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Fig. 6
Oscillogram of transient response of line
regulating equipment for a section consisting
of 26 intermediate repeater stations
Ordinate: 0.06 db per division
Abscissa: 0.2 second per division
The principle of using a pilot receiver in each intermediate repeater also
means that the supervision of the intermediate repeaters can be based on
testing of the outgoing pilot level. This permits the simplest and most reliable
method of fault tracing. The regulators, which are of proportional type, are
accurately designed in respect of envelope gain, and therefore no stability
problems arise even on long pilot sections (several regulators in cascade).
Fig. 6 shows an oscillogram of the transient response of the line regulating
equipment over a distance comprising 26 intermediate repeaters when the
transmitted pilot level is changed in steps of 1 db. Note the short regulating
time and that no overshoot occurs.
A simplified circuit diagram of a repeater with associated regulator is
shown in fig. 7.
The repeater equipment has been designed for very high reliability.
Miniaturization has therefore not been taken too far. The number of components
has been kept as low as possible, and only silicon-planar transistors
have been used.
The function of the terminal repater on the left in fig. 4 is, on the send
side, to handle the band from the modulating equipment, adding the pilots
required for the h. f. line and producing the desired output level characteristic.
On the receive side the equipment restores the frequency band from the cable
to a flat level curve and filters out the line pilots. The receive side also
contains an equalizing equipment, the function of which is to eliminate the
inevitable variation of equivalent of the h. f. line. This variation may suitably
be divided into a fixed portion and a portion which varies with time, each
being treated separately in the equalizing equipment. The fixed portion is
caused by systematic addition of inevitable small deviations in each intermediate
repeater from the ideal gain curve. By means of advanced calculation
and manufacturing technique it has been possible to reduce these deviations
to very small values, but despite this great accuracy it is necessary to insert an
equalizing network after some 20 intermediate repeaters.
The portion which varies with time is caused in the same way by systematic
addition of small deviations of the regulation characteristic of the repeaters
from the ideal and is eliminated by means of a simple manually adjustable
network. Manual adjustment was adopted since the variations take place very
slowly; they are a function of the variation of the cable temperature according
to the season of the year. The temperature dependence of the repeaters themselves
is negligible.
Fig. 7
Simplified
circuit diagram for
1 Power separation Alter
2 Gain equalizer
3 Amplifier
4 Pilot receiver
5 Pilot alarm
6 Test point
line amplifier
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