[Lf] [Fwd: LF: Re: Re: Ant Questions]

[Andre Kesteloot]

"Holger 'Geri', DK8KW" wrote:

> 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 at ntlworld.com>
> To: <rsgb_lf_group at 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
> > ====================
> >
> >
> >
> >