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Date: Fri, 14 Aug 2015 17:52:26 +0100
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From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group@blacksheep.org, rsgb_lf_group@yahoogroups.co.uk
Subject: LF: Folded monopole - Food for thought
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On the RSGBTech group recently G3RZP described his folded monopole topband
antenna.  he runs an insulated wire up the side of the lattice mast to
which it is bonded at the *top*.  The bottom of this wire becomes the feed
point and requires a matching unit to tune out the residual inductance of
the resulting loop - plus impedance transformation..  The bottom of the
mast is grounded, and connected to a radial mat.

The advantage of this arrangement is it allows a conventional mast to be
used as a radiator.  The feed is nominally inductive, being a think
squashed loop, but the height of the mast stays what it would have been if
fed conventionally.  An HF beam and sundry other stuff on the top acts as a
capacity hat.

Disadvantages relate to isolation of cabling for equipment for other bands'
use, and needn't concern us with its use here.

I wonder if anyone has tried this scheme on MF or LF over the years/ (I
know topband is MF, but you all know what I mean :-)
Being able to feed a short monopole using capacitive tuning instead of a
conventional bulky, complex-to-build adjustable loading coil must have its
advantages.

It may also make for a quicker to put together portable of fast up- fast
down system, or ad-hoc antennas?

Some time ago one of the well thought out more rational arguments about
magnetic loop antennas was that when they become larger than "very very
small" , the linear dimension across the loop then starts to behave as a
dipole with appreciable addition to the true loop operation.    here we
have a loop, but deliberately elongated to enhance the dipole (or here the
monopole) behaviour.

Consider the ultimate limit, a tall twin feeder, shorted at the top and fed
at the bottom, with one side grounded.

An idle thought...

Andy  G4JNT

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<div dir=3D"ltr"><div>On the RSGBTech group recently G3RZP described his fo=
lded monopole topband antenna.=C2=A0=C2=A0he runs an insulated=C2=A0wire up=
 the side of=C2=A0the lattice mast to which it is bonded at the <strong><u>=
top</u></strong>.=C2=A0 The bottom of this wire=C2=A0becomes the feed point=
 and requires a matching unit to tune out the residual inductance of the re=
sulting loop - plus impedance transformation..=C2=A0 The bottom of the mast=
 is grounded, and connected to a radial mat.</div><div><br></div><div>The a=
dvantage of this arrangement=C2=A0is it allows a conventional mast to be us=
ed as a radiator.=C2=A0 The feed is nominally inductive, being a think squa=
shed loop, but the height of the mast stays what it would have been if fed =
conventionally.=C2=A0 An HF beam and sundry other stuff on the top acts as =
a capacity hat.</div><div><br></div><div>Disadvantages relate to isolation =
of cabling for equipment for other bands&#39; use, and needn&#39;t concern =
us with its use here.</div><div><br></div><div>I wonder if anyone has tried=
 this scheme on MF or LF over the years/ (I know topband is MF, but you all=
 know what I mean :-)=C2=A0=C2=A0=C2=A0 </div><div>Being able to feed a sho=
rt monopole using capacitive tuning instead of a conventional bulky, comple=
x-to-build adjustable loading coil must have its advantages.</div><div><br>=
</div><div>It may also make for a quicker to put together portable of fast =
up- fast down system, or ad-hoc antennas?</div><div><br></div><div>Some tim=
e ago one of the well thought out more rational arguments about magnetic lo=
op antennas was that when they become larger than &quot;very very small&quo=
t; , the linear dimension across the loop then starts to behave as a dipole=
 with appreciable addition to the true loop operation.=C2=A0=C2=A0=C2=A0 he=
re we have a loop, but deliberately elongated to enhance the dipole (or her=
e the monopole) behaviour.=C2=A0=C2=A0=C2=A0 </div><div><br></div><div>Cons=
ider the ultimate limit, a=C2=A0tall twin feeder, shorted at the top and fe=
d at the bottom,=C2=A0with one=C2=A0side grounded.</div><div><br></div><div=
>An idle thought...</div><div><br></div><div>Andy=C2=A0 G4JNT</div><div><br=
></div><div><br></div><div><br></div><div><br></div></div>

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