OPERATING CONSIDERATIONS

TM 11-5820-919-12

SECTION II

OPERATING CONSIDERATIONS

2-16.

GENERAL.

2-23.

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

2-17.

This section provides information to assist the

12 to extend the range of the radio considerably )by

operator in selecting the proper antenna, frequency,

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

2-18.

OPTIMIZING COMIMUNICATION WITH THE

frequencies. The nature of the dipole or NV'IS antenna

AN/PRC-104.

optimizes the skip effect but final results depend on

existing propagation characteristics.

2-19.

The readability and effectiveness of radio

communications in the high frequency (HF) range is

2-24.

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

stations

2-25.

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.

2-20.

The radio operator can control, to some

WHIP ANTENNA

Omnidirectional (360 degree

degree, only the first four or five of these factors. The

radiation pattern)

others affect propagation characteristics and background

interference, and are beyond operator control.

The

Easily and quickly assembled and

antenna and frequency are the most important factors

erected

under operator control, and should be selected to best

suit the propagation characteristics and distance of the

Excellent portability

link.

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

propagation conditions.

change.

NEAR VERTICAL

Omnidirectional

INCIDENCE

2-21.

ANTENNA SELECTION (Figure 2-2).

SKYWAVE (NVIS)

Requires fairly large clear area 60

feet square) for proper erection

2-22.

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

300 miles)

operation), the whip antenna supplied with the antenna is

used. For most short range requirements using ground

HALF-WAVE

Bidirectional (perpendicular to

wave, the whip antenna will be satisfactory up to 10 miles

DIPOLE

wire)

over land. However, over sea water, this antenna will

provide reliable communications up to 100 miles.

Good portability

2-5