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The SGC Smartuner gets energy into an antenna, but the design of an antenna is what controls what happens to the RF energy from there. For some antennas, the antenna is simply not complete without a radial system, or at least a counterpoise. Other types of antennas need no RF ground system at all. Most reference books on antennas provide solid guidance on radials and counterpoises, but only for antennas cut to a specific frequency. When using an SGC Smartuner, the rules have to change because the Smartuner operates across the full range of HF frequencies.
Radials and Counterpoises have two basic purposes:
1. To improve the RF ground conductivity for the ground current return path. Unless you live in a salt-water swamp, your ground conductivity makes a very poor path for the return of ground currents. This increases the ground losses and reduces the efficiency of an antenna that needs a good RF ground.
2. To provide a counterbalance for the feed point of the antenna to reduce RF radiation back to the radio room. The Smartuner changes the rules because there is no single frequency that you will be operating on, so all of the thumb rules for 1⁄4 and 1⁄2 wavelength radials don’t apply. It is possible to be either a purist or a pragmatist in deciding what radials to put in place. We’re going to be pragmatic about it and say, “Here are the thumb rules that work with a Smartuner":
A. If the antenna is balanced, you don’t need an RF Ground. Dipoles and Loops are the most common forms of balanced antennas in use. With a properly installed antenna fed by a Smartuner at the feed point, no RF ground is necessary.
B. If the antenna is unbalanced, a radial system or counterpoise is necessary for operation. The radial our counterpoise system is connected to the Smartuner RF Ground.
C. Base fed vertical antennas must have a good RF Ground system for efficiency. Vertical antennas can have radials mounted on or below the surface of the actual ground. If the radial system is mounted above the ground, it is technically a counterpoise and takes the place of the actual ground. An equally good ground can be created by mounting well-bonded chicken wire or other grid material to form the ground plane near the antenna.
D. Vertical antennas mounted high in the air will need to have a radial system mounted just below the antenna (a ground plane antenna) and connected directly to the Smartuner RF Ground. The ground plane on the antenna will shield anything mounted below it from RF, so a good place to mount the Smartuner for a raised vertical antenna is below the ground plane.
E. More radial wires are generally better. As the number gets larger, they improve the RF Ground less and less, to the point where there is no difference when adding one more radial to a system that already has 120 installed. Minimum systems of as few as 4 wires can provide an acceptable ground and increase the antenna’s efficiency by a significant amount. Generally, 6-8 radials is the minimum that should be used.
F. Radial wires should be as long as the antenna wire if possible. If you must use shorter wires, keep them as long as possible and use extra radial wires.
G. Antennas that use a vertical section as part of the radiator, such as the Inverted-L antenna, need to have a ground radial system just like a vertical antenna.
H. Horizontal, unbalanced antennas, such as a long wire or random wire, need an RF Ground wire that should be 10-15% longer than the antenna wire itself. This is often called a counterpoise. The RF ground wire in this case can be laid out in many ways, just so long as it does not cross over itself to form a loop. Indoors, such wires are often run under carpets or along walls, out of windows, or anywhere else convenient. This wire will often have large RF voltages on it, so it should be kept away from people or insulated to prevent contact.
I. Avoid connecting to a polluted ground. Building or Plant grounds can have a lot of other energy flowing through them that can get into your very sensitive receiver. RF Noise can come from many sources, particularly in industrial areas, and it can be present within the ground. Avoiding this energy is one of the main reasons for creating your own ground system.
While the Smartuner will provide a good match with a poor RF ground system and you will be able to transmit, your antenna efficiency will be low and you will be subject to RF problems that can make operation miserable at the very least. Getting the greatest efficiency out of your antenna system needs a proper RF ground unless you’re using a balanced antenna system. SGC’s book "HF User’s Guide", has an overview of the issues related to HF installation and operation and includes a section on antennas. You can download a free copy in PDF format from our Manuals Repo page.
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Published on: 2024-11-03 (15 reads)