Don’s Antenna talks by N4DJ

  The above chart gives the approximate radiation angle needed for various distances. I noted in blue and in red the range best covered by horizontal antennas 1/2 and 3/8 wave high. All antennas will have a range of elevation angles centered on the theoretical peak radiation angle determined by the distance above the ground. The extremes of this range are called the 3 dB points. Signal strengths at these extremes are not significantly weaker than at the peak or middle of the range. 3 dB is not very much difference. It is only about 1/2 of a standard S-unit. As you move farther off the peak the signal decreases more. Usually the rate of decrease gets faster and becomes more significant until a null is approached where there is usually a rather significant dip in signal strength. Depending on the height above ground this dip can be rather dramatic. The higher the antenna the sharper the nulls. Antennas that are close to the ground tend to not have significant nulls. A low 40 meter or...