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[Towertalk] Interlaced 15/20 Yagi

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Subject: [Towertalk] Interlaced 15/20 Yagi
From: (David L. Thompson)
Date: Wed, 1 Jan 2003 16:45:00 -0500
There was a great article (before most modeling programs) by W9LT (now also
WA7LT) on testing parasitic elements as refectors and directors.  Although
empirical, the summary shows that you must be careful with interlacing
elements.  The article was in a Summer 1976 CQ.

Long before, W3GRF found that to be effective and utilize the effect of
inefficient elements (behind) that you could put two or three bands on the
same boom if you put the 20 on the back, then the 15 meter elements, and
finally the 10 meter eleements.  He built and wrote about a long boom
tri-bander with 3 el on 20/15 and 10.   W4KFC used this design for his dual
band beams.

As N4KG pointed out you can take measures such as detuning an element so it
won't mess up the pattern.  Guess it boils down to big tri-banders where
each element covers all three (or more ) bands,
using the Sommer design where the antenna is NOT a yagi (they are phased
elements with an entirely different set of interaction problems), or going
Mono Band (best solution).  Otherwise settle for the interaction of
interlaced beams.  However the interaction can be minimized with proper

As for me and my one tower its a no brainer a big tri-bander and a 2 el 40.
I am too old to swap out the tri-bander for a big single band beam as I did
years ago.

73 Dave K4JRB

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