> 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
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Administrative requests: towertalk-REQUEST@contesting.com