Asymmetrical Hatted Vertical Dipole AHVD 20 - 40M
I have a Bravo 5A that covers 10, 12, 15, 18, and 20 meters. The Bravo 5A is similar to an Asymmetrical Hatted Vertical Dipole. You change bands using a wired remote switch and power supply at the ham shack. The remote switch changes inductance via relays at the base of the antenna. The Bravo 5A works fantastic and takes 5 minutes to setup in my backyard.
The Bravo 5A works very well, that I wanted to purchase a Bravo 7KR for 30 and 40M. Unfortunaltely I could not find one to purchase, so I decided to fabricate an AHVD myself.
The AHVD antenna I built is in the picture above. It consists of a vertical element, two horizontal elements, and a matching base. The vertical wire is held up with a 16.5 foot crappie fishing pole and the horizontal wires are strung between the fence using nylon string. The horizontal wires are about 60% of the length of the vertical wire. The crappie pole end fits over a 5 foot 1/2 inch dowel. The base is the XYLs umbrella stand Hi Hi.
The matching base is depicted above. The vertical element is attached to the outside of the enclosure with the top right screw, and this screw is also used for the 40 meter vertical coil. The two horizontal elements are attached to the outside of the enclosure with the top left screw, and this screw is also used for 40 meter horizontal coil. At the bottom, the antenna coax is attached to the outside of the enclosure with the two lower screws. The same screws are used to attach the 20 meter coils. The two middle coils are for 30 meters.
The alligator clips are used to switch between 40, 30 and 20 meters. The coils for the higher hands are added to the lower band coils to provide the correct inductance. In the picture above the alligator clips are not used allowing all of the coils in series to resonate the antenna on 40 meters. If the two alligator clips are moved to the second from the top screws, the antenna is resonate on 30 meters because it is bypassing the 40 meter coils. And finally if the alligator clips are moved to the third from the top screws, the antenna is resonate on 20 meters. When fine tuning the AHVD to each band, you compress or spread out the coils. Start with 20, then 30, and finally 40 meters
The impedance of the AHVD is very low, so it requires a matching circuit at the feed point. I am using a Swan MMBX Antenna Match Box. You can also use a hairpin match, but I found that each band requires different size.
In regards to the AHVD performance I am impressed. I am able to work NAQCC stations I hear during our sprints with my KX2 @ 5 Watts. Given I am in a HOA, I only use a maximum of 30 Watts on my other rigs and I am able to work DX. I now need to figure out how to build an 80M antenna for my post stamp lot :)