It will probably be impossible to select a frequency or frequencies
that will provide communications to all the stations all of the time.
We will select frequencies which will allow communications to the
middle-distance station (750 miles).
There will be times, probably
at night, when all stations hear, and other times when only one
station hears.
In that case, the station that hears must act as a
relay for the others.
For daytime, use any frequency between the
highest FOT 12.0 MHz and the highest LUF 7.2 MHz, probably in the
middle or 9.6 MHz.
For nighttime, any frequency between the lowest
FOT 4.5 MHz and lowest LUF 2.0 MHz will work (move to 3 MHz to escape
ship-to-shore stations).
To make communications better, a third
frequency might be considered. You can see from the LUF charts that
direct communication with station C (1500 miles) is less than 90%
reliable. Upon checking other antennas, you will find that they are
even less reliable.
(3) Suppose that we were forced to use a 32-foot whip for this
net.
What would be the consequences?
Ground wave would be out of
the question.
As you look at the LUF charts, you can see that the
overall reliability is very low, on the order of 50%. Station A (100
miles) is the one we will have the most trouble with. Station B (750
miles) will be doing a lot of relaying.
The reason that the
reliability of station A is poor is because a whip is a vertical
antenna and it favors sky wave with a low take-off angle. Station A
is too close for these low take-off angles and too far for ground
wave.
Station B is at the optimum range for a vertical antenna.
Even so, the reliability for a 32-foot whip is 60 to 80 percent. It
also radiates in all directions - another disadvantage.
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