Selection and Testing of Electronic Components for LM

Fig. 5
ALBO network for automatic equalization of
0-25 dB (4.224 MHz) pair cable. The variable
resistance R is controlled by the peak amplitude
of the signal after the equalization
Vf+0.6f
characteristic
vT characteristic
Fig. 6
Strappable correction network and its frequency
characteristic
a) network configuration
b) attenuation
The network can be strapped to compensate for all cable
attenuations of the form Ad=\T+af where (K-a^-0.6
I.e. the cable parameters 3 can be selected independent
of each other
Fig. 4
Block diagram of the 8 Mbit/s digital repeater
and the associated signal diagram
Digital line repeaters for
ZAD8-2andZAD2-3
The function and block diagram for the
repeaters in ZAD 8-2 and ZAD 2-3
are similar and are shown in fig. 4.
However, in the case of the 8 Mbit/s
repeater the detailed design is more
comprehensive and requires more
space because of the more complicated
equalization conditions. Common tasks
for the two line repeaters are equalization,
timing recovery and pulse regeneration.
The purpose of the equalization is to
compensate for the frequency-dependent
attenuation introduced by the
cable. An optimum selection of attenuation/frequency
characteristic for the
equalizer means that the effect of disturbance
is minimized. The line repeaters
in ZAD 8-2 and ZAD 2-3 were dimensioned
with the aid of a computer,
and the goodness criterion was the
smallest possible signal/noise ratio at
the repeater input, i.e. maximum number
of disturbing systems for a given
bit error rate. For the purpose of dimensioning
it was assumed that the line
signal code was one of the internationally
standardized transmission codes,
HDB-3orAMI, and that the disturbances
had crosstalk characteristics. The effect
of thermal noise has been investigated
and has been found to have no significance
for the cable attenuations encountered
in ZAD 8-2. The maximum
cable attenuation that can be equalized
in the repeaters is 65 dB at 4.224 MHz
for ZAD 8-2 and 35 dB at 1.024 MHz
for ZAD 2-3.
The repeaters in the ZAD 8-2 system
each contain an equalizer consisting of
the following parts:
— a fixed part that equalizes the maximum
attenuation 65 dB of paperinsulated
pair cable with the attenuation/frequency
characteristic Vf~+
0.6 f.
— a fixed line building-out (LBO) network
which simulates a 15 dB cable
(at 4.224 MHz) and which can be connected
in for short repeater sections.
— a variable equalizer (ALBO) network
for 0-25 dB cable (at 4.224 MHz).
— a strappable network which can be
used to adapt the equalization to different
types of paper and polytheneinsulated
cable.
The configuration of the last two of
these networks are shown in figs. 5 and
6. This equalizer design means that line
equipment ZAD 8-2 can be adapted for
use with all pair and quad cables en-