More about antenna height and distance for Horizontal Antennas

 We know several things that help us relate antenna height to distance best covered by that antenna. We will limit this to one hop F layer skip. This is a primary path for most cases.

The height of the antenna determines the peak radiation angle. In most cases the radiation falls off about 3 dB when you go 15 degrees above and below that peak angle.  So we have an optimal range of 30 degrees where our signal is at its best. 

We also know that the F layer of the ionosphere exists somewhere between 150 to 250 miles high. So we have a range of heights as well as a range of angles. 

Consequently we can be pretty confident in the following:

Since an antenna 1/4 wave high has a peak radiation angle at about 90 degrees or straight up, it will be best for zero miles out to about 300 miles.

Since an antenna 3/8 waves high has a peak angle of about 55 degrees, it will be best from 125 miles out to 560 miles.

Since an antenna 1/2 wave high has a peak angle of about 30 degrees, it will be best from slightly less than 500 miles out to about 1250 miles.

Note that I said best signal. What that means is if the signal is maximum at the center of one of these angle ranges, it will be down only 3 dB at either end of the range. As distances get closer (or farther away)  the signal will become weaker and weaker. The optimal range is between the two angles where the signal is maybe 1/2 S-unit or 3 dB weaker. 3 dB is barely noticeable whereas 6 dB starts to be significant. 

Once the signal starts to fall off as you move away from the peak angle it starts falling off faster and faster per degree. In other words signal may drop off only 3 dB the first 15 degrees off the peak angle and then fall off another 3 dB when going from 15 to 20 degrees off the peak. 

This is not to say you can nor work 1200 miles with an antenna 1/4 wave high but it will not be as easy, as frequent and the signal will not be as strong as it would be with a higher antenna.

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