Topband: Length of 'T' Top Hat wires?

[Joe Subich, W4TV]

 > If I mis-interpreted the rule, I like to know what it means.

Many times the top hat wires are not horizontal but come down at an
angle like the top set of guy wires on a tower or vertical.

 > Is there any theory to the "25% rule"?

The 25% rule says the ends of the top hat wires should not extend
more than 25% down the vertical.  The thought is that the wires
"shield" the main vertical ... that the currents on the top hat
wires cause cancellation.  Once the tips of the top hat wires get
25% down the vertical, the theory is that the cancellation/reduced
radiation resistance offset any gains from the added electrical
"height."

N6LF made reference to this phenomena in one of his studies -
unfortunately I don't have the link at hand but Rudy's site
is well worth exploring.

73,

    ... Joe, W4TV


On 12/13/2012 11:37 PM, Ray Benny wrote:
> I have a 67 ft base coil fed vertical, 4", 3" & 2" irrigation pipe with two
> 50 ft top hat wires that I use on 160m. I have about 100 - 135 ft radials
> on the ground. So far I have been pleased with it.
>
> Last week Herb, KV4FZ mentioned the "25% rule", which I think means, the
> top hat 'T' wires should be cut to about 25% of the vertical height. I have
> not heard of this rule and wonder how it may have come around?
>
> I can certainly shorten my top hat wires to abt 17 ft, then re-tap the base
> loading coil to bring the SWR and resonate point to 1.830 Mhz or so but I'm
> wondering if its worth it?
>
> Is there any theory to the "25% rule"? If I mis-interpreted the rule, I
> like to know what it means.
>
> Tnx,
>
> Ray,
> N6VR
> Chino VAlley, AZ
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