The sloping long-wire antenna and a sloping quarter-wave wire antenna
have similar performance characteristics.
Since we are using short
distance sky wave, again, antenna orientation is not a factor. Let's
take a look at the ground wave charts to see how far our ground wave
will reach.
Turn to the index to ground wave ranges on page 158.
Look down the left side to find our type of service, RTTY, single
channel, FSK, 60 W/M.
Next, look across the top for our power in
watts, 300 to 499. Where these two columns intersect, is the column
number for our charts. We will use 7. Now, turn to our 15-foot whip
antenna chart on page 159, the 32-foot whip on page 160, and sloping-
wire on page 161. As you can see, our ground wave range for 3 to 5.7
MHz is approximately 14 to 37 miles.
During a 24-hour period this
means that ground wave propagation cannot be used for this circuit.
b. Situation 2.
(1) Let us assume that we have a radio circuit in which our
stations are 100, 750, and 1500 miles away from the net control
station (NCS).
We are using an AN/GRC-142 in radioteletype mode
during a low sunspot period.
Let's select two frequencies for 24-
hour operation. One of the problems in operating in a net like this
is that some of the stations might be close while others are far
away. Will the same two frequencies work for all stations all of the
time? Probably not. You might have to set up two or three nets with
two or three radios at the NCS location to accommodate the stations
of varying distance. Of course, it is easy to say. However, if you
don't have the resources, what will you do? Select frequencies that
provide communication for the majority of stations and then rely on
relaying to get the traffic through.
The stations with which you
will have the most difficulty are the closest stations, while the
ones further away will be easier to communicate with.
(2) We will use a doublet at least 40 feet high above the
ground.
Long distance communications is best when our antenna is
over a half wavelength (at the lowest frequency, if possible) above
the ground. The antenna should be broadside to the majority of the
stations. Let's find the highest and lowest FOT and then the highest
and lowest LUF for 100, 750, and 1500 miles.
123
Previous Page
