Practical_Antenna_Handbook_0071639586

C h a p t e r 2 : r a d i o - W a v e P r o p a g a t i o n 79
their ability to work DX find that a handful of profiles, one in the direction of each major
population area, is sufficient. For example, a DXer or contest operator in the northeastern
United States would profit most from profiles for 45 degrees (Europe, the Near East,
and central Asia), 100 degrees (Africa), 170 degrees (Central and South America), 270
degrees (Australia and New Zealand), and 345 degrees (Western Australia, Japan, and
the Far East). For this amateur, the 270-degree profile would also serve to identify terrain
issues for most domestic U.S. beam headings, but amateurs in other parts of the
country might need a sixth profile for that.
Of course, the greatest and best use of HFTA profiles is before buying a site intended
to be a stellar radio location! But it also has great utility after the fact for identifying how
high one’s antennas for any given band must be to optimize the probabilities associated
with the statistical nature of long-distance ionospheric propagation.
The Magic of Radio
Because so many of the known modes of propagation depend on external factors that
are constantly varying over time, our ability to communicate—especially via the ionosphere—is
a statistical one. Just because we were able to pick up the microphone and
talk with another hobbyist halfway around the world on 20 m yesterday doesn’t mean
we’ll be able to do it again today. The work we do to improve our antennas, the reading
we do to understand the subtleties of propagation, the time we spend tuning across the
bands, analyzing the noises we hear, listening for the weakest of signals—all are intended
to tilt the odds more toward our favor. But ultimately we are at the mercy of
Mother Nature, who is not above throwing us a curveball every now and then.
Yet, for many of us, it is this statistical uncertainty that is at the very heart of the joy
we find in communication by radio. For many, it is the unique sound of a weak signal
fading in and out of the band noise that is the magic of radio. And, as in poker or bridge,
where the number of different hands that can be dealt far exceeds the number that can
be played in one’s lifetime, so too is there a nearly infinite variety of possible band conditions
awaiting us each time we sit down at our receiver and put on the headphones.
The unpredictability of ionospheric HF propagation is without a doubt one of the lifelong
draws of radio communications for tens of thousands, the author included. It’s
magic!