Tuesday, June 22, 2010

I’m about to install a homebrew vertical antenna ...

Q I’m about to install a homebrew vertical antenna and a system of buried wire radials. My only question concerns the radials. What sort of wire should I use? I would imagine that some wires would corrode in soil faster than others.

Divining an answer to this question is trickier than it seems. Being more of a general practitioner, the Doctor opted to consult with three prominent antenna specialists: Dean Straw, N6BV, Roy Lewallen, W7EL, and Tom Rauch, W8JI. The following answer summarizes their comments.

A Noninsulated copper wire can be expected to last several years in just about any kind of soil. Insulated copper wire is even better. Copper-clad steel wire should be avoided, however, because it has a relatively short life. And stay away from aluminum wire; it will turn to powder in a year or less!

The problem isn’t just the pH of the soil, but what the radial eventually connects to via the shield at the station end. It’s quite easy, even in what appears to be “favorable soil,” to have an electric potential that erodes the radials since there is a complex dc path that involves everything connected to the radial system. The only safe solution is to use copper wire—#16 or larger—bare or otherwise. Some bare copper radial systems buried at broadcast sites in the 20s have been uncovered and found to be virtually perfect! It’s hard to go wrong with copper.

From QST March 1999