Friday, March 9, 2012

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

Thanks to the recent CME and flares from the sun, my operating time was brief today.  Everyband was noisy and all I did was listen to a few strong signals on 20-meters.  I made a few calls, but with only 10 watts to the vertical dipole, I didn't work many people.  So, I spent the day cleaning and tightening my loop, 20- meter vertical dipole, and the inverted vee in the backyard.  When I finished with basic maintenance, I was once again on the prowl for interesting, homebrew antennas that even I could build.  One of my favorite antenna books is "Simple and Fun Antennas for Hams" published by the ARRL.  The book is loaded with real-world, practical antennas you can build yourself with a minimum of cost and time. 

I came across an interesting antenna that may appeal to those of us restricted by space and CC&Rs. Jeff Brone, WB2JNA, adapted a design by Robert Johns, W3JIP, which appeared in the August 1998 issue of "QST".  Jeff's article is found in chapter 12, pp. 7-8.  Basically, Jeff's project is a "Cheap and Dirty Multiband Antenna" using an end-loaded wire (with a coil) balanced by a counterpoise.  There are several commercial variations on this theme by MFJ and B & W.  Since the antenna is so simple to build, you may want to forego the commercial versions and "roll your own."  According to Jeff, all you need are 32 feet of #14 to #18 copper wire, with 20 feet bare in order for winding the loading coil; two  "dog-bone" end insulators; an empty two-liter soda bottle; two alligator clips; 32 feet of insulated wire, such as #16 or #18 speaker wire for the counterpoise; and coax to connect your rig to the antenna.

Measure and cut off around 13 feet of wire.  This will give you enough for a span of about 12 feet after you have secured each end of the wire to its insulators.  Wrap about 17 to 20 turns of bare wire on the soda bottle to make your coil.  Having done this a few times, I can say this is the hardest part of the project.  Be sure you leave enouogh space between the turns so that there is sufficient room for an alligator clip to fit without shorting to adjacent turns.  You can use tape, coil dope, silicone seal or whatever you like to hold the coils in place.  Take a length of coax (I happened to have some RG-6 with adaptors on hand) and solder an alligator clip to the center wire.  The length of the counterpoise attached to the shield of the coax will depend on the lowest band you intend to use.  Like Jeff, I used 32 feet for 40 meters.  Connect the center conductor's alligator clip to the coil, about 13 turns from the main radiating wire.  Run the 32 feet of counterpoise along the floor of your room or apartment.  Be sure to keep the end away from people and pets, because there is a large amount of rf at the end, even for QRP operations.  Connect the other end of the coax to your rig and transmit.  You may have to try different turns to get a good SWR.  To use the antenna on 20 meters, connect the alligator clip about 2 to 3 furns from the front of the coil.

You may want to cut the counterpoise about 16 feet in length and attach an alligator clip to its end for attaching the other 16 feet when you want to work 40 meters.  The antenna cost me nothing, since I had an empty diet Coke bottle, some insulators in the junk box, and about 100-feet of #18 speaker wire in the garage.  I was surprised how well this homebrew antenna worked.  You could even mount this on a wall of your operating position if you ran QRP levels of 10 watts or less.  This antenna will not perform like a beam or even a decent dipole in your yard, but it will get you on the air.  Of course, your success will vary--that's part of the fun of Amateur Radio.  Besides, if this antenna does work for you, you have saved some money and built something you can call your own.

Have a good weekend!

Aloha es 73 de KH6JRM--Laupahoehoe, Hawaii, BK29jx15.