The importance of understanding basic
VHF and UHF propagation cannot be overemphasized. Unlike DXing on the
shortwave bands, you can't just turn on the receiver, tune around, and expect
to get a faraway station. On VHF and UHF the normal situation is no DX
--- until some abnormal propagation occurs. Also, unlike shortwave, there are
several different kinds of propagation above 30 MHz. To DX effectively,
you should be able to evaluate what you pick up. This requires being
able to tell one type of propagation from another. Fortunately, the
propagation modes differ sufficiently from one another that by combining a
little experience with the descriptions to follow, you should seldom have any
difficulty assigning one definite propagation mode to each DX catch.
Why is this so important? If all you
care about is the quantity of DX --- receiving each station once --- it may
not matter so much. But it does matter for quality. For example, over the
course of several years you may be able to pick up a given station by two, or
even three different propagation modes. One will undoubtedly be much rarer
than the other(s). For instance, a channel 2 TV station 1000 miles away is
relatively easy to see via sporadic E, while the same station is very seldom
subject to tropo propagation over such a distance. On the other hand, a
channel 7 TV station will seldom cover such a distance, but when it does it
will do so more readily by tropo than by sporadic E. So let's look at these
mechanisms to which we owe our hobby.
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