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TM 11-5895-1012-10
work depicted can be made up of all the types of tram
distances up to 6,000 miles. The ground distance be-
mission media described above. In addition, any one or
tween stations is dependent upon the equipment se-
all of the transmission links shown could have one or
lected and station design. A limitation on high fre-
mom intermediate relay or repeater stations as part of
quency radio is the small number of multiplexed chan-
the link, or span the distance without the need of these
nels which can be carried, usually 4 voice frequency
stations. The type of equipment selected and the make
up of the transmission link is determined by the dis-
(2) Line of sight Radio. These radio links operate
tance between breakout points, strategic and economic
in the very high frequency, ultra high frequency or mi-
factors, and the technical parameters required to pro-
crowave frequency regions. There must be 8 line of
vide the appropriate type and grade of service to the
sight path between the transmitting and receiving sta-
tions, however, this limitation is overshadowed by the
capability of such links carrying a high density of mul-
2-10. Communications Facilities
tiplexed communications channels.
(3) Tropospheric Scatter Radio. This type of
The communications facilities, which when connected
media relies on the forward scatter technique or propa-
together to form the worldwide common user system
gation. Tropospheric scatter can cover distances be-
can be classified as tributary stations, major relay sta-
tween 100 to 500 miles and carry a large number of
tions, or minor relay stations.
multiplexed channels, depending upon system design.
a. Tributary Stations. A tributary station provides
This media of transmission is also referred to as over-
communications services, telephone, teletype, data
the-horizon propagation and does not require a line-of-
etc., to activities located at the same base or installa-
eight path between stations.
tion. It is not a requirement that tributary stations be
(4) Satellite Radio. The distances covered by this
located on a base or installation. It could be positioned
media depends upon how high above the earth the
in a civilian community where there is a concentration
satellite relay station is positioned. The distance be-
of DCS users. The equipment installed at the tributary
tween earth stations usually vary between 2,000
station is compatible to that of the relay station or
and 6,000 miles. The transmission link is capable of
message switching center that provides access to the
carrying many multiplexed channels. The main limita-
DCS. In figure 2-2, the facilities located at Camp P
tion is that the channel capacity and position of the
and Camp J, are tributary stations located on the in
satellite relay station cannot be upgraded or changed.
stallation. From the tributary station, lines extend
(5) Metallic Links. Metallic links can be coaxial
outward to the user equipment. This equipment can be
cable, paired cable, or open wire. A metallic link can be
a single teletypewriter; banks of teletypewriters lo-
of all one type or by use of interfacing equipment be a
cated in the installation communications center; data
mixture of two or all three of the types. A metallic
terminals; a computer; a facsimile machine; and the in-
cable link can be either submarine or landline. Metallic
stallation telephone exchange. The telephone ex-
systems can carry a low density or a high density of
change further extends the service of the tributary sta-
multiplexed channels depending on the equipment and
tion to each authorized telephone user on the instal-
the type of cable selected and user requirements. The
lation. Stations PDQ and LMN are tributary stations
major limitation is in the construction of such systems.
not located on an installation, but in a town or city in
Right-of-way must be arranged and cable or wire laid
which there are a number of authorized users
to make the physical connection between the two
breakout points. An added factor is the maintenance,
requiring access to the DCS. The transmission link be-
and when needed, the repair of the outside plant facili-
tween the tributary station and its associated access
station to the DCS can be direct or require the use of
b. Transmission links utilizing line of sight paths,
repeater or a relay station.
b. Major and Minor Relay Station Tributary sta-
tropospheric scatter, and metallic media can cover the
required distance between breakout points directly or
tion access to the DCS is through a relay station,
may require intermediate stations to span the distance
Traffic flows through the access relay station onto the
between the two stations providing the breakout capa-
system to the distant tributary station. Relay stations
bility. These intermediate facilities are called relay
are classified as major or minor depending upon their`
stations for radio systems and repeater stations for
position in the DCS.
metallic systems. In either case the relay or repeater
(1) Major Relay Station. In figure 2-2, DCS
station performs the same function It will equalize
Station ABC can be classified as a major relay station.
and simplify the incoming signals to permit the re-
It is situated at a nodal (or junction) point of two or
transmission of a signal that, as near as possible, dupli-
more DCS subsystems. In addition to passing traffic
cates the original transmitted signal.
originating at or destined for a connected tributary
c. Referring to figure 2-1, the common user net-
station, it also acts as a circuit switching station. The

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