Communications Facilities

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

users.

capability of such links carrying a high density of mul-

2-10. Communications Facilities

tiplexed communications channels.

(fig. 2-2)

(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

ties.

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

2-6