Ground radials: Electrical difference between 14 gauge and 18 gauge? Lifespan difference?

Question

I am starting the process of installing a vertical ant (6BTV) and radial ground system. I am ready to buy the wire.

I would like to know if there is an electrical difference between 14 gauge and 18 gauge wire when used as a radial ground system?

I would also like to know how long the 18g will last compared to the 14g?

For instance, can the 18g wire be reasonable expected to last ten to fifteen, or even twenty, years while laying on the dirt with grass growing over it?

How long might 14g wire be expected to last?

Thank you for your time.

Answer 1

Larger wire will have less resistance. However, the resistance of the radials in either case is negligible compared to the soil resistance, so I wouldn't worry about it.

Longevity would be my concern. Commercial broadcast towers use 10 gauge bare wire. Anecdotally, there are plenty of amateurs happily using 18 gauge wire.

Corrosion depends on many factors. Corrosion rates could be anywhere from 0.0002 to 0.15 mm/year, depending on soil conditions. Solid wire will last longer than stranded, due to decreased exposed surface area.

18 gauge wire has a radius of 0.51mm. Most soils won't be especially aggressive. At a rate of 0.0002 mm per year, it takes approximately 2500 years to corrode all the way through. So assuming favorable soil conditions, you'll be dead long before the wire rots away.

I think the bigger concern is mechanical strength. Digging animals can chew through wire or push it up. Frost heave and thermal expansion/contraction can cause the wire to pop up where it's subject to snags by foot traffic or mowers. Digging to plant a tree, etc. could cut a wire with a shovel. I'd expect to lose more radials this way than by corrosion. In my freezing, mole-infested location I bury the radials to anchor them more securely.

For the amateur, repairs are cheap and easy. So economically it makes little sense to spend a lot of money on robust wire. If 18 gauge wire hits the price point you need to install enough radials to have an efficient antenna, I'd say go for it.

Answer 2

The longevity of your radials will depend on many factors:

• Wire material: copper, aluminum, steel
• Wire coating: bare, enamel, vinyl, galvanized
• Environment, e.g., acidity of rainfall, soil, etc.
• Common connection means: bolted, twisted, soldered, etc.

The effectiveness of your radial "field" will depend on soil losses and coverage of the area in which your signal's electromagnetic waves are produced. The nature of your radial implementation will depend on how much time and treasure you want to invest, "treasure" comprising real estate as well as hardware. It's also important to separate efficiency from your need/desire to have the radials produce resonance at the antenna's feedpoint.

My QTH suffers from perhaps the poorest soil conductivity in the US, according the the map in Reference Data for Radio Engineers. Add to that the deleterious effects of acid rain resulting from power plants in the midwest and you have a very difficult situation.

W8WWV published an article in Ham Radio magazine many years ago which described a very cost-effective scheme which has served me well for over a decade: lay lengths of 4-ft wide galvanized steel fence to form a screen on the ground. Greg's analysis concluded that returns diminish rapidly for more then eight (8) such "radials" and when the length of each "radial" exceeds the height of the vertical radiator.

Of course, each "radial" delivers substantial screening of the lossy ground. As an added bonus, these "radials" are easily rolled up if necessary, but they also "disappear" fairly quickly into the grass if you want to mow over them.