.de>
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References: <33d07ccc43ec486d83d0d460928f26ad@kabelmail.de>
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Subject: Re: LF: VLF dj8wx on 8970.022Hz
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Hi Uwe,
>
> the test lead of the oscilloscope in use has a resistor of 10Mohm. The 
> oscilloscope advise text says that I have to multiply the result by 10.
>
> OK. I added two other 10Mohm  in series multiplyed the result by 1000 
> and got 40000Vpp
>
> using the twentieth of max TX power. 40kV? Is that possible?
>
If you switch 2 more 10 MOhm resistors in series you have to mulitply 
your result by 3x10. So you should have 1200 Vpp or 426 V rms.
If your maximum antenna current is 3 A (really???!!), you should get 8.8 
kV rms which appears pretty low.
Your L would be less than 50 mH and your C about 6.3 nF. This sounds 
very extreme.
>
> the current from the coile foot into the radials was 0.145A (3 A with 
> max power).
>
How do you measure the antenna current? Can you repeat the voltage 
measuring when using the 1:10 probe without the 20 MOhm in series? The 
probe should withstand 600 Vp normally. You may start with a even lower 
antenna current
>
> who will try to calculate the ERP?
>
It's difficult to do that without knowing the situation about trees and 
buildings near the antenna, especially on VLF but some are able to 
estimate your ERP by the distance and field strength i assume :-)


Looking forward to your transmission! :-)

73, Stefan/DK7FC


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Hi Uwe,
<blockquote cite=3D"mid:33d07ccc43ec486d83d0d460928f26ad@kabelmail.de"  ty=
pe=3D"cite"><span style=3D"font-family: Arial; font-size: 13px;">
  <p><span>the test lead of the oscilloscope in use has a resistor of
10Mohm. The oscilloscope advise text says that I have to multiply the
result by 10.</span></p>
  <p><span>OK. I added two other 10Mohm=A0 in series multiplyed the
result by 1000 and got 40000Vpp</span></p>
  <p><span>using the twentieth of max TX power. 40kV? Is that possible?</s=
pan></p>
  </span></blockquote>
If you switch 2 more 10 MOhm resistors in series you have to mulitply
your result by 3x10. So you should have 1200 Vpp or 426 V rms.<br>
If your maximum antenna current is 3 A (really???!!), you should get
8.8 kV rms which appears pretty low.<br>
Your L would be less than 50 mH and your C about 6.3 nF. This sounds
very extreme.<br>
<blockquote cite=3D"mid:33d07ccc43ec486d83d0d460928f26ad@kabelmail.de"  ty=
pe=3D"cite"><span style=3D"font-family: Arial; font-size: 13px;">
  <p><span>the current from the coile foot into the radials was 0.145A
(3 A with max power). </span></p>
  </span></blockquote>
How do you measure the antenna current? Can you repeat the voltage
measuring when using the 1:10 probe without the 20 MOhm in series? The
probe should withstand 600 Vp normally. You may start with a even lower
antenna current<br>
<blockquote cite=3D"mid:33d07ccc43ec486d83d0d460928f26ad@kabelmail.de"  ty=
pe=3D"cite"><span style=3D"font-family: Arial; font-size: 13px;"><br>
  <p><span>who will try to calculate the ERP?</span></p>
  </span></blockquote>
It's difficult to do that without knowing the situation about trees and
buildings near the antenna, especially on VLF but some are able to
estimate your ERP by the distance and field strength i assume :-)<br>
<br>
<br>
Looking forward to your transmission! :-)<br>
<br>
73, Stefan/DK7FC<br>
<br>
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</html>

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