Antenna design

My antenna is a center to top loaded vertical radiator.  It features a 3/4-inch ID copper pipe mast from trailer-hitch height to the bottom of the coil.  In theory the mast under the coil carries the most current and does the most radiating.  Everything from the coil up removes from the car but the mast and the steel support remain unless unplugged from the trailer hitch which can take a few minutes.  Since I no longer have a pickup with a storage cap I had to make the cage small enough to carry indoors.  Since this capacity cage is smaller than my previous version I tried to make up for the loss by making a more efficient coil.  The core of the top section is 5/8-inch fiberglass rod.  The entire assembly is ultra strong and rigid.  There is no motion of any of the antenna parts with respect to the car except for a few inches of whip above the cage.  This minimizes SWR changes as a result of motion.

The 75-meter coil is 9 inches in diameter and 6 inches tall.  There are 16 turns with 2 taps which allow for 40-meter or 60-meter operation.  Taps are selected using a flexible 1/4-inch braid jumper.

The cage is 19 inches tall by 16 inches in diameter and lives about 7 inches above the coil.

The mast (below the coil) is approximately 54 inches tall.  The overall height of the antenna is limited by the need to drive under low overpasses without tearing the antenna off the car.  The top of the cage is a few inches over 7 foot from the ground.

Note that for stationary operation the mast can be extended a foot or two by simply not sliding the top section all the way down.

The antenna impedance is under 9 ohms on 75-meters and under 6.5 on 40-meters

I use broadband transformers to impedance match.

The capacity cage

160-meter coil design

Antenna videos

 

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