If the tactical situation permits, a simple half-
wave dipole or the Near Vertical Incidence Skywave
(NVIS) twin dipole antenna can be used between 2 and
This section provides information to assist the
12 to extend the range of the radio considerably )by
utilizing the "skip" phenomenon. In this mold the radio
mode, and site for achieving best communication with
waves are bounced off the ionosphere and back to the
this radio set. Refer to Appendix II for, information on
earth's surface providing coverage to 300 miles or more.
propagation of radio waves and some situational
The twin dipole may' )be used at frequencies above 12
examples for optimizing radio comication.
NMHz, but automatic tuning may not work at all
OPTIMIZING COMIMUNICATION WITH THE
frequencies. The nature of the dipole or NV'IS antenna
optimizes the skip effect but final results depend on
existing propagation characteristics.
The readability and effectiveness of radio
communications in the high frequency (HF) range is
When using an antenna that has directional
dependent on several factors..
characteristics, try to orient the antenna so it is most
sensitive in the direction toward the other station. For
1. Type of antenna used
example, a dipole antenna is most effective in a direction
2. Operating frequency selected
perpendicular to the wire. The NVIS antenna is omri-
3. Terrain around transmitting site
directional (same sensitivity in all directions), so
4. Time of day'
orientation of the antenna is not important.
5. Geographic location and distance between
A list of standard and alternate antennas that
6. Atmospheric conditions
can be used with the AN/PRC-104, with the major
7. The effects of the ionosphere on radio waves
characteristics of each, is shown below.
The radio operator can control, to some
Omnidirectional (360 degree
degree, only the first four or five of these factors. The
others affect propagation characteristics and background
interference, and are beyond operator control.
Easily and quickly assembled and
antenna and frequency are the most important factors
under operator control, and should be selected to best
suit the propagation characteristics and distance of the
Several frequencies will probably have been
Very poor gain; limited range (<10
assigned from upper echelon.
They will have been
mi) over land, even in hill terrain.
selected in various portions of the band in order to allow
Range may be better under good
a frequency change when propagation conditions
ANTENNA SELECTION (Figure 2-2).
Requires fairly large clear area 60
feet square) for proper erection
The field environment, tactical situation, and
range required determine the antenna selection. If the
Good gain; extended range (0 to
radio set is to be used while on the move (manpack
operation), the whip antenna supplied with the antenna is
used. For most short range requirements using ground
Bidirectional (perpendicular to
wave, the whip antenna will be satisfactory up to 10 miles
over land. However, over sea water, this antenna will
provide reliable communications up to 100 miles.