Thursday, July 21, 2011

Simple Antennas for the Hawaii Ham, part 2

'Just a few more thoughts on simple antennas before I shut down the newsroom for the day and head to the qth.  In the previous post, I described an unsophisticated, basic antenna that could get you on the air quickly with a minimum of effort.  You can erect a simple 40-meter dipole with coax feedline in a variety of configurations, ranging from a straight dipole and inverted "vee" to a sloper and a vertical dipole (if you have a tall mast).  This basic antenna will work well on 40-meters and give acceptable service on 15-meters (using the 3rd harmonic of the 40-meter band).  I'm using one these simple inverted "vees" in my backyard and it does well for casual rag chews and interisland service.  My pvc mast is 33' high at the apex and the 33' dipoles go off at an angle, meeting two 5' stakes at either end.  I get reasonable interisland coverage as well as decent DX to the west coast of the U.S. mainland.  I believe there is a degree of  high angle radiation as well, giving me some good local coverage.  My primary NVIS antenna is the 40-meter loop strung under the house, which is elevated approximately 6-feet off the ground on a post and pier system. 

This bare-bones antenna can be pressed into multi-band service if one replaces the coax feed with 40-50 feet of twin lead (either 300 or 450 ohm).  Attach the twin lead to a 4:1 balun (DX Engineering makes several well-built baluns for a variety of applications), run a short length of coax (RG-8, 9913, RG-8X, or even RG-6 with suitable connectors) to your antenna matching device (tuner), and then connect the tuner to your rig.  You may have to experiment with the length of twin lead to keep swr low--I've found any length approaching a  half-wave length for your lowest band will often present loading problems and eratic readings.  The ARRL Antenna Book explains this situation and provides twin lead lengths that will make your tuner happy.  I replaced the RG-8 coax last night in my inverted "vee" and substituted some 450-ohm twin lead for the coax.  I can tune anywhere between 40 and 10 meters with ease.  I suppose there is some radiation from the twin lead, but that doesn't seem to bother the rig or the electronics in my home.  As with my other verticals, I can swivel the pvc mast to ground level, which presents a low profile to the neighbors and reduces the possibility of a lightning strike entering my antenna system.  Swivel systems can be found in the DX Engineering catalog.  This antenna is easy to erect and requiress no radial system.  I've had a difficult time creating a decent radial system, owing to the small size of my backyard.  In a pinch, I've used an elevated counterpoise system with my vertical antennas.  This arrangement works and presents a comfortable load for the tuner, but its performance is lackluster. 

None of these antennas will outperform a beam or a dipole 50' above ground, but they do work.  Considering my space limitations, I'm satisfied with my homebrew inverted 40-meter inverted "vee"-- a simple antenna that gets me on the air and provides hours of enjoyment at a minimal cost. 

Paging through my old antenna and log books, I'm surprised at just how effective these simple antennas are.  Of course, propagation plays a huge role.  Nonetheless, I've worked the world with verticals, inverted "vees", and loops.  You can do it as well.  For those of us on restricted budgets, a vertical made from locally obtainable resources could keep "you in the game."

May your log be filled with DX.  Aloha es 73 de KH6JRM.