Radio Control-Comparator 1A12A9 Circuit Functioning

TM 11-5820-695-35

Leading Edge Pulse Generator. Resistor

current flow through R39 must charge capacitor C15 to

+2 volts before the output of A8 switches to low. The

R29 and capacitor C8 form a delay circuit. The

time constant of R39, C15 is approximately 300

operation of this circuit is similar to that described for

milliseconds, so a delay of 300 milliseconds occurs after

delay circuit R39, C15 at the input of voltage

the output of A10 switches before A8 switches. If the

comparator 2 (e above).

output of A10 returns to logic zero (low) before the

output of A8 switches, capacitor C15 discharges and A8

Voltage Filtering Components.

Voltage

does not switch. This delay action bridges over intervals

filtering components L1 through L4 and C17 through

in the pcm signal when many consecutive zeros occur

C24 limit the coupling of switching transients and other

and prevents a false indication of failure when the pcm

stray signals to the power supply circuits.

signal is active.

2-48. Radio Control-Comparator 1A12A9 Circuit

Transition Detectors. Transition detectors 1

Functioning (fig 5-37)

(A9) and 2 (A10) are similar in circuit and operation to

alarm circuit 1 (A6) in cable digital processor 1A12A4

Radio control-comparator 1A12A9 contains integrated

(para 243b). The time constant for transition detector 1

circuits designated Al through A10.

Figure 5-24

(A9) is determined by R23 and C6 and is 350

provides a circuit diagram for each type of integrated

microseconds. The time constant for transition detector

circuit used. The circuits of 1A12A9 that are comprised

2 (A10) is determined by R38 and C14 and is 420

of discrete components are similar to corresponding

nanoseconds.

circuits of cable control comparator 1A12A3 and the

explanation of circuit operation is the same. Refer to

Slicers. Slicer 1 (A7) has a fixed reference

paragraph 242. The complete functional description of

voltage at pin 2, supplied by voltage divider resistors

radio control comparator 1A12A9 is provided in

R26 and R27. The supply voltages are filtered by C7

paragraph 2-6b.

and C25. Feedback through R28 improves circuit

stability. Resistor R25 isolates the input of A7 and

2-49. Radio Digital Processor 1A12A10 and 1A12A16

prevents feedback from the input circuit of A7 to the low

Circuit Theory (fig. 5-38 and 5-38.1)

impedance input of Q1A. When the input signal (pin 3)

is positive with respect to the reference signal (pin 2),

The integrated circuits used in radio digital processor

the output is low (logic zero). When the input signal is

1A12A10 and 1A12A16 are shown functionally in figure

negative with respect to the reference signal, the output

5-38 for the synchronous mode and in figure 538.1 for

is high (logic one). The reference voltage provided at

the asynchronous mode. Figures 538 and 538.1 specify

pin 3 of slicer 2 by resistors R32 and R35 is adjustable.

each integrated circuit type. Figure 5-24 provides a

It is filtered by C12. When the input signal (pin 2) of

circuit diagram for each type of integrated circuit used.

slicer 2 is positive with respect to the reference voltage

The complete functional description of radio digital

(pin 3), the output is high (logic one). When the input

processor 1A12A10 and 1A12A16 is provided in

signal is negative with respect to the reference voltage,

paragraph 2-6c and 2-6c.1. Electrical operation of

the output is low (logic zero).

discrete piece parts is provided below.

Tuned Circuit. When the output of inverter

Cable Output Amplifier. Transistor Q1 has a

Al is low, the voltage drop across R31 is 12 volts and

fixed dc bias, determined by voltage divider L1, R2 and

capacitor C10 charges to 12 volts through the primary of

CR1, at the emitter. The primary of transformer T1 is to

T1. When the output of Al switches to high (+5 volts),

collect load impedance. Resistor R3 is a current limiter

the voltage drop across R31 is reduced by 5 volts.

to protect Q1; R4 and CR2 clamp out inductive current

Capacitor C10 discharges through R31 and the

when the signal changes from logic one to logic zero.

transformer primary to the new voltage. The voltage

When the output signal at A4C is logic one, transistor

pulse produced by this discharge is coupled to the tuned

Q1 turns on and provides a current pulse through the

circuit in the transformer secondary. The secondary

primary of T1. This pulse is inductively coupled into

circuit is tuned to 2304 kHz by crystal Y1. Capacitor

both sections of the secondary.

Positive-going

C11 is used to null the stray capacitance of the crystal

transistion of the input signal is speeded up by the +5

circuit. As the tuned circuit oscillates, the voltage drop

volt source through resistor R39 and capacitor C1.

across R36 varies at the resonant frequency. The signal

is applied to A6 through current limiting resistor R37.

Change 2-87