How Many Radials Do I Need?

OK, so you don't have enough wire to lay down 120 - 1/4 wave length radials for your ground mounted vertical antenna.  They saying is more short radials is better than a few  longs ones.  But what is the ideal number of radials for the amount of wire you have? 

For the long answer, see the Aug 2003 issue of QST, page 39.

The Cliff Notes version is this formula:

N = 2.25(sf)^.25 L^.5

Where N is the number of radials for a given length of wire which will provide the minimum ground loss.

s = soil conductivity.  I used s=0.0045 for average soil in my computations.

f = frequency.  Use the frequency of the lowest band you will use on your vertical antenna.

L = the length of wire you have to use for radials.

If you have 1000 feet of wire, the optimum number radials for the following bands would be:

160 meters - 22 radials, 80m - 26 radials, 40m - 30 radials, 20m - 36 radials, 15m - 40 radials.

For 500 feet of wire:  80m - N=18, 40m - 21, 20m - 25, 15m - 28, 10m - 30 radials.

For the low bands more would be better.  3000 feet would be 38 radials for 160m and 45 for 80m.

73

Dave
W4DFR