Inverted U Rotatable Field Diople
I wanted to build an antenna to mount on my Max-Gain Systems push-up mast, that I mount on the back of my mobile on the new aluminum receiver antenna mount adapter that I built recently.
Looking through the various antenna books that I have in my library I came across a design by L.B. Cebik W4RNL that peaked my interest, the Inverted U rotatable field dipole.
So what your seeing here is my version of the Inverted U that covers the bands of 10, 12, 15, 17, and 20 meters and is a 1/2 wave dipole on all bands.
A dipole’s highest current occurs within the first half of the distance from the feed point to the outer tips. Therefore, very little performance is lost if the outer end sections are bent. The W4RNL inverted-U starts with a 10 meter tubular dipole. You add extensions for 12, 15, 17 or 20 meters to cover those bands.
I took liberties with the design and changed a number of things that I felt could be improved on, one being the wire elements that attach to either end of the 10 meter dipole allowing for band changes to 12, 15, 17, and 20 meters.
I made the elements from .093 diameter 4043 aluminum rods 3' in length that are fastened together through a unique hinging system that allows the various band elements to be quickly deployed once they are attached with hitch-pins to the either end of the main 10 meter dipole.
Another area that I made changes is in how the antenna mounts on the 1" top section of the push-up mast. I turned and bored a 1 1/2" X 4" piece of Delrin that is part of the center section of the antenna that allows for quickly mounting the antenna in place on the mast.
Drop it on and insert the locking pin through the mast and its done
Not shown in the photo are the hitch-pins that are used for locking the telescopic sections of the dipole together.
I also changed the design somewhat so that the antenna breaks down to a 3' length overall, and I sourced a compact cordura case (as seen in the photo) with an hard insert that the antenna packs in to when disassembled.
Click on the photo for a closer look.....
Here is the antenna up top of the push-up mast in the field.....