[Lf] RE:Aerial info etc.]

[Andre' Kesteloot]

Talbot Andrew wrote:

> The equation for capacitance of a wire above a groundplane, as given in
> any textbook of electromagnetism, includes a term  LOG(diameter) so
> there will be diminishing returns on wider spacing .  Capacitance is
> proportional to length, so it looks as if for a given amount of copper,
> length will win over multiple parallel wires any time.   OK for those
> with decent sized gardens.........
> As for the actual ground loss, I rather like Laurie's shower head
> analogy, it sort of makes intuitive sense.
>
> Still does not answer why my tiny antenna system has ONLY 100 ohms loss
> resistance, compared with some other much bigger systems described here
> with higher values than this.
>
> Andy  G4JNT
>
> > ----------
> > From:         LAWRENCE MAYHEAD[SMTP:LAURIE at g3aqc.freeserve.co.uk]
> > Reply To:     rsgb_lf_group at blacksheep.org
> > Sent:         2000-08-04 08:41
> > To:   rsgb lf group
> > Subject:      LF: Re. Aerial info etc.
> >
> > Hi Alan,
> > "Whoops" looks like I have mis-lead you!
> > The 700uH does not resonate the Ant.,I need another 1mh at the base to
> > do that.
> > When the top inductor is not in use the base inductance is about
> > 1.6mh.This gives a total capacity of 855pf. Rik Strobbe gives some
> > useful figures for the cap. of vert and horiz wires,about 6pf/m at 15m
> > height,so allowing about 100pf for the vert part this leaves 755pf.
> > So.755/6=125m. This probably about right since my top wires are close
> > together at times and not all the 160m are effective.I have used Eznec
> > to model my Ant.and it shows that the current in the vert. section is
> > almost constant(drops from 1A down to 0.97A at the top) so the
> > effective height of the Ant. is almost equal to the actual height.So
> > there is not much more to be gained in this area which is why the top
> > inductor was ineffective,with less cap. loading I am sure it would
> > have been useful.
> > I still wonder wether there scope for a further reduction in loss
> > resistance by putting in more top wire ?or is there a law of
> > diminishing return here also.I would also like to investigate wether
> > its better to have one long topwire(doesnt matter if its bent) or
> > wether several wires in parallel.would be as effective.But this must
> > wait,unless someone else can do the experiment!
> > Finally I agree about the 10ft radial but I am sure there is more to
> > it than this,we come back to ground penetration,"shower heads" etc
> > .73s Laurie.
> >
>
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