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Fig. 12
Power feeding of the line repeaters. A power
looping adapter is placed after the last repeater
in the feeding chain.
Fig. 13
Regulation range for the two pilot regulated
equalizers 22372 kHz and 4287 kHz
determine whether there is any unbalance
because it is possible to measure
the voltage between each inner conductor
and earth. The circuit breaker for
the unit is key controlled, and it is thus
possible to prevent restarts, for example
during maintenance work.
Power feeding of the bay equipment
The units in the line terminating equipment
are combined to form a shelf
stack, those which are active being
power fed from two 12 Vd.c. converters
of 25 W each. One converter is used for
the units in the send direction and the
other for the units in the receive direction.
The 21 V d.c. converter of 30 W which
feeds the terminal repeater is also placed
in the shelf stack. The speaker circuit
shelf is provided with d.c. converters
of its own.
Level regulation
Level variations along the line are caused
by temperature changes in the cable.
The cable attenuation varies approximately
0.2 % per °C. The level variations
are mainly seasonal and are compensated
automatically by regulating line repeaters
along the line and, if necessary,
also by pilot regulated equalizers in the
receive side of the terminal equipment.
The main regulating pilot 61160 kHz is
active in the regulating line amplifiers
and the two extra pilots 22372 kHz and
4287 kHz are active only in their respective
equalizers.
The regulation range varies over the frequency
band, figs. 9 and 13. The range
is ±3 dB at each pilot frequency. Usually
it is sufficient to use single pilot regulation,
i.e. only the main pilot 61160
kHz, for the regulation of the system.
The use of two additional pilots, i.e. 3-
pilot regulation, is necessary only
when the cable is exposed to large temperature
variations or when the route is
very long. For example, when the route
contains an intermediate power feeding
repeater station between the two terminals
the use of 3-pilot regulation should
be considered.
It is sufficient to make every fourth line
repeater along the line regulating as
long as the variation in cable temperature
does not exceed ±10°C. If the variations
are greater than this, every third
or every second repeater must be regulating.
This situation arises when the
cable follows a bridge or a tunnel, since
it must then sometimes be run out in the
open, and is then exposed to rapid and
irregular temperature variations.
Equalization of the line
attenuation
When the system is put into operation
a curve is measured at the receiving terminal
which shows how the level deviates
from the expected value. This deviation
is caused by the differences in the
actual attenuation-frequency characteristic
of the cable in relation to what had
been anticipated. The resultant devia-
Fig. 11
Remote power feeding unit for feeding the line
repeaters