Figure 3-5. Sky-Wave Versus Surface-Wave Propagation.

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) .

wavelength

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