From: "Clemens Paul" <cpaul@gmx.net>
To: <rsgb_lf_group@blacksheep.org>, <rsgb_lf_group@yahoogroups.co.uk>
References: <CAA8k23TogtdhVt5L4N8h2X8mZQeqTnPR1VPydFpYQrHnTG3ojQ@mail.gmail.com>
In-Reply-To: <CAA8k23TogtdhVt5L4N8h2X8mZQeqTnPR1VPydFpYQrHnTG3ojQ@mail.gmail.com>
Date: Fri, 14 Aug 2015 21:20:49 +0100
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Subject: LF: RE: Folded monopole - Food for thought
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Hello Andy,

I seem to remember that NEC modelling done by a real expert in this area,
W4RNL (sk), years ago revealed that a 'linear' (ungrounded) monopole of the same height as a folded
monopole has a significant higher gain if the height is below 60 degrees (0.17 lambda)
(excluding losses in the matching circuitry).
But I've never modeled these antennas myself.

73
Clemens
DL4RAJ 
 

>-----Original Message-----
>From: owner-rsgb_lf_group@blacksheep.org 
>[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Andy Talbot
>Sent: Friday, August 14, 2015 5:52 PM
>To: rsgb_lf_group@blacksheep.org; rsgb_lf_group@yahoogroups.co.uk
>Subject: LF: Folded monopole - Food for thought
>
>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
>
>
>
>
>