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

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MCRP 6-22D
x Chapter 8.  Antenna Farms
Command Post8-1
Tactical8-1
Main8-2
Rear8-2
Location Selection Considerations8-2
Doctrinal Considerations8-2
Tactical Considerations8-3
Technical Considerations8-5
Siting VHF Antennas8-6
Transmitting Antenna Site8-9
Receiving Antenna Sites8-11
Antenna Farm Internal Arrangement8-12
Frequency Band8-12
Antenna Selection and Placement8-12
Requirements8-14
Polarization8-15
Power and Signal Lines8-16
Antenna Farm Layout Principles8-16
Appendices
A  GlossaryA-1
B  References and Related PublicationsB-1 
						

							Chapter 1
Radio Principles
ELECTROMAGNETIC RADIATION
Electromagnetic radiation includes radio waves, microwaves, infra-
red radiation, visible light, ultraviolet waves, X-rays, and gamma
rays. Together they make up the electromagnetic spectrum. They all
move at the speed of light (186,000 miles/300 million meters per
second). The only difference between them is their wavelength (the
distance a wave travels during one complete cycle [vibration]),
which is directly related to the amount of energy the waves carry.
The shorter the wavelength, the higher the energy. Figure 1-1 lists
the electromagnetic spectrum components according to wavelength
and frequency (the number of complete cycles [vibrations] per sec-
ond). A portion of the spectrum which is used for HF, VHF, and
UHF radio communication has been expanded to show more detail.
Figure 1-1. Electromagnetic Spectrum.VISIBLE
UVX-RAYGAMMA-
RAYCOSMIC-
RAY
3MHz
30MHz
300MHz
3GHz
HF
VHF
UHFIR RADIO 
						

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MCRP 6-22D
RADIO WAVES
Radio waves propagate (travel) much like surface water waves.
They travel near the Earth’s surface and also radiate skyward at var-
ious angles to the Earth’s surface. As the radio waves travel, their
energy spreads over an ever-increasing surface area. A typical radio
wave has two components, a crest (top portion) and a trough (bottom
portion). These components travel outward from the transmitter, one
after the other, at a consistent velocity (speed). The distance between
successive wave crests is called a wavelength and is commonly rep-
resented by the Greek lowercase lambda (l) (see fig. 1-2).
Figure 1-2. Radio Wave.
Frequency
Radio waves transmit radio and television (TV) signals. They have
wavelengths that range from less than a centimeter to tens or even
hundreds of meters. Frequency modulated (FM) radio waves are
shorter than amplitude modulated (AM) radio waves. A radio
wave’s frequency equals the number of complete cycles that occur
in 1 second. The longer the cycle time, the longer the wavelengthSTRENGTHTIME OR DISTANCEONE CYCLE
WAVELENGTH
PEAK
PEAK 0 
						

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1-3
and the lower the frequency. The shorter the cycle time, the shorter
the wavelength and the higher the frequency.
Frequency is measured and stated in hertz (Hz). A radio wave fre-
quency is very high. It is generally measured and stated in thousands
of hertz (kilohertz [kHz]), in millions of hertz (megahertz [MHz]),
or sometimes in billions of hertz (gigahertz [GHz]).  
Frequency Calculation
For practical purposes, the velocity of a radio wave is considered to
be constant, regardless of the frequency or the amplitude of the
transmitted wave. To find the frequency when the wavelength is
known, divide the velocity by the wavelength.
To find the wavelength when the frequency is known, divide the
velocity by the frequency. 
Frequency Bands
Frequency spectrum designations are—1 Hz=1 cycle per second
1 kHz=1 thousand cycles per second
1 MHz=1 million cycles per seconds
1 GHz=1 billion cycles per second
Frequency (hertz)=300,000,000 (meters per  second)
Wavelength (meters)
Wavelength (meters)=300,000,000 (meters   per   second)
Frequency (hertz)
HFVHFUHF
3 to 30 MHz30 to 300 MHz300 to 3,000 MHz/3GHz 
						

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MCRP 6-22D
HF is used primarily for long-range communications. An HF signal
is reflected by the outermost portion of the atmosphere, the iono-
sphere. VHF is used for short-range communications. To use VHF,
it is necessary to be able to visualize a direct line of sight (LOS)
between the transmitter and receiver. This limits UHF to distances
that are not much greater than the distance to the horizon, assuming
that there are no massive obstructions in the LOS. When the LOS
path exists and VHF transmission is possible, VHF is always pre-
ferred to HF because a VHF signal can be made to follow a much
narrower and more direct path to the receiver. UHF is a third type of
transmission. UHF transmission is like VHF in that both follow the
direct or LOS path. But with the proper antenna, UHF transmission
can be made to follow an even narrower path to the receiver than
VHF.
Each frequency band has unique characteristics. The ranges and
power requirements shown in table 1-1 are for normal operating
conditions (i.e., proper siting and antenna orientation and correct
operating procedures). Ranges will change according to the condi-
tion of the propagation medium and the transmitter output power.
 
