Thursday, August 28, 2014

Simple Ham Radio Antennas: Antenna Basics. Post #291

One of the joys of being semi-retired, is the ability to attend a few more face-to-face meetings with your amateur radio friends.  Such was the case today, Thursday, 28 August 2014.

My xyl had a substitute teaching assignment today, while I didn't.  That gave me some time to go shopping, do the laundry, take care of a few commercials for this weekend's Labor Day Drag Races (I'm the tower announcer and report back to several Hilo radio stations with race results), and meet up with a few ham friends who gather daily at the Hilo Jack In The Box Restaurant.

The meetings are quite informal, with most of the discussion centered around antennas, homebrew projects, and various communications issues.  Despite having 37 years of amateur radio experience "under my belt," I always find something new and interesting at these meetings.

One of the things that has always bothered me is the amount of misunderstanding surrounding antennas, both homebrewed and commercial.  It's hard to sift out the claims and get to the basic "truths" of antenna design, building, testing, and use.  When I raised this question, Dean (KH6B) gave me several reprints of antenna articles from the past which helped clarify my thinking.  Both Dean and I have extensive backgrounds in commercial broadcasting--Dean comes from the broadcast engineering realm of radio, while I stumbled in from the programming and news departments. Dean has built and maintained several AM and FM stations and has served as a consulting engineer on numerous radio projects on the U.S. mainland, Hawaii, and throughout the Pacific Rim.  He has a tremendous collection of reference material dealing with antennas, which he freely shares with those of us attending the informal meetings over coffee and breakfast.

Among the antenna articles I received today was an essay entitled: "Antennas--Some Rules of Thumb for Beginners" by James R. Duffy (KK6MC/5).  The original article can be found here:  http://www.norcalqrp.com/features/bgnsant.html, dated 31 January 2004.

James lists 13 basic antenna concepts that will help you build efficient wire antennas that deliver outstanding performance at a minimal cost.

Here is a brief summary of those ideas:

1.  Any antenna is better than no antenna.  Rather than agonizing over an antenna choice, just put one up and operate. After operating with it for a while, you will become aware of your operating habits and the shortcomings of the antenna you have erected.  That will give you some hints as to which direction you should go with another antenna.  Building your own wire antennas is fun, educational, and fairly cheap.

2.  Higher antennas generally out perform lower antennas.

3.  Most people will be happier with a low dipole than a vertical.  Verticals require a bit more attention to work effectively and beginners can become frustrated in dealing with ground issues.

4.  It pretty much doesn't matter what kind of copper wire you use in an antenna.  The familiar formula for cutting a simple half wave dipole, 468/frequency (in MHz), will give you an approximate starting point for measuring out your antenna elements.

5.Whatever antenna you chose, if it is fed with coaxial cable, you should use a choke balun.  This will prevent the feedline from becoming part of the antenna which can cause all sorts of problems.  Various balun designs are discussed in the ARRL Handbook and in the ARRL Antenna Book.

6.  Buy one of these books and study it well. Antennas don't change much, so even an old copy of the Antenna Book will be very useful.

7.  Outdoor antennas perform better than indoor ones.  A thin wire supported an inch or more away from the building will be much better than one inside.  If you can dangle a wire out a second story window, feed it against a counterpoise wire.  The counterpoise is the "missing half" of your dipole.  You can string the counterpoise around your radio room, being careful not to touch the end of the wire during transmissions.

8.  Don't scrimp on feedline.  Good, low-cost feedline doesn't cost much more than the antenna it is feeding.

9.  Most single band antennas can be made into multiband antennas by feeding them with a balanced feeder like window line and using a tuner/balun combination to keep your rig happy.  This applies to loops as well as dipoles.

10.  If you have antenna restrictions, consider a temporary antenna.  The SD-20 Blackwidow Crappie Fishing Pole can be erected with a wire of choice to make a vertical in a matter of a few seconds.  With a few radials or a chain link fence as a ground, this can give a good account of itself.  If somebody complains about it, take it down and next time erect it where they can't see it.  

11.  Consider your operating practices in choosing an antenna.  If you can only operate in the evening, then even a high 10 meter antenna will not provide you with much operating time.  The band will usually be dead after sunset.  On the other hand, a 40 meter dipole will provide you with a number of contacts late into most evenings.  It can also be used on 15 meters for those occasions when you can operate during the day.

12.  Avoid the temptation to "have it all."  Multiband antennas are often attractive to new comers.  So are electrically "small antennas."  They are by necessity compromises, and usually don't work as well as single band antennas.  I suggest erecting a single band dipole and using it for a while.  As you get used to operating or have desires to try out other bands, you can erect another antenna, or feed the one you have with ladder line for muliband use.  You can build and feed a lot of single band dipoles for the price of a R-7000.  That antenna, by the way, is an excellent performer if you have the necessary money for it.

13.  Homemade antennas are often better and far cheaper than commercially built antennas.  Building wire antennas is educational, fun, and cost effective.

I hope someone finds this useful.  See you on the air--Dr. Megacycle KK6MC/5.

Comment:

During my almost four decades of being an amateur radio operator, I've found the above listed advice and hints true in most cases.  Simplicity, good design, and careful craftsmanship will spell success in the antenna game.  The "Rules of Thumb for Beginners" are technically and economically sound.  Simplicity, stealth, and low power will enable you to stay on the air with a minimum of hassle from your community.

Source:

Duffy, James R. (KK6MC/5).  Antennas:  Some Rules of Thumb for Beginners.  (http://www.norcalqrp.com/features/bgnsant.html.

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Until next time,

73 de Russ (KH6JRM).
Site Administrator.