Simon
When you posted your original information request for advice concerning
interlaced 20/15 yagis, I noticed you stated that you could not accommodate a
boom
much longer than 16 feet. Evidently few others noticed this restriction as
most of the postings to the reflector advise you to consider the 48 foot boom
OWA design by WA3FET.
While the WA3FET design is interesting, the text accompanying the specs which
details the reason he chose to mount the 15 meter portion of the antenna
entirely ahead of the 20 meter reflector and driven element is must reading for
anyone who entertains building an interlaced 20/15 yaig. The actual OWA design
with its 48 foot boom may not be suitable considering your restrictions,
however, the information about interlaced performance he (WA3FET) reports in
his
write up will explain why it is a challenge to build an interlaced yagi for
20/15
on a boom as short as you desire.
My 20/15 interlaced yagi (26 foot boom, 3 on 20, 4 on 15 at 24 feet) performs
very well on 20 meters but seems to suffer some of the problems WA3FET
describes on 15 meters. WA3FET claims that the 20 meter section of the
interlace
will probably not see any detrimental effect of being interlaced with the 15
meter portion but, that the 15 meter portion will suffer if not placed ahead of
the 20 meter as with his design. The very same design for 15 meters was used
(and scaled) in building my 10 meter monobander. The 10 meter monobander
performs
like magic, the 15 meter portion of my interlace always seems a bit below the
performance I would expect.
I believe you will find that you really cant build much of an interlaced
20/15 on a boom as short as 16 feet if you follow WA3FET's advice. You may want
to
resort
to a classic 3 element tribander with a 16 foot boom. Another alternative
that might work well for you is a triband quad.
Ron KH6DV (KH6VV)
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