Re: Interaction of tribanders and 40M Beams de N4KG
One approach to reducing interaction of stacked Yagi's
is to rotate one of the booms 90 degrees to other antennas.
This may or may not eliminate interaction problems.
Remember, BOOMS are NOT invisible.
A 24 ft Boom, end loaded by 20M elements (or tribander elements)
has a self resonance very close to 40M. As a result, a TH7 boom
for example, may act as a 40M director, directly above or below your
40M beam, reducing both gain and F/B in the desired directions
by skewing the antenna pattern upward or downward depending
on the exact resonant frequency of the loaded boom and the
relative antenna placement.
Many low banders have utilized this near resonance on 40M to
match the booms of their tribanders or 3L20 meter beams as
rotary dipoles on 40M.
With parallel booms, it makes sense to also match the boom
of your tribander (with non-insulated elements) as a 40M
rotary dipole. Then it is a simple matter to merely switch from
the 40M beam to the 40M boom dipole to catch stations at
90 degrees to the beam such as SA / Carib when beaming
Europe, or VK / ZL when beaming JA.
de Tom N4KG
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