AF-F Amplifier 1A4 Circuit Fun ctioning

TM 11-5820-695-35

A detected sample of the combined pcm

crystal mixer currents in mixer 1A16Z1 are also

and orderwire signal from radio transmitter modulator

provided. The CR1 metering and CR2 metering outputs

1A8 is applied to the traffic monitor attenuation circuit

are applied to the meter selector switch on the radio test

R15, R16 through section C2 of the selector switch and

set panel. Since the metering circuits are identical, only

pin 8. Resistor R15 and R16 provide the proper

the CR1 metering circuit is described.

Blocking,

attenuation before the signal is applied to alarm monitor

bypassing and filtering is accomplished by L5, C15,

1A5 through section C1 of the selector switch and pin 9.

C17, C19 and L7. These components prevent loading

With an input of 35 millivolts the traffic attenuator circuit

of the rf signal and also prevent rf from appearing at the

provides an output of 3.5 millivolts.

output. R15 and R17 comprise a voltage divider which

establishes the proper level for the meter. TP1 provides

a means to monitor the B + voltage (+ 15v). Resistor

2-31.

AF-F Amplifier 1A4 Circuit Fun ctioning (fig.

R1 is a dropping resistor and capacitor C2 provides rf

2-13)

bypass.

Af-rf amplifier 1A4 is a wideband video amplifier which

2-30.

Attenuator

Assembly

1A3

Circuit

provides a continuously adjustable gain (TRAFFIC

Functioning (figs. 2-12, 1-12.1 and 1-12.2)

LEVEL ADJ control).

The maximum gain of the

amplifier is 25 db. Af-rf amplifier 1A4 consists of first

video amplifier Q1, second video amplifier Q2, and

Attenuator assembly 1A3 consists of a

emitter follower Q3. The B + supply, + 15 vdc, input is

pcm attenuator/phase shift circuit, two (48 or 96

through P13. Three decoupling capacitors C2, 05, and

channel) orderwire attenuator/metering circuits, land two

C6, are used in the B+ circuit to remove ac ripple from

(48 or 96 channel) traffic monitor attenuation circuits.

the circuit. Test point TP1 (+ 15v) can be connected to

the meter selector switch with a test lead. Resistor R10

The pcm attenuator circuit consists of R1

is a metering resistor. Af-rf amplifier 1A4 is also used in

through R5, C1 and C2. Its input impedance is 50 ohms

position 2A11 of R-1467(P)/GRC-144(V)(refer to para 2-

resistive and its output impedance is 150 ohms. With

74).

an input signal of 350 millivolts at 5 kHz, the attenuator

provides an output signal of 5.3 millivolts. The circuit

1st Video Amplifier. The pcm signal from

also provides a pcm signal phase shift of 21 6 degrees

attenuator assembly 1: A3 is applied to input jack J1 IN.

at 300 Hz.

TRAFFIC LEVEL ADJ potentiometer R2 determines the

input level of the pcm signal coupled through C1 to the

The 48 CH/96 CH selector switch is set to

base of first video amplifier A1. The input impedance is

the 48 CH position to select the 48 channel

150 ohms (parallel combination of R1, R2, and input

attenuator/metering circuits for the orderwire signal.

impedance of first video amplifier Q1). Transistor Q1

The 96 CH selector switch position and associated

amplifies the pcm signal which is direct coupled to the

attenuator and metering circuits are provided for future

base of second video amplifier Q2. Resistor R17, in the

applications of Radio Set AN/ GRC-144. The orderwire

base circuit of Q1, stabilizes the input impedance of Q1.

input signal is applied across resistor network R6, R7

Resistor RX is the collector load for this stage and

and R8. OW LEVEL ADJUST control R8 is used to set

resistor R5 provides decoupling. Negative feedback is

the orderwire signal to the proper level for combining

utilized to reduce distortion. A feedback path is used

with the pcm signal in af-rf amplifier 1A4. The orderwire

from the emitter of Q3 (junction R9 and R15) to the

signal is then routed through section 01 of the selector

emitter circuit (R4) of Q1. A feedback path is also used

switch, resistor R9, and section C3 of the selector switch

from the emitter circuit (junction of R7 and R8) of Q2 to

to af-rf amplifier 1A4. The attenuator circuit has an

the base circuit (junction of R13 and C3) of Q1.

input impedance of 600 ohms and an output impedance

of 40 ohms. With an input of 780 millivolts at 1.0 kHz,

2nd Video Amplifier.

Second video

the attenuator circuit provides an output of 10.5

amplifier Q2 amplifies the pcm signal. The amplified

millivolts (adjustable by OW LEVEL ADJUST control).

output is direct coupled to the base of emitter

The orderwire signal is also coupled through C8 to the

metering circuit, detected by CR1, CR2, filtered by C4

and attenuated by R10, R11 for application to the meter

selector switch on meter panel assembly 1A15A8.

Variable resistor R10 is used to calibrate this metering

level.

Change 6

2-40