[TowerTalk] 10/15/20 M yagi and 12/17 M yagi minimum stacking distance on a common mast

[Julio Peralta]

Some time ago I wanted to stack the CC A3S and the A3WS, I contacted CC and
one of their techs advised 11 or 12 feet was the minimum distance for good
performance. I stacked them at 12 feet and as far as I could tell they
worked fine like that.

Julio, W4HY

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of
rwhitetexas at verizon.net
Sent: Thursday, July 24, 2008 10:22 PM
To: towertalk
Subject: [TowerTalk] 10/15/20 M yagi and 12/17 M yagi minimum stacking
distance on a common mast

I have a CL-33 (18 ft. boom weighing 42 lbs.) up on a HDX555 and want to
stack on the same mast a 12/17 meter 3 element yagi above it. The 12/17
meter yagi is a Cushcraft A3WS with a 12 ft. boom weighing 23 lbs. I would
like to know the minimum distance I can mount the 12/17 yagi above the CL-33
before I start to adversely degrade the performance of both yagis. I am not
looking for peak overall performance, but do not want to have a situation of
too small a distance that will adversely effect both yagis performance. My
two favorite bands of interest are 15 and 20 meters once the sun spots
cooperate in a few years.

Is 1/2 the boom length of the higher freq antenna (12/2 = 6 ft. ) the
correct distance? I want to minimize the length (weight) of the steel mast
on top of the tower, so if I can have a shorter distance than 6 ft. between
the yagis and still have reasonable gain, then I would go with a shorter
distance.

For a 6 ft. distance between the yagis, the mast would be 10 feet
approximately (with 4 ft. from rotator to top of tower). That is about the
most I want on top. I usually leave the tower at 50 ft. high to have more
overlap than what it would have at 55 ft., thus giving me a little more
safety margin to handle the high winds we have in our North Texas
thunderstorms.

Roger W5RD
Murphy, Texas
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