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From: Markus Vester <markusvester@aol.com>
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Date: Wed, 10 Jul 2013 13:04:55 -0400 (EDT)
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 Content preview:  Pieter-Tjerk's sketch of equipotentials around a mast is a
    good explanation of the effective height of a capacitive probe on a mast.
    Dioes anyone knowĀ a simple analytic formula for that E-field enhancement
    near the apex, maybe modelling the mastĀ withĀ a tall and slim ellipsoid?
    Ā Regarding ground on space ships: I have always wondered how the TACAMOĀ
    guys excite the VLF transmit long wire dangling from their aircraft. Does
    theĀ aitframe itself provide enough capacitance against free space? Or do
    they haveĀ a second (perhaps shorter)Ā wire being dragged at a higher angle?
    Ā Best 73, Markus (DF6NM) [...] 
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Subject: Re: LF: VK1OD's analysis of the MiniWhip antenna - mast, aircraft
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Pieter-Tjerk's sketch of equipotentials around a mast is a good explanation=
 of the effective height of a capacitive probe on a mast. Dioes anyone know=
=C2=A0a simple analytic formula for that E-field enhancement near the apex,=
 maybe modelling the mast=C2=A0with=C2=A0a tall and slim ellipsoid?
=C2=A0
Regarding ground on space ships: I have always wondered how the TACAMO=C2=
=A0guys excite the VLF transmit long wire dangling from their aircraft. Doe=
s the=C2=A0aitframe itself provide enough capacitance against free space? O=
r do they have=C2=A0a second (perhaps shorter)=C2=A0wire being dragged at a=
 higher angle?
=C2=A0
Best 73,
Markus (DF6NM)


-----Urspr=C3=BCngliche Mitteilung-----=20
Von: Pieter-Tjerk de Boer &lt;ptdeboer@cs.utwente.nl&gt;
An: rsgb_lf_group &lt;rsgb_lf_group@blacksheep.org&gt;
Verschickt: So, 7 Jul 2013 12:17 pm
Betreff: Re: LF: VK1OD's analysis of the MiniWhip antenna

=20
On Sat, Jul 06, 2013 at 06:05:01PM +0200, Stefan Sch=C3=A4fer wrote:=20
=20
&gt; Am 06.07.2013 15:16, schrieb Pieter-Tjerk de Boer:=20
&gt; &gt;This view also at least approximately matches VK1OD's NEC4 calcula=
tion,=20
&gt; &gt;in the sense that he finds an output voltage which is of the order=
 of=20
&gt; &gt;the field strength times the antenna height.=20
&gt; Not the antenna height but the distance between the probe and the=20
&gt; grounded shield of the coax, or the grounded part of the circuit,=20
&gt; which is the closest grounded part to the probe.=20
=20
Actually, I meant the real height above ground, multiplied by the=20
free-space field strength.=20
=20
But of course, you are right that what the device responds to, is the=20
field between the probe and the nearby ground. However, the field=20
strength there will be much larger, due to the fact that the ground=20
has been "brought up".=20
This much larger field strength mostly compensates for the much smaller=20
distance, so the output voltage is still roughly the same as when=20
one just multiplies the real height above ground by the free-space field=20
strength.=20
=20
See the attached sketch: the equi-potential lines in the area near the=20
probe are much closer together because the pole is at ground potential.=20
=20
B.t.w., a member of this mailinglist contacted me off-list and pointed=20
out that there is an article in VHF Communications 96/2 in which this is=20
discussed in more detail. A German version of the same article has=20
appeared in UKW-Berichte in 1994/1995 (but those years unfortunately are=20
missing in our radio club's collection).=20
=20
&gt; The potential=20
&gt; difference, the intagral E . ds... Of course the E field is not=20
&gt; homogen in the electrode arrangement, not a simple idealized plate=20
&gt; capacitor...=20
=20
Indeed.=20
=20
73, Pieter-Tjerk, PA3FWM=20
=20


----------MB_8D04BA6BC1BAF94_B58_237BC1_webmail-d261.sysops.aol.com
Content-Transfer-Encoding: quoted-printable
Content-Type: text/html; charset="utf-8"


