only practical means of communicating with moving
vehicles, such as ships or aircraft. Also, radio
communication can span great distances in any or all
directions. It is the most practical system to use for
sending information to many points, as in broadcasting
to large numbers of ships or aircraft.
navigational aids. Navigation aids consist of many
types and are of varying complexity. They range from
simple radio direction finders to complex navigational
systems. Some systems use computers and other
advanced electronic equipment to solve navigational
problems automatically. The Aviation Electronics
communications and navigational equipment.
Several means of radio communications are in use
today. Some of these radio communications methods
intelligible coded radio-frequency waves as
! RadiotelephonyThe transmission of sound
intelligence (voice, music, or tones) by
continuous radio-frequency waves.
! RadiofacsimileThe transmission of still
images (weather maps, photographs, sketches,
and so forth) over a radio-frequency channel.
! RadioteletypeThe transmission of typewrit-
ten messages over a radio-frequency channel.
! RadiotelevisionThe transmission of a rapid
succession of images (still or moving) over a
Airborne communications equipment usually con-
sists of equipment that can use either or both radio-
telegraphy or radiotelephony. Radiotelegraphy and
radiotelephony are called Morse code and continuous
wave (CW) voice communications, respectively.
normally operate in a band of frequencies from about 3
MHz to 30 MHz. Frequencies within this band are
frequencies within this band have characteristics that
transmitted along the surface of the earth bend around
objects in its path. In addition, radio waves that are
transmitted skyward bounce off the ionosphere and
return to earth at extreme distances from the
transmitting station. This allows the waves to travel
extremely long distances.
Most long-range communications sets are designed
for both voice and CW (Morse code) operation. It is
often necessary to have a long antenna for long-range
communications. A weighted antenna wire (trailing
wire antenna) is installed in some large aircraft. The
wire is reeled out to provide an antenna of the desired
Short-range airborne communications sets operate
in the frequency range from about 30 MHz to 3 GHz.
very-high-frequency (VHF) band; the higher portion is
the ultra-high-frequency (UHF) band. The VHF/UHF
frequency bands have transmission characteristics that
differ from those frequencies in the HF band. Radio
waves transmitted at these frequencies travel in a
line-of-sight. VHF/UHF communications sets are
called line-of-sight communications sets. Radio waves
at these frequencies normally do not return to earth.
Therefore, VHF/UHF transceivers are mainly used for
air-to-air and air-to-ground contact in close range
operations. Landings and takeoffs are typical situations
using air-to-ground VHF/UHF transmissions.
munications. An example of this is the network of
remote-controlled transceivers installed along the
airways system in the United States. Pilots of aircraft
traveling the airways can talk directly to controllers in
distant aviation activities. A system of telephone lines
and relay stations connect the remote transceiver sites.
The radio part of the transmission takes place over a
relatively short distance.
Modern naval aircraft use a lot of navigational
equipment. Radio receivers and transmitters are used to
handle signals that determine bearing and/or distance.
The tactical air navigation (TACAN) system, Global
Positioning system (GPS), and navigation computer
systems are discussed briefly in the following