VE6AB Mobile Ops
Bigger Antennas Perform Better
When it comes to mobile HF antennas, bigger is better.
The HF antenna on the back of my mobile as seen in this photo stands 13' 6" off of the ground.
The antenna by itself measures 9' in length from the base to the tip when measured from the deck on the back of my mobile where it is mounted.
A half-wave 80 meter dipole measures approximately 130 feet in length.
So you see why mobile HF can be somewhat challenging, and why size counts when it comes to the HF antenna you run on a mobile.
I designed my gearmotor antenna to cover the bands from 10 to 80 meters, although with the whip and caphat shown mounted on the antenna, it will only allow the 17 through 80 meter bands to be worked.
When I wish to work the 10, 12, and 15 meter bands, it is required that I change out my whip and caphat for my optional 6' steel whip (without a caphat) that allows these bands to be worked.
This whip assembly is built from fiberglass covered in 304 stainless-steel mesh and terminated at the top with a 36" diameter 3 petal 304 stainless-steel caphat.
Running a caphat at the very top of the whip is the best way of increasing efficiency in a mobile HF antenna.
The caphat added to the top of the antenna makes the antenna appear electrically larger by adding capacitance to the antenna and the more capacitance you add to the antenna, the higher the radiation resistance, and the higher the efficiency of the antenna.
So remember...."Bigger is better when it comes to mobile HF antennas."
Click on the photo for a closer look.....
HF Mobile antenna installs....
http://ve6ab.blogspot.ca/2015/07/hf-mobile-antenna-install.html
