Frequency (3 MHz - 30MHz):
wide variety of propagation modes are useful on the HF bands. The lowest
two bands in this range share many daytime characteristics with 160m. The
transition between bands primarily useful at night or during the day
appears around 10 MHz. Most long-distance contacts are made via F2 layer
skip. Above 21 MHz, more exotic propagation, including TE, sporadic E,
aurora and meteor scatter, begin to be practical.
lowest HF band is similar to 160m in many respects. Daytime absorption is
significant, but not quite as extreme as at 1.9 MHz. High-angle signals
may penetrate to the E and F layers. Daytime communication range is
typically limited to 400 km by ground-wave and skywave propagation. At
night, signals are often propagated halfway around the world. As at 1.8
MHz, atmospheric noise is a nuisance, making winter the most attractive
for the 80m DXer.
popular 40m band has a clearly defined skip during the day. D-layer
absorption is not as severe as on the lower band, so short-distance skip
via E and F layers is possible. During the day, a typical station can
cover a radius of approximately 800 km. Ground-wave propagation is not
important. At night, reliable worldwide communication via F2 layer is
common on the 40m band. Atmospheric noise is less troublesome than on 160m
and 80m, and 40m DX signals are often of sufficient strength to override
even high-level summer static. For there reasons, 40m is the
lowest-frequency amateur band considered reliable for DX communication in
all seasons. Even during the lowest point in the solar cycle, 40m may be
open for worldwide DX throughout the night.
30m band is unique because it shares characteristics of both daytime and
nighttimebands. D-layer absorption is not a significant factor.
Communication up to 3000 km is typical during daytime. and this extends
halfway aroung the world via all-darkness paths. The band is generally
open via F2 on a 24-hour basis, but during a solar minimum, the MUF on
some DX paths may drop below 10MHz at night. Under this conditions 30m
adopts the characteristics of the daytime bands at 14 MHz and higher. The
30m band shows the least variation in conditions ober the 11-year
solar cycle, thus making it generally useful for long distance
20m band is traditionally regarded as the amateurs' primary long-haul DX
favorite. Regardless of the 11-year solar cycle, 20m can be depended on
for at least a few hours of worldwide F2 propagation during the day.
During solar maximum periods, 20m will often stay open to distant
locations throughout the night. Skip distance is usually appreciable and
is always present to some degree. Daytime E-layer propagation may be
detected along very short paths. Atmospheric noise is not a serious
consideration, even in the summer. Because of its popularity, 20m tend to
be very congested during daylight hours.