Elevation angles

 

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 80 meter dipole can appear to be almost omnidirectional where a 10 meter dipole at the same height in feet can have very sharp nulls. Remember it is the height of the antenna in wavelengths that matters. An antenna that is 1/4 wavelength high on 40 meters is 1/2 wave high on 20 meters and 1 full wavelength high on 10 meters. Even low antennas can still have significant radiation at lower angles under the right conditions. One antenna with a lower peak radiation angle may not radiate as much at that peak as another antenna ( with a higher peak radiation angle) does at that same angle. One good example is a vertical is known to have a low elevation angle but a not so high dipole with a higher peak radiation angle might (and usually does) actually out perform the vertical.                              






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