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

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MCRP 6-22D
Ground Reflected Wave. The ground reflected wave reaches the
receiving antenna after being reflected from the Earth’s surface.
Cancellation of the radio signal can occur when the ground
reflected component and the direct wave component arrive at the
receiving antenna at the same time and are 180° out of phase with
each other.
Surface Wave. The surface wave follows the Earth’s curvature. It
is affected by the Earth’s conductivity and dielectric...

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Earth’s Surface Conductivity. The dielectric constant or Earth’s
surface conductivity determines how much of the surface wave
signal energy will be absorbed or lost. Although the Earth’s surface
conductivity as a whole is generally poor, the conductivity of vary-
ing surface conditions, when compared one with an other, would be
as stated in table 1-3. 
Sky Wave Propagation. Radio communications that use sky wave
propagation depend on the ionosphere to...

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MCRP 6-22D
The D layer exists only during the day and has little effect in bend-
ing the paths of HF radio waves. The main effect of the D layer is to
attenuate HF waves when the transmission path is in sunlit regions. 
The E layer is used during the day for HF radio transmission over
intermediate distances (less than 2,400 km/1,500 miles [mi]). At
night the intensity of the E layer decreases, and it becomes useless
for radio transmission.
The F layer exists at...

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1-13F1 & F2
F1 E 
D 
F2 COMBINE
F2 250-500 km (250-420 km at night)
F1 200-250 km
E     90-130 km
D       75-90 kmSUN
AT NIGHTF2F1E
DDAYLIGHT POSITIONSFigure 1-5. Ionospheric Structure. 

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MCRP 6-22D
Irregular Ionospheric Variations. In planning a communications
system, the current status of the four regular variations must be
anticipated. There are also unpredictable irregular variations that
must be considered. They have a degrading effect (at times blank-
ing out communications) which cannot be controlled or compen-
sated for at the present time. Some irregular variations are— 
•Sporadic E. When excessively ionized, the E layer often blanks
out...

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Frequency Characteristics in the Ionosphere. The range of long-
distance radio transmission is determined primarily by the ioniza-
tion density of each layer. The higher the frequency, the greater the
ionization density required to reflect radio waves back to Earth. The
upper (E and F) layers reflect the higher frequencies because they
are the most highly ionized. The D layer, which is the least ionized,
does not reflect frequencies above approximately...

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MCRP 6-22D
ionosphere’s height and density. The antenna’s height, in relation to
the operating frequency, affects the angle that transmitted radio
waves strike and penetrate the ionosphere and then return to Earth.
This angle of incidence can be controlled to obtain the desired cov-
erage area. Lowering the antenna height increases the angle of trans-
mission and provides broad and even signal patterns in a large area. 
Using near-vertical transmission paths is...

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reliability. Only when the signal level fades down below the back-
ground noise level for an appreciable fraction of time will increased
transmitter power or antenna gain yield an overall circuit improve-
ment. Choosing the correct frequency and using transmitting and
receiving equipment intelligently ensure a strong and reliable
receiving signal, even when low power is used.
Maximum Usable and Lowest Usable Frequencies. Using a
given ionized layer and...

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MCRP 6-22D
Propagation Prediction. Although a detailed discussion of propa-
gation prediction methods is beyond the scope of this publication, it
should be noted that propagation predictions can be obtained from a
system planning, engineering, and evaluation device (SPEED).
Other Factors Affecting Propagation
In the VHF and UHF ranges, extending from 30 to 300 MHz and
beyond, the presence of objects (e.g., buildings or towers) may pro-
duce strong reflections...

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Path Loss
Radio waves become weaker as they spread from the transmitter.
The ratio of received power to transmitted power is called path loss.
LOS paths at VHF and UHF require relatively little power since the
total path loss at the radio horizon is only about 25 decibels (dB)
greater than the path loss over the same distance in free space
(absence of ground). This additional loss results from some energy
being reflected from the ground, canceling part...