U.S. Marine Corps Antenna Mcrp 6 22D Operating Instructions

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MCRP 6-22D
two conditions represent destructive and constructive combinations
of the reflected and direct waves.
Reflection from the ground at the common midpoint between the
receiving and transmitting antennas may also arrive in a construc-
tive or destructive manner. Generally, in the VHF and UHF range,
the reflected wave is out of phase (destructive) with respect to the
direct wave at vertical angles less than a few degrees above the
horizon. However, since...

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over LOS paths because there tends to be less phase difference
between direct and reflected waves. The difference is usually less
than 10 dB, however, in favor of vertical polarization.
Diffraction
Unlike the ship passing beyond the visual horizon, a radio wave
does not fade out completely when it reaches the radio horizon. A
small amount of radio energy travels beyond the radio horizon by a
process called diffraction. Diffraction also occurs when a...

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MCRP 6-22D
TV station are diffracted by the mountain ridge and bent downward
in the direction of the village. It is emphasized, however, that the
energy decays very rapidly as the angle of propagation departs from
the straight LOS path. Typically, a diffracted signal may undergo a
reduction of 30 to 40 dB by being bent only 5 feet by a mountain
ridge. The actual amount of diffracted signal depends on the shape
of the surface, the frequency, the diffraction...

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antenna and a distant receiving site. The effects of such ducting can
be seen frequently during the year in certain locations where TV or
VHF FM stations are received over paths of several hundred kilo-
meters. The total path loss within such a duct is usually very low
and may exceed the free space loss by only a few dBs.
It is also possible to communicate over long distances by means of
tropospheric scatter. At altitudes of a few kilometers, the air...

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MCRP 6-22D
Natural Noise
Natural noise has two principle sources: thunderstorms (atmo-
spheric noise) and stars (galactic noise). Both sources generate
sharp pulses of electromagnetic energy over all frequencies. The
pulses propagate according to the same laws as manmade signals,
and receiving systems must accept them along with the desired sig-
nal. Atmospheric noise is dominant from 0 to 5 MHz, and galactic
noise is most important at all higher frequencies....

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with respect to the receiver input terminals (zero voltage across ter-
minals), and this noise will not be received. Near-perfect balance is
difficult to achieve, but any balance helps. 
Other ways to avoid manmade noise are to locate the most trouble-
some sources and turn them off, or move the receiving system away
from them. Moving a kilometer away from a busy street or highway
will significantly reduce noise. Although broadband receiving
antennas...

Chapter 2
Antenna Fundamentals
All radios, whether transmitting or receiving, require some sort of
antenna. The antenna accepts power from the transmitter and
launches it into space as an electromagnetic or radio wave. At the
receiving end of the circuit, a similar antenna collects energy from
the passing electromagnetic wave and converts it into an alternating
electric current or signal that the receiver can detect. 
How well antennas launch and collect electromagnetic waves
directly influences...

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MCRP 6-22D
Section I. Concepts and Terms
To select the right antennas for a radio circuit, certain concepts and
terms must be understood. This section defines several basic terms
and relationships which will help the reader understand antenna
fundamentals. These include: forming a radio wave, radiation fields
and patterns, polarization, directionality, resonance, reception, reci-
procity, impedance, bandwidth, gain, and take-off angle.
FORMING A RADIO WAVE
When...

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upward on the wire to the top, where they have no place to go and
are bounced back toward the lower end. As the electrons reach the
lower end in phase, i.e., in step with the radio energy then being
applied by the transmitter, the energy of their motion is strongly
reinforced as they bounce back upward along the wire. This regen-
erative process sustains the oscillation. The wire is resonant at the
frequency at which the source of energy is...

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MCRP 6-22D
 
Figure 2-1. Radiation Fields.
Radiation Patterns
The radio signals radiated by an antenna form an electromagnetic
field with a definite pattern, depending on the type of antenna used.
This radiation pattern shows the antenna’s directional characteris-
tics. A vertical antenna radiates energy equally in all directions
(omnidirectional), a horizontal antenna is mainly bidirectional, and
a unidirectional antenna radiates energy in one direction....