By Peter Inskeep NO2D
Almost everyone is familiar with vertical antennas. Long, thin poles that reach skyward. They promise omni-directional reception and transmission. They take up very little space. They are ideal for small plots of land. However, they do have some downsides. If ground mounted they invariably require an extensive network of radials. The more, the merrier, they say. Sometimes buried and sometimes laid out on the surface with hopes that no one will trip on them or mow them down. Multi-band designs can get quite complicated. Another common complaint about verticals is that “they radiate equally poorly in every direction.” That last quote is direct from a sales person at a well known amateur radio retail dealer. Generally speaking, because of their low radiation angle they are not that good for close in work.
So, why bother with verticals? A good commercial built vertical can provide multi-band operation without the need for a tuner. A good commercial vertical can also be very expensive. Some commercial vertical companies claim that their verticals do not need radials. Take that with a grain of sand. Home brew verticals, on the other hand, can be built very inexpensively, especially if one wants to use it only on a single band. To get around the need for dozens of radials a vertical can be mounted above ground, when it will require only a few (4 will do) radials. Mounted above ground it is generally called a ground-plane vertical.
Taking the positives and the negatives into account I decided to build a home brew vertical to see how well it might work. Rather than go out and buy aluminum poles to act as the radiator, I decided to just use a piece of 14 gauge wire. My design frequency was 14.035 MHz. Think of a wire sixteen plus feet long. Pieces of wire that long usually don’t stay up in the air by themselves. How could I support this wire vertically?
Fortunately, there were some fiberglass poles in the garage left over from my defunct Lightning Bolt Quad, which bit the dust a few years ago in a violent wind storm. The quad had 16 fiberglass spreaders. Three of the spreader poles when fit together made a mast about 20 ½ feet long. By the standard formula (468 / Freq in MHz.) half wave dipole resonant at 14.035 MHz. should be 33.345 feet long. To determine the length of a quarter wave vertical, simply divide 33.345 by 2 to arrive at 16 feet and 8 inches, the appropriate length for the quarter wave antenna. The formula above is for a half wave dipole, so just divide it by 2.
Strip the 14 gauge wire and cut it to 16’ 8”, plus a few more inches. Tape one end to the top end of the fiberglass poles, ie., mast. Run the wire down the mast, taping it for support at various places. The bottom end of the wire was about 4 feet from the bottom of the mast. Tuck the bottom end of the radiator under a hose clamp to make it secure. Then attach another hose clamp to the mast about an inch under the upper hose clamp. Stick a short piece of 14 gauge wire through that hose clamp, making sure it does not touch the antenna radiator. This is used to connect the ground radials, and one side of the ladder line. Cut 4 radials from the same spool of 14 gauge wire. Strip any insulation that may be on the wires, as insulation can lower the resonant frequency. All should be the same length as the radiator, 16 feet and 8 inches, plus some surplus for tying them off to insulators. Solder one end of each radial to the short wire below the lower end of the radiator.
As this antenna is designed to be a ground-plane, it must be mounted above ground. It should be mounted high enough so that the radials do not inadvertently hit someone walking underneath them when extended. I chose to mount this 20 ½ foot long pole to the railing of my back deck. Since this was an experimental antenna I just used rope to tie it to the railing of the deck. (This step requires permission from the boss, which I managed to obtain.). I connected a feed line made of window line. It can be whatever length is necessary to reach from the antenna mast to the rig tuner. A tuner is required for this antenna. One side of the window line is soldered to the radiator stub at the upper clamp. The other end is soldered to the short wire that connected with the 4 radials at the lower clamp. At this point envision a long non-conductive pole with a wire running vertically from the top down to the feed line. Also imagine 4 radials spread out around the deck in roughly 4 directions so no one would run into them.
In my case the window line went in through a back basement door to the tuner in my shack. Getting window line into a house can be difficult. Some folks will terminate it with a 4:1 balun outside the house. Then they run coax from the balun in to the tuner. Either way, some ingenuity is required to get the feed line into the shack and to the tuner.
A properly constructed vertical antenna can be fed directly with 50 ohm coaxial cable. Almost all are, commercial or otherwise. They should work on their design frequency. They won’t work well, or at all, on other bands, unless they are designed as multi-band verticals. Using window line (or ladder line if you have the patience and skill to build it), on the other hand, allows the antenna to be used on other bands than the one for which it was designed.
One of my tuners is an LDG AT100 ProII. The window line terminates in a small 4:1 balun, which is then connected to the LDG tuner with a short piece of coax. Using this setup, it tunes very easily to 1.0:1 on the bottom end of the 20 meter band. It also tunes to 1.0:1 on both 17 and 15 meters. 12 meters is not so good, at 1.7:1. 10 meters does great at 1.0:1. Would you believe that it also tunes on 30 meters? Actually, it does get down to 1.3:1 SWR on 10.115 Mhz. It even tunes down to 1.0:1 on 40 meters. I doubt that it does very well on that band, though, so I seldom use it there.
On 20 meters it often equals, or out performs, my doublet up at 30 feet, or my dipole, also at 30 feet. Sometimes it is better, and sometime not. On the other bands the story is more mixed. It occasionally works better, but more often than not the doublet, tuned through the same LDG auto-tuner, will outperform it.
It might be an ideal inexpensive antenna for someone who wants to operate several bands but does not have the room or physical supports for a long wire antenna. It gives me another weapon, especially when I am searching for DX. They say that the main strength of a vertical is its low angle of radiation, which is good for hunting DX. A dipole or doublet, on the other hand, especially at a low height of 30 feet, does not really have a very good low angle of radiation, and may not be as effective as a vertical for DX.
Figure 1 shows an overall view of the vertical attached to the corner of the deck. The radials are difficult to see, but stretch out, generally speaking, from the mast just at the height of the deck rail, well above head level. Spread the radials out as equally as you can.
Figure 2 shows how the window feed line is attached to the mast. Note that the end of the radiator, coming down the pole, goes under the hose clamp and then directly to one end of the feed line. The other end of the feed line goes to the short 14 gauge wire that is under the lower hose clamp. There is no connection between the upper hose clamp or the radiator, and the lower hose clamp, which serves to secure the 4 radials as well as the other side of the window line.
This is not a difficult antenna to build if one can find a suitable mast. Crappie fishing poles are said to be effective for this purpose. If you have or can get a 17 foot long piece of aluminum or copper, by all means use that instead of the wire. It should work even better.
The two keys are first, design it as a ground plane vertical to avoid having to lay out dozens of radials. Second, use window line, or build your own ladder line so that it can be a multi-band antenna. My best DX with this antenna so far? South Cook Islands, Croatia, Germany, Belgium, and Chile. All with 5 watts or less. In some cases my dipoles or doublet will outperform the vertical. In other cases, the vertical wins. Nice to have all three to choose from.