Cable Digital Regenerator 1A12A13, Asynchronous Mode

TM 11-5820-695-35

the pcm is sliced into separate voltage pulses, logic

work, variable in increments which provide attenuation

ones, which represent the logic one bits in the pcm code

equivalent to one-quarter mile of cable, is provided to

as shown in figure 2-2, waveform B The output of slicer

terminate the line. This consists of three one-quarter

A1 is zero for logic zero bits The dc voltage developed

mile sections which can be selected by the operator.

by peak detector Q7/Q8 assures that the center of each

The section or sections selected modify the input signals

voltage pulse corresponds to the peak of the pcm signal.

to an equivalent that would be delivered by one mile of

The pcm signal, now designated ICSPCM, is sent to

cable.

cable control comparator 1A12A3 for retiming.

(2) The original FRCX signal from the source

(5) The 1CSPCM signal is integrated by Q9

end of the cable is comprised of a dc signal plus

which develops a dc output signal as long as logic one

squared voltage pulses representing the one bits in the

bits keep occurring at the input Lamp driver Q10 then

pcm modulation code. When the orderwire circuit is in

provides a ground output and lamp DS1 lights to

use, the orderwire audio signal is the third component of

indicate traffic activity. In the absence of traffic, lamp

the FRCX signal. This signal, at the input to 1A12A2, is

DS1 does not light and signal 1CRFAIL, which goes to

greatly degraded in quality after transmission through

alarm monitor 1A12A5, switches to logic one.

one mile of cable (or equivalent). A typical input FRCX

signal is illustrated in figure 2-2, waveform A.

a.1. Cable

Digital

Regenerator

1A12A13,

(3) The pcm portion of the input signal is

Asynchronous Mode (fig. 5-7.1 and 5-30.1)

coupled to the cable simulation networks and

transformer T1. Transformer T1 provides a voltage gain

(1) The discussion of the FRCX signal given in

of two. The dc is blocked from this path by capacitor C1

paragraph 2-5 all) and (2) applies also to the

and the orderwire is rejected by highpass filter C1/L7.

asynchronous mode. The FRCX signal is illustrated in

Overvoltage protection for following amplifiers is

figure 2-2. 1. At the input, the pcm component of the

provided by diodes CR1-CR4 which limit the maximum

composite FRCX signal is passed by high pass filter

amplitude of the input signal The orderwire and dc

C12-L7 and the dc and orderwire components are routed

signals go through low pass filter L1, L2 and L3 and are

into a second path through low pass filter L-7, L-10, L-

sent to chassis mounted transformer 1A12A15AlT1 as

11, R-9 s and C-35. The dc/orderwire signal, designated

the FRCX∅W signal

FRCXOW, is sent to chassis mounted transformer

1A12A12A1T1.

(4) The pcm signal at the secondary of

(2) In the pcm signal path, overvoltage

transformer T1 is degraded because of high frequency

protection for following circuits is provided by diodes

losses during cable transmission The pcm voltage

CR5 and CR6. The signal then passes from terminal (T)

pulses are no longer clearly defined and square and are

to terminal (N), (passing through the variable cable

low in amplitude Circuit Q1, of the 2304 kHz peaking

equalizer via terminals (L) and (Y), if it is in the circuit),

circuit, amplifies the pcm voltage pulses to provide a

and goes through the fixed cable equalizer. Variable

more sharply defined signal In the 2304 kHz peaking

resistor R6 adjusts the low frequency response of the

circuit, circuit Q1 is tuned to 2304 kHz which is the

equalizer

frequency used to time pcm voltage pulses for cable

transmission. Circuit Q2, with a voltage gain of 35, then

(3) At this point the signal is coupled through

greatly increases the sharpness and definition of the

capacitor C22 to emitter follower Q4, the traffic monitor

pcm voltage pulses The output of circuit Q2 is coupled

amplifier The output of Q4, designated XCPCM, is

through impedance matching emitter follower Q3 and

routed through a coaxial cable to alarm monitor

transformer T2 to amplifier Q5A Amplifier Q5A is a

1A12A15. Resistor R27 reduces the capacitive effect of

temperature compensated linear amplifier which further

the cable and prevents reflection of the signal back to

amplifies the signal Peak detector circuit A7/Q8 rectifies

Q4.

the pcm signal output of amplifier Q5A and develops a

filtered positive dc voltage across R40. The center arm

(4) An attenuator (resistors R12, R15 and R16)

of R40 is connected to the reference input of slicer Al.

at the input of linear amplifier A4 reduces the input

The pcm signal from Q5A also is connected to the other

signal to prevent overloading A4. The gain of linear

input of slicer A1. Slicer Al is a high speed differential

amplifier A4 is variable and is controlled by an agc

comparator. It produces a pulse output with a steep

signal developed in transistors Q1 and Q2 The output

vertical rise for positive voltage transitions of the input

signal of A4 Is coupled through a low pass

and a sharp vertical drop for negative transitions. Thus,

Change 2 2-12