Message-ID: <000d01c26dd1$fe11b140$fe78a8c0@W1KW>
From: "Holger 'Geri', DK8KW" <holger.kinzel@qru.de>
To: rsgb_lf_group@blacksheep.org
References: <B7EAE54BB323844E9422FADCFAC1C4C34A55@orion.bikerz.local> <000c01c27787$566bf080$1b6868d5@oemcomputer>
Date: Mon, 7 Oct 2002 09:20:16 +0200
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Subject: LF: Re: Re: Ant Questions
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Hello

>Do not be tempted to droop
> the ends of any top wires.

... I challenge that. My umbrella antenna 18m high with 5 pieces of top-load
radials sloping downwards (each about 7 m long) works fine (see sketch at
http://www.qru.de/station.htm), with an antenna "gain" of roughly - 30 dB.
One of the key factors that had increased my ERP was to put up my loading
coil 1/3 way up the fiberglas mast so that any losses occuring due to high
voltages due to surrounding trees and walls are reduced.

Best 73

Geri, DK8KW (W1KW)


----- Original Message -----
From: "mike.dennison" <mike.dennison@ntlworld.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Saturday, October 19, 2002 5:50 PM
Subject: LF: Re: Ant Questions


>
> G0CZD wrote:
>
> >I'm about to put up a 136kHz Antenna and have a couple of questions.
> >I don't have much space in the garden, approx 20m from the apex of the
> roof to a 20m high poplar tree in the opposite corner. I am considering
> an offset 'T' with a multi-wire top.
> >I am assuming (within practical limits) that as much capacitance as
> possible in the antenna is beneficial. It will resonate with lower
> inductance and therefore lower resistive losses.
>
> Yes, that is correct.
>
> >The RSGB LF experimenters h/b (p52) suggests that 2 wires separated by
> >100mm will provide 39% increase in capacitance. Is it safe to assume
> >that putting multiple wires up at 100mm will provide a compound
> >percentage increase? I am considering 6 wires at 100mm separation. Are
> >there any better solutions - I have neighbours I wish to remain on
> >speaking terms with...
>
> The capacity hat should be as wide as possible. This is more important
that
> many wires. In fact, you quickly get into the law of diminshing returns
with
> extra wires, plus the weight increases much faster than the capacitance. I
> use three wires over a total width of 1m. Making it wider would be better
> than having extra wires.
>
> >What effect does height have on the antenna? I can fairly safely get the
> >antenna up to 10m above ground level without too much difficulty. Will
> >there be any significant benefit to raising the tree end of the antenna
> >to say 15m.
>
> Yes. Height is all important as the ERP is directly related to the
=square=
> of effective height. Effective height varies from 50% to 100% of the
actual
> height depending on how good the top section is. Do not be tempted to
droop
> the ends of any top wires.
>
> Good luck, Martyn. If you need to see a sketch of my antenna, which is 14m
> high by <18m long, it can be found at my web site.
>
> 73
>
> Mike, G3XDV
> http://www.lf.thersgb.net
> ====================
>
>
>
>