Antennas Are Optional
Early morning finds me southeast of Calgary parked on a bluff that overlooks the river breaks bordering the Bow river visible from my position in this photo, although not from this angle.
This location is a terrific location for working mobile, and also would be a great location for field day as the location has commanding views to the horizon.
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 aluminum receiver 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.
Here is a closer look at the antenna....
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, no tuner required.
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 tig rods 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
I also changed the design somewhat so that the antenna breaks down to a 3' length overall, and I sourced a compact cordura case in the form of a spinning rod case with an hard insert that the antenna packs in to when disassembled.
As it is set up in the photo with the additional aluminum elements hanging at either end, it is set up for 17 meters.
Each pair of elements for the various bands are installed by pulling the hitch-pins located at either end of the 10 meter dipole and inserting the chosen band set as seen in this link photo with the 17 and 20 meter elements shown....
As you can see I still have access to the cargo bay with the tail-gate open, and when assembling the antenna, I can do that while standing on the tailgate which keeps the elements from dragging on the ground during assembly.
I also push the mast up while standing on the tailgate making it a simple and painless procedure.
How it all stores away in the cargo bay.....
Click on the photo for a closer look.....