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

["Dick Rollema" <d.w.rollema@freeler.nl>]

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