personnel qualification standard (pqs) - I Marine Expeditionary ...

Communications 114
High Frequency Radio Environmental Limitations
The primary limiting factors when using HF radios are frequency
allocation and management and bandwidth availability. Frequency
allocation and management is concerned with frequency, time of day, time
of year, and location. The ability to reflect HF radio waves off the
ionosphere to a distant location is in a constant state of flux because of
activity in the ionosphere. The Sun’s radiation causes disturbances in the
ionosphere, with most changes taking place in what is known as the F
layer . Sunrise and sunset can be the most difficult times for HF
communications. The F layer splits into two separate layers around sunrise
and recombines into one layer around sunset. These splits affect
transmission distances as the area “skipped over” increases and decreases.
At times, solar storms can eliminate all HF communications. HF
transmission paths must be constantly monitored to achieve a dependable
HF link. HF radio data communications capabilities are limited by the
bandwidth that is imposed by legal constraints and the physics of the
spectrum. The bandwidth available in the HF spectrum limits the channel
bandwidth, which limits data throughput.
High Frequency Propagation
There are two modes of propagation in HF: ground wave and sky wave.
See figure 2-2.
Ground Wave. Ground wave propagation involves the transmission of a
signal along the surface of the ground. The maximum ground wave range
for most tactical HF communications is about 20 to 30 kilometers (12 to
22 miles) for manpack equipment and 80 to 100 kilometers for high-power
vehicular and van equipment. The range may be decreased by heavy
vegetation (e.g., Camp Lejeune), mountainous terrain (e.g., Camp
Pendleton), or dry desert soil (e.g., Twenty-nine Palms). A ground wave
circuit will generally be free of fading and may last for the entire 24-hour
period without the need to change frequencies.
114-7