HF-90 Operation & Installation Guide
A
Not to scale
20 km 2,000 km 800 km
D C B
The following illustrations show the characteristics of
ground-wave and sky-wave propagation during the day time
and night time. Each illustration clearly shows the level of
the ionosphere.
In both illustrations Station A communicates with Stations
B, C and D. Propagation from Station A to B is via ground-
wave. You will notice how the time of day, and level of the
ionosphere, does not affect ground-wave.
Propagation from Station A to C and D is via sky-wave.
You will notice how the time of day, and level of the
ionosphere, affects sky-wave.
Under each diagram there are recommended working
frequencies listed. Please note that these will vary according
to time of year and other factors. They are intended only as
a guide and are subject to change.
5
Section 2.2
Ionosphere
A to B - Recommended working frequency is 3 MHz
A to C - Recommended working frequency is 7 - 9 MHz
A to D - Recommended working frequency is 13 - 16 MHz
DAY TIME:
Sun is higher
Ionosphere is
higher
Optimum
working
frequency is
higher
Radio propagation illustrated
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