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[TowerTalk] optimum height

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Subject: [TowerTalk] optimum height
From: (Tom Rauch)
Date: Sat, 28 Jul 2001 19:10:20 -0400
Hi Tom,

> A  FULL  Wavelength on 40M is 140 ft.
> A HALF WAVE Dipole is 66 ft allowing ~5% for end effects.
> A 47 ft boom is .335 WL.  The square root is .58  sq rt WL
> (whatever the ***? those units represent).  If we accept that
> the units should be WL, that corresponds to 81 ft which is 
> close to optimum.  Actually, stacked 2L40's exhibit peak 
> gain when stacked at 80 and 160 ft.

But that's true even when the booms are only 5 feet long with two 
elements, or if they are 50 feet long with three elements! 

As a matter of fact, it is true if they are dipoles with no boom at all! 

It seems a more accurate rule of thumb would be a minimum of 
5/8th wl separation, and then some other number mixed in as the 
antenna becomes more directional. One problem would come if 
ground reflection happens to force a null where stacking spacing 
forces a null. In that case there would be minimal gain.

Whatever anyone does, they certainly should model the antenna. I 
think that is the main point.
73, Tom W8JI 

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