Figure 2-4. Space wave propagation.
(1) The primary path of the space wave is directly from the transmitting antenna to the
receiving antenna. Consequently, the receiving antenna must be located within the radio horizon of the
transmitting antenna. Because space waves are refracted slightly, even when propagated through the
troposphere, the radio horizon is actually about one-third farther than the line-of-sight (natural) horizon.
(2) Although space waves suffer little ground attenuation, they nevertheless are susceptible
to fading. Because space waves actually follow two paths of different length (direct path and ground-
reflected path) to the receiving site, they may arrive in or out of phase. If these two component waves
are received in phase, the result is a reinforced or stronger signal. Conversely, if they are received out of
phase, they tend to cancel one another, resulting in a weak or fading signal.
4. Engineering considerations for ground wave systems. There are a number of factors that affect
ground wave propagation. Some of these are:
a. Frequency. Using lower frequencies results in less ground loss and increases range.
b. Antenna characteristics. Using vertical polarization, when possible, reduces the effect of the
Earth "shorting out" the electric field of the wave.
c. Power. Increasing the power output result in greater distance.
d. Time of day. Sources of noise (natural and manmade) affect radio wave propagation at
different times of the day.
e. Terrain. The best propagation is achieved over conductive terrain.
absorbs less wave energy.