Quickly assemble and erected
requires two vertical supports
2-31. Site selection is particularly important for short-
range, ground wave communications. The existing
Good gain extended range (0 to
tactical situation will determine how much of a selection
300 miles and beyond)
is available. Generally, the best communications will be
obtained if the transmitting site is clear of all
obstructions, located in an area with good ground
conductivity (wet or plowed ground) and as high above
ground as possible. Several locations in the same
general vicinity should be checked as possible sites. A
Quickly assembled and erected
slight change in antenna location can make a substantial
requires only one vertical support
difference in effectiveness.
Fair gain ; moderately extended
2-32. Avoid areas near sources of electrical
range (to 1000 miles)
interference such as power lines, radar sets, field
hospitals with X-ray machines, etc. Also avoid large
structures having metallic content bridges, tanks, steel
reinforced buildings, etc.
If enemy jamming is a
2-27. The primary considerations when selecting an
possibility, the site should be selected so that a large
operating frequency are the distance b)between the
object or terrain feature is situated between the radio and
sending and receiving stations, and the time of day'.
the jamming source. This minimizes the effects of the
Refer to Appendix II, figures A24 and A25 which relate
jamming station and makes it more difficult to locate your
the relative effective less of communications for four sub-
transmitter using direction finding equipment.
band segments to the tile of day. These figures are
based on average propagation characteristics for the
MODES OF OPERATION.
sub-ands and are intended for rise only as a general
guide. For detailed frequency planning over a specific
2-34. The radio set mode of operation is dependent
time period, propagation prediction charts are able from
upon tactical requirements. The following conditions are
several government agencies. ("Intermediate and Short
examples of the types of conditions which may be
Headquarters U.S. Army Communications Electronics
Engineering Installation Agency, Ft. Huachuca, Arizona
2-35. NORMAL COMMUNICATIONS. For two-way.
communications under normal circumstances, the radio
set should i be operated on _R. This selection permits
2-28. Another consideration selecting an operating
the radio to transmit and receive voice (or cw
frequency is the atmospheric condition. If rain or other
communications on any of the 280,000 frequency
precipitation is present, signals at the lower end of the hf
band may be degraded by atmospheric noise while the
higher frequencies will be affected to a lesser degree.
2-36. RADIO SILENCE. When field conditions
Therefore, higher frequencies will provide more
require that no radio transmissions be made, the node
effective communications in inclement weather.
selected should be V-RCV or DRC,V. These modes
render the radio set passive and inhibit the modulator in
2-29. The most useful phenomenon in radio wave
order to prevent transmission. When V-RCV is selected,
propagation is the "skip" effect. This effect occurs
the radio set receives voice (or cw) but cannot transmit.
l)because the layers of the ionosphere become ionized
When DRC: is selected, the radio set receives data
l)y the ultraviolet radiation of the sun. This level of
information but does not transmit data.
ionization determines the highest frequency for skip over
a given distance. Generally, the higher the ionization
2-37. Data Communication. When field conditions
level, the higher the fre(quency that can be used in "skip"
require transmitting and receiving data, the radio set
mode and therefore the broader the range of frequencies
mode selectetd is D-TR. This Mode permits two-way