Friday, June 15, 2012

Simple Antennas for Amateur Radio Operators--a continuing series


While I was reading the 13th edition of the ARRL's "Hints and Kinks for the Radio Amateur (copyright 1992),"  I came across an interesting article by J.A. Ciciarelli, WB3DDM, on strain relief for coaxial cables.  It wasn't the excellent suggestion of using garden hose or automotive heater hose to reduce strain on the coax that caught my eye,  but rather the type of antenna he chose for his operation.

Apparently, WB3DDM prefers to use long-wire antennas in the inverted -vee configuration.  According to J.A., " I feed the antennas 1/4 wavelength from one of  the leg ends so that I can use coax transmission lines (each leg is an odd multiple of a 1/4 wavelength).  Thus, the feed point is not at the apex, but along one of the sloping legs.  This arrangement frequently creates a sharp bend at the coaxial connector."  And so enters his idea of using hose to relieve some of the strain.  The process is illustrated on page 7-8 of this edition.

Anyway, I decided to apply his idea to a 20-meter antenna I was trying to design.  Although I had good performance with the vertical 20-meter dipole, I wanted to try something else.  Since I had about 50 feet of RG-6 with suitable connectors in the shack, I thought it might be a good idea to erect a long-wire 20-meter inverted - vee where the old vertical dipole used to stand.

I measured out 66 - feet of # 14 gauge hosehold wire and attached a Budwig coax connector to 16  1/2 feet of wire and strung the remaining 49 1/2 feet through the top of my 31-foot mast and then down to an anchor stake near the front yard.  The orientation was generally NNE, which gave  me a bit of gain to the U.S. mainland and Europe from my Hawaii Island location.

The Drake MN-4 ATU seems happy with the arrangement, since the tap is at a low impedance point and the remainder of the antenna is about 3/4 of a wavelength on 20-meters.  Reports have been good with the old Swan 100 MX running about 25 watts or so. 

Since the mast and wire are painted a dull green, the antenna is barely visible from the street.  As is my usual practice, I lower the antenna when I'm not using it--good protection from wind, storm, and curious neighbors.  I may try this idea for 15 and 10 meters.  The 40-meter vertical with tuned counterpoise (the "upper and outer" antenna described by the late Lew McCoy) will stay as my main 40 to 10 meter antenna.  I feed this creation with 450-ohm balanced line into a 4:1 balun and then run RG-6 to the Drake MN-4.  The Drake MN-4 seems happy with this arrangement.  The under-the-house 40-meter loop continues to serve as an emergency and local net antenna.

I'll keep you posted on my newest 20-meter skyhook.  Many thanks to WB3DDM for the idea.

Have a good weekend!

Aloha es 73 de KH6JRM--BK29jx15