[TowerTalk] 2m yagi installation

[Tom Hammond]

>I am installing a 2m yagi for local nets/emergency ops onto the top of
>my stack and would like to mount it vertically for proper polarization,
>but am wondering if the metal mast will interfere with it's properties?

Guaranteed that it WILL.

Years ago, I did just that very same thing... and used the 2M antenna
(a 10L yagi) for about 4 years, but with only mediocre performance.
Then, for some reason, I decided to off-center mount the yagi, to see
if I WAS actually experiencing problems from the in-plane mast.  I
added a 3' long horizontal mast to the mast from the rotator, and then
attached the 2M yagi about 2-1/2' out on the horizontal mast, the
yagi was still oriented vertically.  The difference in performance
was astounding, probably 10dB OR MORE (as measured by a 2+ S-unit
increase in received signal strengths).  Note that at the same time
as when I moved the yagi, I also moved the COAX out of the plane of 
the yagi elements as well.

>Should I try to change over to a fiberglass mast above the beam or does
>the polarization really matter with 2m after a short distance?

Fiberglass works well, but it's probably easier, and possibly lower
cost to just add another boom-to-mast mount (made of a 5" x 5" x 1/4"
piece of aluminum plate and 4 U-bolts) and a short (3') horizontal
mast, and side-mount the 2M antenna.

This addition shouldn't materially unbalance your array, unless the
2M antenna is really heavy.

73, 

Tom Hammond   N0SS

73 - Tom Hammond   N0SS

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