Functional Block Diagram Description of Receiver, Radio R-1467/GRC-144 Demodulator and Output Amplifier Circuits

TM 11-5820-695-35

limiter stages Q2 through Q5, discriminator driver

The output of emitter follower Q10 is a dc voltage which

stages Q6 and Q7, frequency discriminator T1, CR3 and

is inversely proportional to the age input to the de

CR4, and video output amplifier Q8 and Q9.

amplifier. The age input dc voltage increases as the

level of the 70 MHz if signal increases. This causes the

(1) The 70 MHz if signal from 2A5 is applied

agc dc output to decrease, proportionally, increasing the

through input amplifier Q1 (emitter follower) to the first

attenuation of diode attenuator circuits CR1 through

limiter stage Q2. The emitter follower matches the input

CR4 and decreasing the overall gain of 70 MHz if

impedance of the first limiter stage with the output

amplifier 2A5. The agc output of emitter follower Q10 is

impedance of 2A5.

also applied to Indicator, Antenna Alignment ID-

1708/GRC and agc metering circuits and to the if carrier

(2) Four limiter stages, Q2 through Q4,

monitor circuit.

remove amplitude variations in the 70 MHz signal.

Each limiter stage is operated as an overdriven

(3) The metering circuits provide agc signal

common base amplifier to clip the positive and negative

level outputs to the meter selector switch on meter

peaks of the 70 MHz if signal. A LIM TUNING control is

panel assembly 2A165A2 and to Indicator, Antenna

provided for tuning each limiter stage. The output of the

Alignment ID-1708/GRC. The agc output of peak

fourth limiter stage is applied to discriminator driver

detector CR5, CR6 is applied to the CARRIER (IF)

stages Q6 and Q7.

position of meter selector switch on meter panel

assembly 2A15A2 through meter circuit R32 and R37.

(3) Discriminator driver stages Q6 and Q7

The agc output of emitter follower Q10 is applied to the

consist of emitter follower Q6 and common base

AGC position of the meter selector switch (agc meter)

amplifier Q7. Emitter follower Q6 is used to match the

and to Indicator, Antenna Alignment ID-1708/GRC

output impedance of fourth limiter stage Q5 to the input

through meter circuit R84, R51, and R52. The reference

impedance of common base amplifier Q7. The output

(return lines) for the age metering and ant align ind

of discriminator driver stages Q6 and Q7 is applied to

outputs are applied through meter adjust circuit R46 and

frequency discriminator T1, CR3 and CR4.

R48. The METER ZERO control is used to set the

meter on 2A165A2 to electrical zero. To zero adjust the

(4) Frequency discriminator T1, CR8 and

meter, meter selector switch 2A15A2S1 must be set to

CR4 detects the frequency .variations in the 70 MHz if

the AGC position and the AGC SEL switch on 2A5 must

signal and converts the variations in the composite pcm

be set to the TEST position.

and orderwire signal. The DISCR PRIM control is used

to tune the primary winding of frequency discriminator

(4) The age output of emitter follower Q10 is

transformer T1.

The DISCR SEC control in the

also applied through monitor circuit R55 and R56 to

secondary of the frequency discriminator transformer T1

alarm monitor 2A12. The reference for the carrier (if)

is used to set the discriminator crossover frequency.

monitor signal is applied to alarm monitor 2A12 through

The composite pcm and orderwire output is applied to

carrier level alarm adjust circuit R60. Alarm monitor

1.0 MHz low pass filter 2A3 through video output

2A12 controls the CARR IF status indicator on meter

amplifier Q8 and Q9. Video output amplifier Q8 and Q9

panel assembly 2A15A2. If the carrier (if) monitor signal

amplifies the signals and isolates the frequency

is below a predetermined level, the CARR IF indicator

discriminator from 2A3.

lights green (normal indication). If the carrier (if)

monitor signal level rises above the predetermined

Low Pass Filter OAS. Low pass filter 2AS

level, the CARR IF indicator lights red (alarm condition).

The ALM SET control on 2A5 is used to set the level at

passes the composite pcm and orderwire signal to af-rf

which the alarm condition occurs.

amplifier 2A11. In the synchronous mode, the 1.0 MHz

low pass filter (684448) is used. In the asynchronous

mode, the 3.8 MHz low pass filter (684449) is used.

2-23.

Functional Block Diagram Description of

Both filters have a source impedance of 50 ohms and a

Receiver,

Radio

R-1467/GRC-144

load impedance of 150 ohms. The insertion loss of the

Demodulator and Output Amplifier Circuits

1.0 MHz filter is 0.5 dB maximum at 20 kHz. The

(fig. 5-19)

insertion loss of the 8.8 MHz filter is 0.3 dB maximum at

20 kHz.

Demodulator 2A4.

Demodulator 2A4

receives the 70 MHz if signal from 70 MHz if amplifier

AF-RF Amplifier 2A11. Af-rf amplifier

2A5 and converts the frequency deviations in the 70

MHz if signal into a composite pcm and orderwire

signal. The demodulator consists of input amplifier Q1,

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