Simple and Effective All-Band Antenna

In 1963, I was lucky enough to attend a presentation on antennas, given by Lew McCoy, W1ICP (SK). He introduced me to an antenna which I immediately built and have used whenever it has made sense to use, for almost 50 years now.

 

Interesting enough. L.B. Cebik, W4RNL (SK) also wrote an interesting article entitled "If I could only have one antenna".  He chose the same antenna.  (Although I like this antenna, I would have chosen the LAZY LOOP instead.).

 

What is it?

 

An 80m Dipole, fed in the center with openwire feedline.

Somtimes called a Double-Zepp Antenna.

 

HOW LONG SHOULD THE FEEDLINE BE ?

 

In on the air (or on the net) discussions, you often hear people speaking of the optimum feedline length.  There is only one useful answer to this, and it was put forth by Lew in his presentation:

 

 "The feedline must be long enough to reach from the feedpoint of the antenna to the connection of the matchbox in the shack."

 

The reality is, you use this length but sometimes have to add a little extra feedline to avoid certain problem lengths.  More on this, later.

 

VARIATIONS OF THIS ANTENNA:

 

Over the years I have used this antenna in various forms at 50+ different QTHs.  I played a bit with the lengths of the legs and made some interesting (gut feeling) discoveries:

 

Leg Lengths       Difference                                                                   

   2x 20m            My stake-in-the ground starting point

   2x 17m            No dicernable difference

   2x 13m            Almost no dicernable difference

   2x 10m            Not quite as good but still very effective on all bands

 

FOR SMALL BACK YARDS, try building this antenna half size.  You will be surprised to see how well it still works on all bands except 80m.  It will still work on 80m, but the effeciency will begin to drop off as the antenna gets smaller than 26m overall length.

 

INVERTED-Vee VERSION:

 

To save even more space, erect this antenna as an inverted-vee antenna.  For instance, an inverted-vee with 2x 8.5m legs (28' legs) requires only about 16m (50') of horizontal space, yet it is an outstanding performer on 40 through 10m and will still load and work on 80m.  Using x2 6.5m legs, it fits in an even smaller space.

 

HOW HIGH SHOULD IT BE?

 

As high as possible, which for most people is typically 10 to 15m (30 to 50 ft.).  Even if it is as low as 10 ft. (ca. 3m), it will still work, but you won't be breaking many DX pileups at that height.

 

WHAT SHOULD I USE FOR A POLE (MAST)?

 

The best thing to use is a non-metalic pole.  You can use wood, but a 10m (33') wooden mast is pretty heavy.  You are much better off using a heavy duty telescoping fiberglass pole such as the 12m (40') pole sold by Spiderbeam.  See: http://www.spiderbeam.com/gate.html 

 

HOW SHOULD YOU MATCH IT TO 50 OHMS?

 

With a matchbox, and of course as good of a matchbox as possible. There are lots of different kinds of matchboxes on the market, deploying several different kinds of technology.

 

MY LIST OF "GOOD" SYMMETRICAL MATCHBOX TECHNOLOGIES:

  1. LINK COUPLED MATCHBOX
  2. Double-L Symmetrical Matchbox
  3. Double-T Symmetrical Matchbox
  4. Asymmetrical Matchbox (floating) with Balun on the TX side
  5. Asymmetrical Matchbox with Balun on the Antenna side

Whenever using a balun, I strongly recommend using an EXTERNAL BALUN, rather than the built-in matchbox in the rig.

It should also be a current balun, NOT a voltage balun.

In fact it should be a 1:1 balun, NOT a 4:1 balun as most people use.

 

REASON?  See: http://www.karinya.net/g3txq/tuner_balun/

 

More Info on Baluns:  HERE

 

NOTE: My priority list above applies only to matching SYMMETRICAL antennas fed with openwire.  

For other antenna types, the order will change.

 

SOME PEOPLE SAY THIS WORKS BEST, OTHERS SAY THAT WORKS BEST ???

 

Well they are probably all correct.  They found something which worked very good for them.  

 

MOST PEOPLE have never tried all of the solutions listed above.      

I HAVE.  

Here are some simple guidelines:

  • For QRP, anything works.
  • For 100w, almost anything works.
  • For 1000+w, it can get real dangerous trying to find a solution which does not burn your lips each time they touch the mic, or burn your fingers each time they touch the metal of the key. You will get the best results if you use a symmetrical matchbox, rather than an asymettrical matchbox with a balun.

Interresting, I got different results in different situations.  So even if two people appeared to try the same method, they may very well have experienced different results.  Part of the reason of course, is that they are not really the same.  Perhaps the feedline length is different, etc.

 

EINSTEIN WAS NOT COMPLETELY CORRECT:  Sometimes you do get different results when you try something again, especially if the second try is at a different QTH.  ALWAYS expect the possibility of different results!

 

 

SPARKS!  MY MATCHBOX ARCS!

 

What do you  do when your matchbox arcs and sparks on one or more bands?

 

There are two answers here,

  • one for PORTABLE installations
  • one for PERMINANT installations.

 

FIRST: Before you do anything to the antenna, be sure your matchbox is designed to handle the power level you are working with.  If it is, then proceed as described below.

 

For PORTABLE installations, it depends on how much I really even need that band. Sometimes the best thing to do is just not work that band.  If it is a contest QTH and 40m arcs or sparks inside my matchbox, I have to address the problem.

  1. First, I reduce the output power of my transmitter.  I have often seen where my matchbox would arc at 100w but run perfectly well without arcing if I reduced the output power (for just that one band) to 80 watts.
  2. If that does not work, or it is not an acceptable solution, adjust the feedline as described under PERMINANT installations below.

 

For PERMINANT installations, I want my antenna to work with full power on all bands.  After all, that's part of the reason I chose "this" antenna.  It is supposed to be an ALL BAND antenna.

  • The length of the feedline should be changed by approximately 1/8 wavelength on the band that is incurring problems.  Since it is probably not possible to shorten the feedline and still reach the shack, we need to lengthen the feedline.  The 1/8 wavelength is a "ballpark" number and not critical.
  • Example: 40m is arcing.  1/8 wavelength on 40m is approximately 5m long.  Don't forget to apply the Velocity Factor.  The VF for openwire feedline is usually about 0.9.   The length of additional feedline needed is: 0.9 * 5m = 4.5m. This is about 15 ft.
  • Add about 13 to 17 feet more feedline to your existing feedline.  You may add this inside of the shack or outside of the shack.  If you add it outside the shack, be sure to weather-proof the connections.
  • After adding the feedline, check the SWR on ALL bands.  Sometimes changing the feedline length fixes one band but causes problems on another.
  • With a little bit of trial and error, you will always find a length which works on all bands without arcing inside of your matchbox.