Practical_Antenna_Handbook_0071639586

66 p a r t I I : F u n d a m e n t a l s
Figure 2.35 Azimuthal map centered on Washington, D.C. (Courtesy of The ARRL Antenna Book.)
For a while, antenna manuals published by the ARRL included a family of great
circle maps centered on selected population centers around the world. Nowadays, plotting
software is readily available for download from the Internet at no cost, either
stand-alone or as part of a larger log-keeping and station control package. Whether
using multiple hard-copy maps or recentering a software-generated map with a few
keystrokes (to enter new latitude and longitude coordinates for the center of the map),
seeing the world of HF radio propagation through the eyes of your fellow hobbyists on
other continents is often highly informative.
Airplane crews and DXers both consult great circle maps to ascertain the compass
heading that corresponds to the shortest distance between two points on (or just above)
the surface of the earth. The navigator wants to get the airplane from here to there in the
shortest possible time and with the smallest fuel expenditure; the radio operator wants
to get a signal from here to there with the least path loss possible. As a general rule, the