1: Introduction
PRC1099A-MSOP 1-5
The low frequencies, below 3 MHz, will normally be restricted to short ranges
during the day. At night, longer ranges (3 to 400 kilometers) are possible, but
interference and static may be major problems. Good antennas and high
power are essential for anything but the shortest distances.
The medium frequencies from 3 to 5 MHz may be a good choice for moderate
distances (3 to 400 kilometers) during the day. At night, considerable
distances are possible, although static will be a frequent problem during
summer months. The physical length of a good antenna is still quite long, and
it is difficult to achieve good efficiencies with whip antennas in this range.
The medium frequencies from 5 to 11 MHz are the most popular for
communications up to 1000 kilometers. Good ranges are possible during the
day with the higher frequencies being favored for the longer distances.
Communications may become more difficult at night with interfering signals
from all over the world.
The higher end of the spectrum, above 12 MHz, is favored for long distance
communications. The propagation will be severely affected by the ionosphere
and expert advice is essential in choosing the correct frequencies for long
distance operation. For example, frequencies as high as 30 MHz may be used
for worldwide communications during the peak of the sunspot cycle.
However, during periods of low sunspot activity, this frequency range will be
completely dead. It is important to remember that at the higher frequencies
there can be skip zones; and a strong signal may be received from 2000
kilometers away, while closer stations cannot be heard.
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