Tactical SCRs operate in the three military radio frequency bands
shown in table 1-2.  Table 1-1. Frequency Range Characteristics.
BandGround Wave
RangeSky Wave
RangePower 
Required
HF0–50 miles100–8000 miles.5–5 kW
VHF0–30 miles50–150 miles.5 or less kW
UHF0–50 milesN/A.5 or less kW 
						

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1-5
RADIO COMMUNICATION CIRCUIT
The radio equipment for communicating between two stations,
including the path the radio signal follows through the air, is a radio
link. A radio link consists of seven components:  transmitter, power
supply, transmission lines, transmitting antenna, propagation path,
receiving antenna, and receiver.
 Table 1-2. Ground SCRs.
Frequency 
BandMAGTF SCR 
Equipment UsedOperating 
Frequency 
RangeTypical
Application
HFAN/PRC-104
AN/GRC-193
AN/MRC-1382–29.999 
MHzRadio LOS and 
beyond/long range
VHFAN/PRC-68
AN/PRC-119
AN/VRC-88 (A, D)
AN/VRC-89 (A, D)
AN/VRC-90 (A, D)
AN/VRC-91 (A, D)
AN/VRC-92 (A, D)
AN/GRC-213
AN/MRC-14530–88 MHzRadio LOS and 
relay/retransmis-
sion
AN/PRC-113
AN/VRC-83116–150 MHzCritical LOS 
(ground to air)
UHFAN/PRC-113
AN/VRC-83
AN/GRC-171225–400 MHzCritical LOS 
(ground to air)
AN/PSC-3
AN/PSC-5SATCOM footprint 
						

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MCRP 6-22D
The transmitter generates a radio signal. The power supply provides
power for the operating voltage of the radio (battery or generator).
The transmission line delivers the signal from the transmitter to the
transmitting antenna. The transmitting antenna sends the radio
signal into space toward the receiving antenna. The path in space
that the radio signal follows as it goes to the receiving antenna is the
propagation path. The receiving antenna intercepts or receives the
signal and sends it through a transmission line to the receiver. The
receiver processes the radio signal so it can be heard (fig 1-3). 
The radio operator’s objective is to provide the strongest possible
signal to the receiving station. The best possible signal is one that
provides the greatest signal-to-noise (S/N) ratio at the receiving
antenna. 
To implement a radio communications circuit it is necessary to—
•Generate and radiate an electromagnetic wave modulated with
information (e.g., voice, Morse code).
•Make the wave propagate efficiently from the transmitting
antenna to the receiving antenna.
•Intercept the wave by using a receiving antenna.
•Demodulate the energy so that the information originally trans-
mitted becomes available in a useful form.
Choosing the right antenna and matching its characteristics to the
best propagation path are the two most important factors in setting
up a communications circuit. The weakest link in the communica-
tions circuit is the wrong propagation path. The best transmitter,
antenna, and receiver are of little use if the frequency is wrong or
the propagation path is improper. 
						

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1-7TRANSMISSION
LINESTRANSMITTING 
     ANTENNAPROPAGATIONPATH    RECEIVING      ANTENNAPOWERSUPPLYTRANSMITTERRECEIVERFigure 1-3. Typical Radio Link. 
						

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MCRP 6-22D
PROPAGATION FUNDAMENTALS
Earth’s Atmosphere
Propagation usually takes place within the Earth’s atmosphere. The
atmosphere surrounding the Earth is divided into several layers,
each possessing unique characteristics. The first layer, starting at
the Earth’s surface and extending to a height of about 10 kilometers
(km), is the troposphere. In this layer, the air temperature decreases
with altitude at the rate of about 2.5°C every 300 meters. 
The second layer of the atmosphere is the stratosphere, which occu-
pies an altitude range extending from about 10 km to 50 km. This
layer of air remains at a nearly constant temperature of about -65°C. 
Beginning at about 50 km and extending upward to more than 500
km is the ionosphere. The ionosphere gets its name because the
molecules of its atmosphere are ionized, i.e., electrons have been
stripped away from atoms by the constant bombardment of the
Sun’s rays and other high energy particles released by the Sun.
Because of the large quantities of free electrons, the ionosphere is
capable of interacting strongly on radio waves traveling through it.
Radio Wave Propagation 
There are two principal ways radio waves travel from the transmit-
ter to the receiver. One is by ground wave, directly from the trans-
mitter to the receiver. The other is by sky wave, up to the
ionosphere and refracted (bent downward) back to the Earth. Short-
distance, all UHF, and upper VHF transmissions are by ground
waves. Long-distance transmissions are principally by sky waves.
SCR sets can use either ground wave or sky wave propagation for
communications.  
						

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1-9
Ground Wave Propagation. Radio communications using ground
wave propagation do not use or depend on waves refracted from the
ionosphere (sky waves). Ground wave propagation is affected by
the Earth’s electrical characteristics and by the amount of diffrac-
tion (bending) of the waves along the Earth’s curvature. The ground
wave’s strength at the receiver depends on the transmitter’s power
output and frequency, the Earth’s shape and conductivity along the
transmission path, and the local weather conditions. The ground
wave includes three components: the direct wave, the ground
reflected wave, and the surface wave (fig. 1-4).
Figure 1-4. Ground Wave.
Direct Wave. The direct wave travels directly from the transmitting
antenna to the receiving antenna. The direct wave is limited to the
LOS distance between the transmitting antenna and the receiving
antenna plus the short distance added by atmospheric refraction and
diffraction of the wave around the Earth’s curvature. This distance
can be extended by increasing the transmitting or the receiving
antenna height, or both. GROUND REFLECTEDDIRECT WAVESURFACE   WAVE             WAVE