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	<C3D24A10-4CE6-46F8-B312-85311A1433B0@numeo.fr>
Date: Mon, 26 Jul 2010 15:09:53 +0100
Message-ID: <AANLkTim8Wn24AuBvmYO94VxzsGNKwW62PVNcrj2fUyGg@mail.gmail.com>
From: Andy Talbot <andy.g4jnt@googlemail.com>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: David Gibson on Earth antennas and propagation below 9 kHz
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I was thinking about this, and thoughts turned to a rather simpler antenna;
the folded dipole and how it would behave when electrically short.

A simple non-folded  electrically short dipole (negelecting all losses)  has
Rin proportional to 1/L^2 and a highly capacitive reactive term

 A folded half-wave dipole fed conventionally has Rin about 4* that of a
normal dipole due to current sharing in the legs -.

Now the conumdrum - what does an electrically short folded dipole look
like?     It has got to be inductive, since we're feeding into a squashed
shorted turn, and presumably the current distribution looks short
dipole-ish.

So is it a loop, is it a dipole, is it both, how can it be both, if it is
what's its radiation pattern ?
Similar to the ground loop/dipole question ?

And is there a length where the inductance of the loop bit resonates with
the capacitance that 'ought' to be there due to its also being a short
dipole.

?????????????????????????????????????

Andy
www.g4jnt.com
(not really an antenna sort of person)


On 21 July 2010 08:12, John Rabson <john.rabson@numeo.fr> wrote:

>   Reposted by permission
>
>
> John F5VLF
>
>  The antenna is a "horizontal end-grounded line current" antenna; commonly
> referred to as a "horizontal end-grounded electric dipole".  The word
> "dipole" is often used a bit too loosely, although that is a moot point. If
> you think "horizontal electric dipole" you get the general idea: its an
> electric dipole, not a loop antenna.
>
>

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<div>I was thinking about this, and thoughts turned to a rather simpler an=
tenna;=A0 the folded dipole and how it would behave when electrically shor=
t.</div>
<div>=A0</div>
<div>A=A0simple non-folded =A0electrically short dipole (negelecting all=
 losses)=A0 has Rin proportional to 1/L^2 and a highly capacitive reactive=
 term</div>
<div>=A0</div>
<div>
<div>A folded half-wave dipole fed conventionally has Rin about 4* that of=
 a normal dipole due to current sharing in the legs -.</div>
<div>=A0</div></div>
<div>Now the conumdrum - what does an electrically short folded dipole loo=
k like?=A0=A0=A0=A0 It has got to be inductive, since we&#39;re feeding in=
to a squashed shorted turn, and presumably the current distribution=A0look=
s short dipole-ish.</div>

<div>=A0</div>
<div>So is it a loop, is it a dipole, is it both, how can it be both, if=
 it is what&#39;s its radiation pattern ?</div>
<div>Similar to the ground loop/dipole question ?</div>
<div>=A0</div>
<div>And is there a length where the inductance of the loop bit resonates=
 with the capacitance that &#39;ought&#39; to be there due to its also bei=
ng=A0a short dipole.</div>
<div>=A0</div>
<div>?????????????????????????????????????</div>
<div>=A0</div>
<div>Andy<br><a href=3D"http://www.g4jnt.com/">www.g4jnt.com</a> </div>
<div>(not really an antenna sort of person)<br><br><br></div>
<div class=3D"gmail_quote">On 21 July 2010 08:12, John Rabson <span dir=3D=
"ltr">&lt;<a href=3D"mailto:john.rabson@numeo.fr">john.rabson@numeo.fr</a>=
&gt;</span> wrote:<br>
<blockquote style=3D"BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8e=
x; PADDING-LEFT: 1ex" class=3D"gmail_quote">
<div style=3D"WORD-WRAP: break-word">
<div>
<blockquote type=3D"cite">
<div>Reposted by permission</div></blockquote>
<div><br></div>John F5VLF<br><br>
<blockquote type=3D"cite">
<div>The antenna is a &quot;horizontal end-grounded line current&quot; ant=
enna;=A0commonly referred to as a &quot;horizontal end-grounded electric=
 dipole&quot;. =A0The word &quot;dipole&quot; is often used a bit too loos=
ely, although that is a=A0moot point. If you think &quot;horizontal electr=
ic dipole&quot; you get the=A0general idea: its an electric dipole, not a=
 loop antenna.<br>
<br></div></blockquote></div></div></blockquote></div>

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