Thursday, April 26, 2012

Simple Antennas for the Hawaii Amateur Radio Operator--a continuing series

Do you remember your first amateur radio antenna?  I certainly do.  It was ugly, fed by cheap RG-58 coax, and connected to my first rig, the Heathkit HW-101.  I called it a dipole only because each side of the Budwig connector had 33-feet of 20-gauge wire attached.  The ends of this homebrew skyhook were attached to two trees about 35-feet high in the back yard of the teachers' cottage near the Honokaa High School.  That was 36 years ago--a time long gone except for my memory of many contacts as a novice and techncian class operator.  I surely had fun with this crude antenna.  It was home made and it was my own.

Now jump forward to 2012.  I've been a general, advanced, and extra class ham since those glory days 3 1/2 decades ago.  I've gone through many rigs (most of them second-hand and well-used) and several types of antennas.  Yet, I still haven't lost the excitement of those novice class days.  For me, designing and erecting antennas are still fun, educational, and worth the effort.  I suppose a commercially made antenna would have solved many of my signal problems as a new novice, but I enjoy getting my hands dirty, measuring out the wire, strapping pvc pipe together, and seeing if the antenna project will endure Hawaii's sun, rain, and volcanic smog (vog).  Those three elements can destroy an antenna in a few short years.  In fact, the acid rain that falls here (caused by the active Kilauea Volcano) really damages the paint on most vehicles.  I'm constantly polishing my van to keep rust, soot, and corrosive materials off the vehicle.  It's a continuous battle against the elements.  The same applies to antennas.  That's why I keep my antennas simple.

Over the past few years, I'v found simple dipoles fed with 450 or 300 ohm twinlead seem to do the best as general purpose HF antennas.  I've been fortunate to have access to various lengths of schedule 40 pvc pipe which can be used to make 25-35-foot masts.  This lightweight material can be erected by one or two persons fairly easily.  Once the pvc and its attached antenna wire are suitably guyed, they will serve nicely for a couple of years before nature takes her revenge.

I usually don't worry about the type of wire for the verticals I make.  Number 14-gauge house wire is abundant, as are smaller gauges such as 20, 22, and 24.  As long as the small wire is supported by and taped to the pvc mast, it will serve as a decent antenna.  Then all you have to do is attach a number of radials and you're on the way to enjoying amateur radio at a fairly cheap price.  One can also use a mast to make an inverted "vee" which doesn't require a radial system.  I've used both types of antennas on my small lot. 

As for coax, I've found RG-6 (the type cable companies use) and RG8x quite satisfactory for low power applications below 50 watts.  When I worked at a commercial radio station in Hilo, I was able to get various lengths of RG-6 from studio rebuilds.  I've used these various lengths to make patch cords and feedlines.  Even if you have to buy RG-6 from a hardware store (such as Home Depot or Ace Hardware), it's a good bargain.  You can order adapters for the "F" connectors from a variety of cable distributors.  With an approximate impedance of 75 ohms, RG-6 shouldn't be too difficult a match for your antenna tuner.  My Drake MN-4 seems to do alright with this cable.  For higher power levels, you may want to use RG-8 or RG-213.

My xyl is right--I'm a packrat when it comes to electronics.  I haven't changed much since I was first licensed.  Only this time, I'm somewhat better organized.  At least all my wire, cable, parts, and tools are segregated by type and labled so I can find stuff quickly.  My garage is becoming a well-organized graveyard for leftover cable, wire, rigs, and reference material.  The ham who called his operating position a "shack" really hasn't seen my place.  It's what I call my overgrown "junk box."  My poor xyl has given up trying to "reform" me.  At least I can fix most electronic stuff in the house.  I suppose I do have my uses.

So, as we face another beautiful weekend on Hawaii Island, it seems appropriate to rebuild the dipole antenna I first used as a novice.  There are two medium high trees in the back yard with just enough room to string up a dipole with 32-feet on each side--a little short for 40 meters, but the 450-ohm twin lead, a 4:1 balun, and the trusty Drake MN-4 should be able to handle my excursions on this band.  Who knows? I may just leave it up for awhile...at least until the neighbors start asking questions.  If that happens, up go the verticals again.

Until next time, enjoy the weekend and get on the air!

Aloha es 73 de KH6JRM--BK29jx15.