[TowerTalk] 2 el. 40 shortie design

[Dan Levin]

Joe,

I designed and built a rotatable dipole for 40 meters that was
about what you want.  I used ~35' elements (about full size 20
meter length), with 6' diameter 8 spoke capacity hats with
a perimeter wire.  The elements were built according to the
20 meter taper schedule in the Antenna Book, heavy duty version.
The hats were made from .177" aluminum rod - four 6' pieces.
I sourced the tubing and rod from Texas Towers - great guys!
I drilled through a short (4") piece of aluminum tubing that
was sized to slip over the element tip in four places.  Then
I slipped each rod through to the middle, and brazed them
in place using a propane torch and some of the new low temp.
aluminum brazing (they call it "welding") rod.  Then I brazed
aluminum wire to the ends of the rods as a perimeter wire.

It played great!  I later built a 2 element yagi using similar
techniques, but longer elements (~50').  That yagi (which is
still up), uses 4 spoke capacity hats with no perimeter wire.

You want about a 24 foot boom, for decent feed impedance.  Use
a hairpin coil to step it up to 50 ohms - it will be less due
to the short elements.

GL es 73,


                  ***dan, K6IF

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