<div style=3D"FONT-FAMILY: arial; COLOR: black; FONT-SIZE: 10pt">Pieter-Tje=
rk's sketch of equipotentials around a mast is a good explanation of the ef=
fective height of a capacitive probe on a mast. Dioes anyone know&nbsp;a si=
mple analytic formula for that E-field enhancement near the apex, maybe mod=
elling the mast&nbsp;with&nbsp;a tall and slim ellipsoid?<SPAN style=3D"DIS=
PLAY: inline-block" contentEditable=3Dfalse></SPAN></div>


<div style=3D"FONT-FAMILY: arial; COLOR: black; FONT-SIZE: 10pt">&nbsp;</di=
v>


<div style=3D"FONT-FAMILY: arial; COLOR: black; FONT-SIZE: 10pt">Regarding =
ground on space ships: I have always wondered how the TACAMO&nbsp;guys exci=
te the VLF transmit long wire dangling from their aircraft. Does the&nbsp;a=
itframe itself provide enough capacitance against free space? Or do they ha=
ve&nbsp;a second (perhaps shorter)&nbsp;wire being dragged at a higher angl=
e?</div>


<div>&nbsp;</div>


<div>Best 73,</div>


<div>Markus (DF6NM)<br>
</div>


<div><br>
</div>
-----Urspr=C3=BCngliche Mitteilung----- <br>
Von: Pieter-Tjerk de Boer &lt;ptdeboer@cs.utwente.nl&gt;<br>
An: rsgb_lf_group &lt;rsgb_lf_group@blacksheep.org&gt;<br>
Verschickt: So, 7 Jul 2013 12:17 pm<br>
Betreff: Re: LF: VK1OD's analysis of the MiniWhip antenna<br>
<br>


<div style=3D"BACKGROUND-COLOR: #fff; MARGIN: 0px; FONT-FAMILY: Tahoma, Ver=
dana, Arial, Sans-Serif; COLOR: #000; FONT-SIZE: 12px" id=3DAOLMsgPart_0_a3=
3a74ba-9d4b-40ef-997f-20c7835c40c0><PRE style=3D"FONT-SIZE: 9pt"><TT> <br>
On Sat, Jul 06, 2013 at 06:05:01PM +0200, Stefan Sch=C3=A4fer wrote: <br>
 <br>
&gt; Am 06.07.2013 15:16, schrieb Pieter-Tjerk de Boer: <br>
&gt; &gt;This view also at least approximately matches VK1OD's NEC4 calcula=
tion, <br>
&gt; &gt;in the sense that he finds an output voltage which is of the order=
 of <br>
&gt; &gt;the field strength times the antenna height. <br>
&gt; Not the antenna height but the distance between the probe and the <br>
&gt; grounded shield of the coax, or the grounded part of the circuit, <br>
&gt; which is the closest grounded part to the probe. <br>
 <br>
Actually, I meant the real height above ground, multiplied by the <br>
free-space field strength. <br>
 <br>
But of course, you are right that what the device responds to, is the <br>
field between the probe and the nearby ground. However, the field <br>
strength there will be much larger, due to the fact that the ground <br>
has been "brought up". <br>
This much larger field strength mostly compensates for the much smaller <br=
>
distance, so the output voltage is still roughly the same as when <br>
one just multiplies the real height above ground by the free-space field <b=
r>
strength. <br>
 <br>
See the attached sketch: the equi-potential lines in the area near the <br>
probe are much closer together because the pole is at ground potential. <br=
>
 <br>
B.t.w., a member of this mailinglist contacted me off-list and pointed <br>
out that there is an article in VHF Communications 96/2 in which this is <b=
r>
discussed in more detail. A German version of the same article has <br>
appeared in UKW-Berichte in 1994/1995 (but those years unfortunately are <b=
r>
missing in our radio club's collection). <br>
 <br>
&gt; The potential <br>
&gt; difference, the intagral E . ds... Of course the E field is not <br>
&gt; homogen in the electrode arrangement, not a simple idealized plate <br=
>
&gt; capacitor... <br>
 <br>
Indeed. <br>
 <br>
73, Pieter-Tjerk, PA3FWM <br>
 <br>
</TT></PRE><br>
</div>
<br>

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