Message-ID: <008701c32430$b375d560$0100a8c0@athlon>
From: "Dave Brown" <tractorb@ihug.co.nz>
To: rsgb_lf_group@blacksheep.org
References: <OFBA14FF20.7902AF99-ON89256D32.00648E85@ppco.com>
Date: Tue, 27 May 2003 21:16:46 +1200
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Subject: LF: Re: Top loading - to short or not to short?
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I believe you will find the multiple vertical wire arrangements are
generally for mechanical stability and don't have a lot to offer
electrically. As amateur top loaded antennas are generally a lot smaller
than the commercial ones (There are some exceptions!) they don't need these
considerations. A large two wire flat top for example, typically has
stabilising halyards from each end of the spacers down to a comon anchor
point at both ends of the flat top and in the middle-. The ones in the
middle do double duty as the vertical element as well but will usually be
commoned some distance above the top of the loading coil structure so a
single wire forms the lower portion of the vertical element. Conversely, the
end halyards are usually tied down to an anchor point on the support masts
individually, so they can be adjusted individually as required. ( to keep
the flat top flat!)
73
Dave, ZL3FJ

----- Original Message ----- 
From: "Laurence J Howell" <L.Howell@conocophillips.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Tuesday, May 27, 2003 6:55 AM
Subject: LF: Top loading - to short or not to short?


>
> Im  still struggling with a 110 foot dying spruce tree and wonder if Ill
> every get the wire up it before it snaps in these high winds. Spruce trees
> are dying/have died in large numbers in S central alaska. Beetle carrying
> virus.
>
>   In looking at my LF Inverted L, and specifically the 3 wire top loading
> wires - I've a couple of questions...
>
> 1. I see a recommendation that the vertical part of the Inv L aerial
> wire(s) should be a single wire (ZL recommendation), or if not then three
> or how many wires should converge to a single point at the bottom. Why is
a
> single wire recommended over  a multiple? Em thinking losses into nearby
> objects? Wouldn't a multiple vertical wire feed increase  "good non lossy"
> C and increase Ra?
>
> 2. Ive seen a large amount of schematics both for commercial and ham top
> loading.of T and L's ...Say for a three wire top loading spaced 1m apart -
> should the wires at the far/near end all be shorted together or left open?
> Does this affect the total cap either way, or is it just for electrical
> "circuit" stability?? Does it make any difference if they are shorted at
> any point along the top?? Is there a recommendation which proves open
> versus short is better ?
>
> Mine are open all the way and Im using a converging 3 wire vertical wire
> feed... I see shorted at the ends, shorted half way, open ended solutions
> from my peers here...
>
> Im trying to rationalize that the end of the loading wires are at Zero
> Current (no different circulating/local currents between the wires?).. and
> it may not be an impedance thing but may help reduce high voltages as the
> surface area at the end is now a lot larger...and may reduce corona.
>
> Most commercial T's for NDB short out at the far ends..and I do see single
> and multiple wire converging vertical wires, so I guess they are all right
> But a lot of the drawings ref materials show them open! Arghh.
>
> Any experiences welcomed...
>
> Laurence KL1X -
>
>
>