Thursday, November 17, 2011

Simple Antennas for the Hawaii Amateur Radio operator, a continuing series

A loop approach to restrictive antenna conditions.

As I was reading the November 2011 "QST" today, I ran across an interesting antenna idea from Cristian Paun, WV6N.  His article entitled "An Antenna Idea for Antenna Restricted Communities" on page 35 really hit home.  My space restrictions are severe and the antennas I use certainly work (inverted "vees", vertical monopoles, and loops), but they could be better and perhaps even smaller.  Cristian describes a small loop he built and placed in his garden.  Previously, he had been using various mobile antennas between 3.5 and 30 MHz with some degree of success.  He wondered if he could use less space and yet produce results surpasing his best efforts.  Apparently, the small magnetic loop he designed and used proved most useful, with some improvement over the mobile antennas he once used.  Cristian's instructions are fairly simple and the final product is attractive, discrete, and almost sculture-like.  He concludes by saying "small or magnetic loops turn out to be a viable choice for those hams living in restricted areas.  Depending onthe efficiency of the loop, they can come close to the performance of a full size dipole at a height of 1/2 wavelength...They radiate well at low angles for DX contacts as well as at high angles for short skip communications."  I believe MFJ makes a magnetic loop and tuner for around $400.  MFJ also sells loop tuners that you can attach to a homemade loop that can be placed either outside or tacked to the ceiling of your "shack".  This could be another way to get on the air if you find no other way to erect an antenna.

My experience with loops.

I must admit that the only loop antennas I have had were of the one-wavelength variety strung under the qth or erected temporarily in a delta configuration in the back yard using a single 32-foot fiberglass mast.  A few months back I erected a temporary 20-meter delta loop near the garage and it performed well.  As I remember, I used 69-feet of #14 gauge housewire, with each side of the triangle running 23-feet.  I fed this homebrew skyhook at the lower left-hand corner with 450-ohm twin lead.  I ran the twin lead into a 4:1 balun.  Twenty feet of RG-6 ran from the balun to the trusty Drake MN-4 and then into the Swan 100-MX.  The system worked well until a strong rainstorm took the structure down.  I made a mistake in not guying the mast properly.  I may try this delta loop again, only this time I will take care to build the antenna better.

Mobile antennas can be used in a pinch.

I know several amateurs who use mobile antennas ranging from Hustler systems to the latest Tarheel antennas.  With a decent radial field or elevated counterpoise, these mobile antennas will get you contacts at a reasonable cost.  I have used old Hustler masts, loading coils, and whips to launch my signals from compromised antenna locations.  I had a lot of fun despite the obvious limitations of mobile antennas.  Other systems, such as the Budipole and Outbacker antennas, may give you a more costly alternative to getting on the air.  As for me, I prefer to "roll my own."  There is a certain satisfaction in building your own antenna and actually having the contraption work!  To that end, I have accumulated several antenna books and a well-stocked "junk" box for my antenna projects.  In this area, the local hardware store can be a real treasure chest of parts, wire, and tools for your next antenna project.  Half the fun of being on the air is designing and erecting your own creation.  Besides, when I am working on antennas, the xyl always knows where I am, in case the "honey-do" jar gets filled up.  Now that I am semi-retired, there is enough time to keep the house in repair and to pursue amateur radio on a more regular basis.

That just about wraps up this monologue.  Have an excellent weekend with many contacts.  You may even want to build your own antenna....go for it...have fun!.

Aloha es 73 de KH6JRM
Laupahoehoe, Hawaii (The Big Island).