Chassis or Radials when stationary?

Posted on 4th Jan 2023

When operating from your vehicle in a stationary capacity using a car as an electrical ground for a vertical antenna is not recommended, as generally it is not a suitable or efficient electrical ground for the antenna. Radials are a better option for several reasons:

Consistent Ground: Radials provide a consistent electrical ground for the antenna, whereas the electrical properties of a car's chassis can vary significantly depending on its make and model. This can lead to inconsistent performance and weak signals.

Reduced Interference: Radials are installed either at a height above the ground or in contact with the ground, reducing the amount of interference from the ground and increasing the performance of the antenna. In contrast, a car's chassis is generally floating above ground at a non optimal height, leading to increased interference and reduced performance.

Optimal Length: The length of the radials can be optimized for the frequency being used, whereas the length of a car's chassis is fixed and cannot be adjusted to match the desired frequency.

Durability: Radials are typically made from materials such as copper or aluminum, which are durable and can withstand the elements, whereas a car's chassis can be affected by factors such as rust, corrosion, and weather conditions.

Whether elevated radials or radials on the ground are better depends on the specific application and the desired outcome. Both options have their own advantages and disadvantages:

Elevated Radials: Elevated radials are radials that are installed above the ground, rather than being attached directly to the ground. The main advantage of elevated radials is that they can help to improve the performance of the antenna by increasing its height above the ground and reducing the amount of interference from the ground. Additionally, elevated radials are often easier to install, as they do not need to be buried in the ground.

Ground Radials: Ground radials are radials that are attached directly to the ground. The main advantage of ground radials is that they provide a more stable and consistent electrical ground for the antenna, as they are in direct contact with the ground. Additionally, ground radials are often easier to install, as they do not need to be elevated and can simply be attached to the ground.

In general, it is recommended to use a combination of both elevated and ground radials for the best performance. The elevated radials can help to reduce interference from the ground, while the ground radials provide a stable and consistent electrical ground for the antenna.

So, the choice between elevated radials and ground radials depends on the specific application and desired outcome. Both options have their own advantages and disadvantages, and a combination of both is often recommended for the best performance.

Moving along, the radiation resistance of a vertical antenna is also affected by the use of radials in several ways.

Improved Ground: The use of radials helps to improve the electrical ground for the antenna, reducing the amount of current that flows into the ground and increasing the amount of current that is radiated into the air. This helps to improve the efficiency of the antenna and increase its radiation resistance.

Increased Height: Elevated radials help to increase the height of the antenna above the ground, reducing the amount of interference from the ground and improving the performance of the antenna. This can also increase the radiation resistance of the antenna.

Improved Impedance Match: The use of radials helps to improve the impedance match between the antenna and the transmission line, reducing the amount of reflected power and increasing the efficiency of the antenna. This can also increase the radiation resistance of the antenna.

Increased Signal Strength: The use of radials helps to increase the signal strength of the antenna, as the radials provide a stable and efficient electrical ground for the antenna, reducing the amount of interference from the ground and increasing the performance of the antenna. This can also increase the radiation resistance of the antenna.

Therefore the use of radials can have a significant impact on the radiation resistance of a vertical antenna. By improving the electrical ground, increasing the height of the antenna, improving the impedance match, and increasing the signal strength, radials can help to increase the radiation resistance of the antenna and improve its overall performance.

In many cases this is the underlying reason you see your SWR increase with the addition of radials. You are changing the feed point impedance by the change in radiation resistance of the antenna system. The radials provide a lower loss path for the reflected power to be re-reflected via teh radiator or transmission line forward and back until it is radiated or lost as heat. 

In conclusion, radials either elevated or ground mounted are a better option for a vertical antenna's electrical ground compared to a car's chassis. They provide a consistent and efficient electrical ground, reduce interference from the ground, can be optimized for the desired frequency, and are durable. 

_{Curtis Turner - KB3CMT}