cations, terrestrial, and satellite relay links, radar, and
special operations are some other uses.
Experimental use of the extremely-high-
frequency (ehf) band is ending. The Fleet Satellite
(FLTSAT) Ehf Package (FEP) is attached to two
modified uhf FLTSATs. The FEP is currently provid-
ing ehf communications capability to Army, Navy, and
Air Force ground, airborne, and oceangoing terminals.
We will discuss the FEP and its purpose in chapter 3.
Infrared devices and lasers use even higher fre-
quency ranges. Information on equipment using these
frequencies can be found in Electro-Optics, volume 9,
of this training series.
RADIO EMISSIONS
The emission class of an rf transmitter is deter-
mined by the type of modulation used. The interna-
tional designation system for AM and FM emissions is
shown in table 1-2. It designates the rf emission by
type, mode, and supplemental characteristics.
We will now discuss the basic equipment required
for communications.
TRANSMITTERS
For rf communications to take place, a signal has to
be generated. Generating the signal is the job of the
transmitter. The following paragraphs will very briefly
discuss basic transmitters and transmitter fundamen-
tals.
TRANSMITTER FUNDAMENTALS
Equipment used for generating, amplifying, and
transmitting an rf carrier is collectively called a radio
transmitter. Transmitters may be simple, low-power
units, for sending voice messages a short distance or
highly sophisticated, using thousands of watts of
power for sending many channels of data (voice, tele-
type, telemetry, t.v., etc.,) over long distances.
Basic transmitters are identified by their method of
modulation: continuous wave (CW), amplitude modu-
lation (AM), frequency modulation (FM), or single-
sideband (ssb). We will first describe the types of
modulation. We will then describe briefly the basic
transmitters themselves.
Table 1-2.—Types of Radio Emissions
MODULATION
Modulation is the process of varying some charac-
teristic of a periodic wave with an external signal. The
voice frequencies (about 110-3,000 Hz) are contained
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