Electronic Frequency Control 1A7 Circuit Functioning

TM 11-582069535

conjunction with resistor R33 provides a regulated minus

coupled in pin 2 to the noninverting input pin 3 of

8.2 volts.

operational amplifier AR3 (fig. 2-14(3)) and through

R25 and pin 4 to the meter selector switch on meter

panel assembly 1A15A8. Resistors R26, R27 and R28

2-33.

4.5 MHz Low Pass Filter 1A6

in the signal input path form a pad that provides

Circuit Functioning

approximately 15 db of attenuation. The amplified

(fig. 2-15)

output from operational amplifier AR3 is connected by a

jumper between terminal E54 and terminal E55 to the

The 4.5 MHz low pass filter is connected in the

base of transistor QL1 (fig. 2-14(2)). Transistors Q11

orderwire/pcm signal path between af-rf amplifier 1A4

and Q12 form a Schmitt trigger circuit that functions in a

and radio transmitter modulator LA8. It aids in the

similar manner to Q5 and Q6 previously described in b

overall shaping of the pulses before frequency

above. When the rf power is above a minimum treshold

modulation. The filter is a five-pole low pass filter and is

level, established by the setting of the input attenuator,

tuned to approximate Gaussian shaping and has a

output transistor Q13 is conducting and provides a low

nominal 3dB bandwidth of 4.5 MHz. At 6.4, 9.1, and

impedance ground path for the normal indicator. When

12.5 MHz the filter attenuation is 6, 12, and 20 dB,

no signal is present, transistor Q12 is conducting and

respectively. Source impedance is 50 ohms and load

provides a low impedance ground path for the alarm

impedance is 150 ohms. The filtering components are

indicator.

L1, L2, and C1 through C5 and resistor R1 provides

impedance matching.

For Transmitter, Radio T-

A synthesizer monitor signal is developed in

1054(P)A/GC-144(V) , low pass 'filter 1A6 is not used for

electrical frequency synthesizer 1A14 and applied

data rates 9 and 18 MB/s; it is replaced by cable

transistor to Q14 through pin P2-17 (fig. 2-14 (2). This

assembly 1A6W1.

signal indicates when electrical frequency synthesizer

1'A14 is not phase locked and is in a search mode

2-34.

Electronic Frequency Control 1A7

attempting to correct the oscillator frequency. The

Circuit Functioning

Schmitt trigger consists of transistors Q14 and Q16.

(fig. 5-25)

When electrical frequency synthesizer 1A14 is phase-

locked, a +2 volt level is applied to input pin 17 to

Electronic frequency control 1A7 produces an afc signal

forward bias transistor Q14. This in turn, cuts off

which stabilizes the center frequency of the 150 MHz

transistor Q15 and turns on transistor Q16 providing the

vco in radio transmitter modulator 1A8. Electronic

normal (green) indication. When electrical frequency

frequency control LA7 is comprised of the following

synthesizer 1A14 is not phase locked, the input signal

circuits: (1) 70 MHz frequency modulated input, (2)

drops to zero volts which turns on transistor Q15

reference crystal oscillator, (3) multivibrator, (4)

producing the alarm (red) indication.

amplifier-limiter chain, (6) discriminator, (6) ac amplifier,

and (7) phase detector.

A four-input diode OR gate and inverting

transistor provides the summary alarm function. This

70 MHz Frequency Modulated Input Circuit.

circuit consists of diodes CR12 through CR15, transistor

The 70 MHz frequency modulated signal (FREQ CONT

Q23, and resistors R102 and R103 (fig. 2-14(2)). When

INTERCONN) from 1AS is applied to emitter follower

the anode of any input has a positive voltage level

Q3 via coupling capacitor C5 and connector J'1 (IN-

applied to it, it conducts and forward biases transistor

PUT). This stage isolates the input from the load.

Q23 into conduction producing a summary alarm

Resistor R8, which is rf grounded by capacitor C9,

condition. When all of the diodes have a low (or zem)

provides the proper termination at the input. The stage

voltage applied to their anodes, they are nonconducting

is biased by resistors R9, RIO, and R26. The output

and transistor Q23 is turned off producing a normal

from R11 is fed to a diode gate through C14.

indication.

Capacitors C27 and C30 provide bypass and L9 is an rf

choke. The diode gate consists of CR4,

Two zener diodes are incorporated on board

1A1, these provide regulated positive and negative

voltages for the integrated circuits (fig. 2 14(3)). Zener

diode CR5 in conjunction with resistor R31 provides a

regulated plus 10 volts.

Zener diode CR6, in

2-66

Change 6