Trap Vertical Antennas

Some operators will say that trap verticals aren't worth a 'plug nickel' as the saying goes. Yet others swear by them and attribute much of their success on the air to the trap vertical antenna in their antenna farm1.The long and short of it is that you either love a trap vertical or you hate them. many hams have erected commercial trap vertical antennas and came away from the experience with a bad taste in their mouth. In defense of the trap vertical antenna one would have to wonder how the antenna manufacturers stay in business if the antennas don't perform. How many time shave you heard an amateur radio operator sell (or give away) a trap vertical because "the $%#!& thing doesn't work"? And then the ham who received the trap vertical swears by it by naming contact after contact they made on the very same antenna. What does the success that one radio operator has with a trap vertical compared to the failure of another tell you? In a word - installation.

What is a 'trap vertical antenna'?

The traps (or coils) are inserted into an antenna to make it appear to be resonant quarter-wave antenna for each of the bands the trap vertical is designed for. Detractors to trap vertical will state that antenna power is lost in these trap sand therefore a trap vertical antenna should not be used.



Basic Antenna Assembly Notes

If there is one thing that trap vertical antennas do not like it is water. Water (especially around costal areas) leakage into the connection between trap antenna tubing will invariably lead to corrosion between them. Corrosion build up between the various elements of any antenna always contribute to the decline to the antenna efficiency. Once this corrosion spreads you trap vertical becomes a trap dummy load.

The best way to alleviate corrosion build up on any type of antenna is to prevent the water from entering your antenna connections. To begin with antenna parts that interconnect should be totally free of dirt, oil, film, or any other type of residue. Take a piece of fine steel wool, a ScotchBrite pad, or fine sandpaper and burnish both parts of the antenna where they will come into contact with each other. Once you have the antenna parts burnished you will want to wipe them down with ordinary rubbing alcohol to remove the fine dust left behind during the burnishing process. Don't shortcut the assembly process by wiping the antenna parts with dry rag or paper towel! The next step is a liberal application of Penetrox A, but don't overdo it and waste the pricey Penetrox A. Once this is done you can then assemble the parts and use whatever clamping mechanism the antenna manufacturer provides.

Once the two matching antenna parts are assembled you with need to prop them up where they are vertically oriented to prevent anything used in the next step from running off onto the ground. There are two methods you can use to seal a connection for trap verticals, liquid tape or spray paint. Some antenna builder use both the Liquid Tape and the spray paint. For the application of the Liquid Tape you only need enough on the supplied brush to form a gasket of sorts around the edge of the antenna tubing. If you opt to use spray paint you need to be sure to seal this area as well. Some antenna builder will use the tape and then spray over top of it with the paint. As with other parts of your trap vertical antenna project, don't scrimp on the paint! Use quality paints like Krylon® or RustOleum® clear to seal not only the joints but the entire antenna to help stave off corrosion. And there are some that paint their antennas various colors to blend in to the surroundings to help prevent nosy neighbors and homeowners associations from seeing them.

Trap Vertical Installation

Installing a trap vertical antenna can not, and should not, be something you do in a rush. If you are going to erect such an antenna then you should go about the task in a planed, organized manner. Consider the following steps BEFORE you get started with building your trap vertical:

  • Familiarize yourself with the instruction manual2.
  • Prepare the antenna mount and area where the antenna will be mounted.
  • Assemble all the needed tools for the assembly and installation.
  • Don't forget the Penetrox A, CoaxSeal, Liquid Tape, and filler grease.
  • Prepare and install the feedline from the shack to where the trap vertical will be mounted.
  • Prepare and install any recommended radials3.

You may well be the local antenna guru but even a guru has a methodology in place before, during, and after assembling and installing and antenna. This goes for any type of communications antenna, not just trap vertical ones.

Footnotes:

  1. An antenna farm is a reference to the antennas used at an amateur radio operator's location. It is generally believed this term stemmed from the habit of "planting" antennas in the back yard.
  2. While going through the manual be sure to also familiarize yourself with the various parts of the antenna.
  3. Radials under a vertical antenna are always a bone of contention for amateur radio operators. You should always follow the recommendations of the manufacturer. For a more in depth discussion of radials for your vertical antenna you might find this information helpful:
    1. The question is frequently asked, "should I mount my vertical on the ground, or get the base up in the air?" Getting the antenna up in the clear is always better than having it mounted at earth level and surrounded by rain gutters, house wiring, trees, power lines and so forth. However, getting the vertical antenna up in the air also means that radials, as many as possible, should be used. The average installation (if there is such a thing) usually consists of three or four radials (or more) cut for the lowest operating frequency. Such a system should give a good performance.
      By Lew McCoy, W1ICP
      QST September 1972, pp. 14-16, 28
      Reprinted with permission, September 1972 QST; copyright ARRL