HF radio transmission
22 2110 SSB Transceiver Reference Manual
HF radio transmission
The HF band is the range of frequencies between 3 and 30 MHz. HF transceivers usually
cover a frequency range of 1.6 to 30 MHz.
Codan HF transceivers transmit on single sidebands. This reduces the power required to
send HF signals and increases the number of channels available within the HF spectrum.
HF transceivers are primarily used for long-range communication where distances of
3000 km (1800 mi) and more are possible. Obstructions such as buildings and
mountains have little effect on long-range communication. HF radio can cover such large
distances because of the way the transmitted radio signal propagates.
HF radio waves propagate in three ways simultaneously:
• ground wave
• direct wave
• sky wave
Ground wave
The ground wave travels near the ground for short distances, typically up to 100 km
(60 mi) over land and 300 km (190 mi) over sea. The distance covered depends upon the
operating frequency, transmission power and type of terrain.
Direct wave
The direct wave travels in a direct line-of-sight from the transmitter to the receiver.
Sky wave
The sky wave is the most important form of HF propagation. The radio wave is
transmitted toward the sky and is reflected by the ionosphere to a distant receiver on
earth.
The reflective properties of the ionosphere change throughout the day, from season to
season, and yearly.
Figure 1: The reflective properties of the ionosphere
ionosphere
transmitter
receiver
emitted
HF wave
reflected
HF wave
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