40 Meter Dipole

 

Lacking trees for support and not wanting to string a conventional dipole(s) between towers where it would be amongst guy wires and possibly affect other antennas, I resurrected a couple of sections of an old commercial two element yagi that are one inch aluminum tubing with 7/8 X 5 inch fiberglass rod insulators in them.  The original coils and housings were damaged so they were discarded.  That provided the basis for my rotatable dipole that is mounted at 58 feet.

New coils were wound with #12 enameled wire wound on 1X 8 inch lengths of PVC.  The ends were slotted and SS hose clamps were placed with a resulting noticeable improvement in strength and less drooping of the element ends.  A leftover short piece of of Phillystrand used as a truss guy also helped relieve sagging and the forces at the mount.  I covered the coils with electrical tape, but six inch pieces of 1 1/2" black heat shrink tubing would be preferable.

 

The advantage of shortening the antenna physically with a lump inductive load is that the resulting bandwidth is very good and nicely covers the whole band.  That is not the case with linear loaded antennas I have used.  As well, had the antenna been full length, the center sections would have needed to be 2 inch tubing.

My guess is that the relatively close spacing of the coil turns will not be a problem unless I inadvertently dump a kilowatt of non resonant energy into it.

Dimensions

(each side)

Tubing diameter    Length

1.25"                    95.5"

1.125"                    30"

1.00"                    20"

Coil    1" X 5"    29 turns, #12 enameled, approximately 7pH

1.00"                    24"

.750                    32"

.625"                    7"

.438"                    38"

Total span with both sides and 2" separation at the feed point is 48 feet.