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Re: LF: Top loading - to short or not to short?

To: [email protected]
Subject: Re: LF: Top loading - to short or not to short?
From: "Dick Rollema" <[email protected]>
Date: Tue, 27 May 2003 09:38:54 +0200
In-reply-to: <[email protected]>
Reply-to: [email protected]
Sender: <[email protected]>
To Laurence and All,

Laurence,  KL1X wrote:

  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?

The antenna current returns to ground via the capacitance to ground of the vertical and of the top load .
Because we want the current in the vertical part to stay as large as possible over its whole length it is best when  as little current as possible flows from the vertical part to ground. So the capacitance of the vertical part should  be small as compared to the capacitance of the top load.Therefore a single wire is to be preferred.

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 ?

Because the voltage on parallel wires of the top load is the same at neighboring positions a connection between those points will carry no current and therefore has no use. 

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.

The corona argument is certainly valid.

73, Dick, PA0SE
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