TM 11-5985-379-14&P
Sky-Wave Versus Surface-Wave Propagation.
Figure 3-5.
an acceptable loss of 4.5 dB due to ground (Bever-
i n c r e a s e s , a larger part of the input signal is
age mode). This requires an antenna height of 0.035
radiated in the dipole mode. These resistances are
typical of these encountered over average ground.
= 4.5 dB) .
An effective height of 0.035 wavelength is about
The efficiency of the dipole mode is then the ratio
10 feet at 3.5 MHz.
of the dipole mode resistance to the total input
r e s i s t a n c e . T h e gain of the horizontal dipole
An effective height of 10 feet can be achieved by
antenna is then
a horizontal dipole mounted between two 10-foot
towers or by a sloping dipole mounted from a taller
Total Resistance
G = 7-10 log
single mast at its center. The latter is desirable
Dipole Mode Resistance.
for tactical requirements because weight, volume,
and erection time need be minimized. The single
The required antenna gain was previously found to
m a s t may also serve as a very low-loss trans-
b e +2 dBi. Assuming 0.5 dB transmission line
m i s s i o n l i n e feeding the dipole element. An
losses, 2.5 dBi is allowed for the antenna, leaving
3-6
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