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The four-wire circuit permits a long speaker circuit connection without
stability problems, which is a general requirement.
The terminal repeaters also contain the necessary hybrid for directly
connecting to various two-wire trunks in the repeater station.
A. c. signalling is used on the two-wire side.
Mechanics
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Terminal Repeaters
The terminal repeater—containing high frequency equipment, power supply
equipment, fault locating and alarm equipment, and speaker circuit equipment—is
made up of plug-in, electrical and mechanical functional units
mounted on a single-sided bay according to L M Ericsson's standard principles
as described in Ericsson Review No. 4, 1960. The exception is the units which
contain send and receive line amplifiers, which are constructed on the
principles described below for repeater amplifiers. This was done in order to
avoid variant types of equipment, with the trouble which this involves in
spare parts stocks. The lower part of the bay is therefore slightly differently
arranged in order to provide space for these line amplifier units.
Fig. 9 shows a terminal repeater bay for the 1.3 Mc/s system. At the top is
the distribution frame which allows convenient connection of the bay equipment
to the station cable. Thereafter follow power pack and remote power
feeding unit. In the middle of the bay is the fault locating and speaker
circuit equipment, surrounded by the high frequency equipment. The lower
part of the bay accommodates send and receive line amplifiers. All maintenance
test points are shortcircuitproof and placed on the sides of the bay.
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The bay accommodates two complete h. f. line equipments containing all
the above-mentioned auxiliary equipments.
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Used as a power-feeding intermediate repeater, the capacity is reduced to
one system per bay.
Intermediate Repeaters
The intermediate dependent repeater stations must be of a type which can
be buried. Arrangements should, however, exist for easy access to the line
amplifier equipment so as to cut down the time taken to replace a faulty unit
to acceptable limits. The replaceable equipment should consist of hermetically
sealed units which are insensitive to moisture. This is of vital significance for
preventing unnecessary disturbances of operation on account of moisture
damage. The units must be so placed as to eliminate the risk of freezing in
the soil in wintertime.
For human safety all accessible equipment should be at earth potential.
Fig. 9
It is also desirable that the coaxial tubes of the main cable terminate on a
Terminal repeater bay for 1.3 Mc s system ...... , • . , , , • • , , T-U ovist
distribution frame into which the repeater equipment is plugged. The coaxiai
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