Field Trial of Optical Fibre Cable-TV System Optical Fibre System for ...

Power
ZAV 280/4 has individual power supply
to each magazine. This ensures full
modularity at the magazine (evel anda
reasonable size of the knock-out unit in
the system. The maximum unit thuscorresponds
to four TV-channels.
The primary system voltage is -48Vd.c.
If this voltage is not available, rectifiers
are used which convert 220 V or 110V
a.c. to -48 V d.c. Uninterruptible power
can be arranged at -48 V if needed, but
consists of equipment separate from the
ZAV 280/4 system.
Fig. 14
ZAV 280/4 magazines in the Swedish Telecommunications
Administration's 19" cabinet. The
magazines are seen at the rear
Fig. 15
T/BYB rack for digital transmission equipment
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streams. If, on the other hand, the receiver
is in the wrong channel position
both output signals will be inverted, one
due to inversion on the send side and
the other one due to inversion on the
receiver side, so that the frame handler
cannot find any frame alignment word.
The controlling frame handler then
gives a change channel signal (CS) to
the receiver, which changes channel by
shifting the data by one bit slot in relation
to the clock.
In the short wave case the receiver preamplifier
consists of an avalanche photo
diode (APD) followed by an AGC-amplifier
(Automatic Gain Control) and equalizer.
The reverse voltage across the
APD, the gain and equalization are regulated
dynamically for optimal reception.
Timing recovery is done with a phaselocked
circuit containing, among other
items, a voltage controlled oscillator
(VCO). On start-up of the receiver it
sweeps the VCO frequency to phaselock
the receiver on the incoming timing
information from the received optical
signal. The timing circuit then controls
the sampling of incoming data.
After sampling, the regenerated
280 Mbit/s bit stream is demultiplexed
by clocking alternate bits to channels 1
and 2 respectively. If necessary, channel
switching is initiated as described
above.
The secondary system voltages are
±5 Vand ±15 V. These are generated by
d.c./d.c. converters in the magazines
Each magazine contains a d.c./d.c. converter
for ±5V (2x35 W) and one for
±15 V(2x15 W).
Construction practice
ZAV 280/4 is built in Ericsson's standard
construction practice BYB101. The
magazine are of type BFD 329 and are
19" wide, so that, with brackets, they can
be mounted in any standard 19" rack
system (fig. 14).
When the system is delivered with racks
from Ericsson, the new construction
practice for transmission equipment
T/BYB is used. T/BYB is a cost-optimized
further development of the MS
BYB construction practice.
Alarms
Each magazine in ZAV 280/4 contains an
alarm board. This printed board assembly
collects all alarms in the magazine
concentrates them into A and B alarms
and adapts the outputs to an external
standardized alarm interface using transistor
contacts.
The board is equipped with LEDsonthe
front which indicate A, B and P alarms
and there is also an outlet for system
alarm (SA). The system alarm can b'
connected to a separate LED module
which then identifies the faulty magazine.