Ron, thanks for the advice - it is an interesting topic, of which there
seems to be little information on the web when it comes to short boom
interlace designs. I take your point with regards to the higher frequency
elements being better placed in front of the lower ones to achieve best
performance overall ie as in a forward stagger design.
All the information I have received seems to say that a short boom 3
element 15/20 interlace is difficult to achieve, although I notice that
there are some designs available commercially that utilise open sleeve
feeding that get by with quite short booms, albeit that they appear to
offer 2 element performance.
Because of the space limitations I have, I will stick with the antennas I
have made which are waiting to go up; a 15m 3 element monobander (design
from Mr Cebik's web site) and a home built inductively loaded 20m 3 element
(designs from various sources, cobbled together !).
I am assuming that I should space the two antennas at about half the boom
length of the lowest frequency antenna, this would equate to a six feet
space with the 15m antenna over the 20m. Can somebody tell me if I am wrong
in this assumption ?
Would love to be able to put up a five band 2 element quad , but again I
don't think my landlord would agree with me as to the beauty of such an
installation ! (I guess it's true what they say about beauty being in the
eye of the beholder)
Simon - Indonesia
At 04:28 PM 7/3/03 -0400, KH6DV@cs.com wrote:
>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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>
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