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[Towertalk] 100M-long boom Yagi for 20M

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Subject: [Towertalk] 100M-long boom Yagi for 20M
Date: Sun, 12 Jan 2003 00:09:38 -0500

     I was going through some old mags in the basement today and found a
couple of articles of interest (I hope) to TowerTalk related to Yagis.  They
are both from the June 1991 issue of IEEE's Antennas and Propagation

     The first, A Modern Giant Yagi, was written by W6TSW, W6VPH and K6BLG.
It describes their work on a 13-element, 100-meter long boom (!) Yagi for
20M.  The Yagi was constructed on six colinear towers on a hilltop in
Southern California.  The top guy set of each tower is dielectric material,
according to the authors.  One tower supports what looks like a wide-spaced
three-element 20M Yagi - Refl/DE/Dir 1 of the array.  Each of the remaining
five towers supports a wide-spaced 2-element Yagi (Dirs 2-11).  The photos
show all of the booms pointing in the same direction.  The plane of the 13
elements (tower height) is said to be 25M AGL.

     Specs are:  fixed azimuth of 15 degrees east of true North (don't
start!), covering selected portions of Europe and Asia; design freq: 14.150
MHz; predicted directivity: 15.8 dBi freespace/21.5 over low conductivity
ground; 3 dB beamwidth: 15 degrees either side of boresight.  Each element
is built with heavy wall Al tubing, starting with 32mm diameter, stepped
twice, and ending with 19mm at the element tips.  Each of the six,
75mm-diameter boom segments measures 9M long.  On-air reports of this
behemoth vs a wide-spaced 5-el Yagi support the calculated performance

     The second article is A Secret Story About the Yagi Antenna, written by
Prof Gentei Sato of Sophia University, Tokyo.  The article recalls his quest
to locate Newmann's Note, a set of papers reportedly recovered from a
burning trash pile after Japan's conquest of the British fortress in
Singapore in February, 1942.  It was from these notes, written by British
POW Newmann (variously identified in the article as Private, Corporal or
Master Sergeant) that Japanese engineers and military staff first learned of
the Allies' effective use of the Yagi antenna in RADAR.  Up until then, the
Yagi-Uda antenna, invented in Japan in 1926, had been used by the Japanese
in only two radio links to connect two off-shore points to the mainland.
The author comments that he himself learned during a visit to the
Smithsonian Institution in DC the the two atomic bombs that devastated two
of his country's cities included Yagi antennas as part of the
altimeter/detonation circuit.

     I found both of these articles to be a fascinating and colorful bit of
background on an invention that we TT'ians almost take for granted - the
venerable Yagi-Uda antenna.

73 de
Gene Smar  AD3F

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