The 15 Meter Dipole and elevation angles

The higher bands (15 and 10 meters) are now starting to open for DX.
If you do not have an antenna for these bands yet, I suggest building a simple dipole fed with coax. For lengths of up to 100 feet, RG 8X is not a bad choice. The loss for 100 feet of RG8 X should be less than 2 dB at 15 meters. Less loss will require larger and heavier coax. I feel it is most important to get the dipole outdoors if possible. It does not have to be real high as long as it is away from any nearby objects, especially metalic objects. On 15 meters I consider 20 to 25 feet high. That height puts the antenna a halfwave above the ground. Any antenna that is a halfwave above the ground is frequently a better general purpose antenna than one twice as high. I will go into more detail about antenna patterns at a later date. For now let's just say that I think the magic number for the height of a horizontal antenna (not a vertical antenna) is one half wavelength!
That's 16 feet for 10meters, 22 feet for 15 meters and 33 feet for 20 meters. Antennas that are in the clear, away from any nearby objects work very well at these heights. One problem may be 16 feet on 10 meters. It may be hard to get a 10 meter antenna in the clear at only 16 feet. In that case the best solution is to double the height to 32 feet. The same goes for the other bands. Doubling the height to one full wavelength will give added performance at long distances but will produce a reduction in performance at an intermediate distance. I am most interested in DX on 15 meters, so I chose to put my 15 meter dipole at about 44 feet. That height is acheivable because I have some nice tall trees I can use for support. I chose to do the same for my 10 meter dipole. If I ever put up a tower again I expect to only go about 35 feet. I have had my 20 meter beam at 70 feet and if I put it back up I think it will do almost as well at a halfwave as at one full wave. I also will not have the null at a vertical angle of 30 degrees.
All horizontal antennas will exhibit a decrease in performance or null at an elevation angle of 30 degrees. This elevation angle translates to loss of performance at distances of 350 and 700 miles (1 or 2 hop E skip) and distances of 550 and 1100 miles for F layer skip. These numbers vary quite a bit because they depend on the height of the ionospheric layer layers. These heights vary with the time of day and sun activity. Variations in the F layer height could cause this distance of reduced performance for a horizontal antenna one full wavelength above the ground to vary form about 400 to 800 miles.
If you are most interested in these distances be sure your antenna is not a full wavelength above the ground. A horizontal antenna half as high (one-half wavelength) will have its maximum performance at these distances and (all other things being equal) could actually be 10 dB stronger than the higher antenna!