Digital Data Modem 1A12 Radio-to-Cable Circuits Functional Block

TM 11-5820-695-35

Radio R-1467/C-144; separates the pcm signal from the

(9) Under normal operating conditions,

orderwire signal; reshapes and amplifies this signal and

the signals at U5D-12 and U5C-9 and -10 are logic 0,

applies output signals to 1A12A7 and 1A12A9

and the signal at U5D-13 is logic 1. U5D-11 and U5C-8

(1RSPCM-1 and 1RSPCM-2).

then apply logic 1 at U1B-4 and U1A-2, respectively.

When signals DATA (TO RADIO) at U9B-10 and DATA

(1)

Pcm recovery circuits.

(TO DGM) at U9A-2 are active, the signals at U9B-12

and U9A-4 are logic 0. U1C-8 then applies logic 0 at

U1B-5 and U9A-4 applies logic 0 at U1A-1. U1B-6 and

(a) Signal FRPCM is applied to

U1A-3 are then logic 0, signals TR FAIL and DT FAIL

differential amplifier Q1A, B which generates a signal

are logic 0 (normal), and status indicator CR3 is off. If

proportional to the difference between the input signal

the DATA (TO RADIO) signal fails, U9B times out and

and a fixed reference. Linear buffer 1 (Q2, Q3)

resets, and U9B-12 applies logic 1 at U1C-9. The

provides a signal with a low impedance source to drive

0HIBTR signal at U11C-10 is normally logic 1 (see chart

the following peak detectors.

The peak detectors

in para (5) above) so U1C-8 applies, logic 1 at U1B-5.

consist of two half-wave diode rectifiers and filter

Since the signal at U1B-4 is normally logic 1, the signal

circuits. The time constants of the filter circuits allow

at U1B-6 changes to logic 1 and signal TR FAIL is in the

the capacitors to charge to the positive and negative

fault state. The logic 1 from U1B-6 changes the signal

peak excursions of the input signal.

at U8B-4 to logic 0 and indicator CR3 turns on. In a

similar manner, failure of the DATA (TO DGM) signal

(b) The detected signals are

changes the DT FAIL signal to logic 1 (fault) and lights

applied to a voltage divider which derives the algebraic

indicator CR3. U50 has two logic 1 inputs and logic 0

average of the peak-detected voltages. Linear buffers 2

output (U5D-11) only when signal DGMDEF is logic 1

and 3 (Q4 and Q5) provide a high impedance buffer

(fault) and LOOP TEST switch is not in RADIO position.

between the peak detector circuits and the input of

For this condition, U1B is inhibited and a TR FAIL fault

voltage comparator A4.

Voltage comparator A4

indication cannot occur. U5C has two logic 1 inputs only

compares the inputs from linear buffers 2 and 3. The

when signal DGMDEF is logic 1 (fault) and LOOP TEST

output of linear buffer 3 (Q4B, Q5B) is the reference

switch is in DGM position. For this condition, U1A

signal for the voltage comparator. When the amplified

inhibits a DT FAIL fault indication.

FRPCM output of linear buffer 2 (Q4A, Q5A) is more

positive than the reference, the voltage comparator

output is high; when the amplified FRPCM signal is

2-6. Digital Data Modem 1A12 Radio-to-Cable

more negative than the reference, the voltage

Circuits Functional Block (fig. 5-8 and 5-8.1)

comparator output is low. The output signal from the

voltage comparator is the reshaped pcm signal.

The functional relationships between the radio-to-cable

plug-in components and chassis circuits in digital data

modem 1A12 are shown in figure 5-8 for the

output (pcm signal) of the voltage comparator for

synchronous mode and in figure 5-8.1 for the

application to digital buffers A3B and A3C. These

asynchronous mode.

Each plug-in component is

reinvert the signal and provide parallel outputs

functionalized and the main signal paths (heavy lines

(1RSPCM-1) and 1RSPCM-2).

through each plug-in component and between plug-in

components) are shown. In addition, the control and

(d) The output signal of digital

alarm functions are shown. The operation of the

buffer A3C (1RSPCM-2) is also connected to transition

synchronous mode plug-in components is described in a

detector 1 (A9) which is a monostable multivibrator.

through h and the operation of the asynchronous plug-in

Each time monostable multivibrator A9 is triggered by

components is described in b.1, c.1, and i.

the negative-going transition of a logic one and holds for

350 microseconds (approximately). If A9 receives

Radio Digital Regenerator 1A12A8 (fig. 5-8

another trigger

and 5-36). Radio digital regenerator 1A12A8 receives

the pcm plus orderwire signal (FRPCM) from Receiver,

Change 6 2-16.14