Thursday, October 28, 2010

When it comes to HF antennas, how important is the elevation angle?...

Q When it comes to HF antennas, how important is the
elevation angle?

A Presuming that you are interested in working worldwide DX on the HF bands, the vertical (elevation) angle of maximum radiation is of considerable importance. An elevation angle of 5° is very shallow, while 90° is straight up (not a good angle for long-distance communication!). You want your radiation pattern to be at a low elevation angle so that the signal energy will be refracted by the ionosphere in such a way that it propagates as far as possible (see Figure 1).

Tables 1, 2 and 3 from The ARRL Handbook show optimum elevation angles from locations in the continental US. These figures are based on statistical averages over all portions of the solar sunspot cycle.

Since low angles usually are most effective, this generally means that horizontal antennas should be high—higher is usually better.

Figure 1—The elevation angle advantage. If your signal takes off at a high elevation angle (A), it won’t propagate very far. Lower the angle (B), and the increase in distance can be considerable. A wavelength of height at a particular frequency results in a peak elevation angle of about 15°. 

From QST January 2001