Last week, an online amateur radio retailer contacted me about writing some blog posts for his website. One of the topics he suggested was “Choosing an HF vertical.” Here’s what I wrote this morning:
Choosing an HF vertical
For many amateur radio operators, a vertical antenna may be the only option they have to put up an HF antenna. They may, perhaps, live on a small lot, or they may not have suitable trees or other antenna supports from which they can hang dipoles.
Fortunately, there are many good products on the market. Unfortunately, there is some confusion about the different types of verticals out there. This short article will attempt to give you some guidance on how to choose the right vertical for you.
Trap verticals have been around for a very long time. My very first HF antenna back in 1971 was a hy-gain 14AVQ. These verticals use “traps” that are parallel resonant circuits to electrically isolate portions of the antenna when transmitting on various bands. The traps make the antenna act as if it were a resonant quarter-wave vertical. For example, when the 14AVQ is being used on the 10m band only the lower portion of the antenna is active. When operating 40m, the entire length of the antenna is active.
Trap verticals need radials to operate effectively, and the more the merrier. Take this into consideration, when deciding whether or not to purchase a trap vertical.
In recent years, several manufacturers have introduced vertical antennas that do not need radials. GAP Antennas is one manufacturer that offers these kinds of antennas.
The manufacturers claim that these antennas are more efficient than trap verticals, and many amateurs use them with good results. There are some drawbacks, however. They can be difficult to tune, and they do require mounting at some distance above ground. The reason for this is that they are, in effect, vertical dipoles and if the end of the antenna is too close to ground, capacitive coupling will detune the antenna.
Non-resonant vertical antennas
A third class of vertical antenna that is becoming popular is the non-resonant vertical antenna. An example of this type of antenna is the LDG S9v43 Vertical Antenna, although several other manufacturers also make this type of antenna.
One reason that this type of vertical antenna is becoming popular is that it can be used across a wide frequency range. The resonant frequency of this antenna is actually about 5.4 MHz. With an antenna tuner, however, you can use the antenna on all bands from 80m to 6m.
This tuner can be located in your shack, but for the lowest loss, you will want to locate the tuner near the base of your antenna. Don’t try using it with the internal tuner in your rig. On some frequencies, the antenna impedance will be quite high, and most internal rig auto tuners do not have adequate range to provide a 50-ohm match.
These antennas require radials. There is no formula to calculating the length of the radials, but they should be at least 0.2 wavelength at the lowest frequency that you wish to operate.
We carry the entire line of LDG vertical antennas. The LDG S9v43 antenna is 43 ft. high and covers 80m – 6m, the LDG S9v31 antenna is 31 ft. high and covers 40m – 6m, and the LDG S9v18 antenna is 18 ft. high and covers 20m – 6m. All of these antennas use heavy-duty, telescoping fiberglass sections. The antenna is self-supporting, and because it’s very light weight, easy to install.
I know it’s not a comprehensive guide to how to choose an antenna, but that’s not the intent. I also know that it’s a bit slanted towards the non-resonant vertical, but that’s the kind of antenna that the company carries. Having said that, I’d love to hear your comments.