SERVO AMPLIFIER DISABLE

TO 31R2-2GRC171-2

TM 11-5820-815-14

NAVELEX 0967-LP-544-5010

Q17, Q16, and Q23 amplify the negative output voltage

from U8 to control base drive to transistor Q20.

voltage. which would be the case if the d/a analog signal

Transistor Q23 also provides base drive through re-

tries to drive the rf filter above 400 MHz, or if the rf filter

sistor R92 to the up frequency enable transistor, Q19,

actually is driven above 400 MHz, the output of U9A

causing it to turn on. Transistor Q20, when turned on,

goes positive to turn on transistor Q24. When on, Q24

provides' voltage to the servo motor (positive voltage to

shunts to ground base drive to transistor Q19. This turns

P1-22). Transistor Q19 provides a ground return for the

Q19 off which opens the motor circuit to prevent the rf

servo motor (P1-Z). Servo amplifier gain maintains

filter from being driven any higher in frequency. In a

approximately 13 V dc across the servo motor to drive

similar manner, if the resulting voltage exceeds the lower

the rf filter toward the higher frequency. As the new

limit voltage, which would be the case if the d/a analog

frequency is approached, the output of U8 goes toward 0

signal tries to drive the rf filter below 225 MHz or if the rf

volt which in turn reduces the base drive to transistors

filter is actually driven below 225 MHz, the output of U9B

Q20 and Q19. At the null, transistors Q20 and Q19 turn

goes negative to turn on transistor Q25. When on, Q25

off to stop the rf filter at the new frequency.

shunts to ground base drive to transistor Q21. This turns

Q21 off which opens the motor circuit to prevent the rf

4-56. When the radio control is set to a lower fre-

filter from being driven any lower in frequency. Through

quency, the d/a analog voltage at the non-inverting input

this circuit action, the rf filter is prevented from being

of U7 becomes negative with respect to the position

driven above 400 MHz (upper end stop) or below 225

feedback voltage at the inverting input of U7. This

MHz (lower end stop).

results in a negative servo error signal to the inverting

input of the servo error amplifier, U8. The resulting

4-58. SERVO FAULT AMPLIFIER. The servo fault

positive output voltage from U8 reverse biases

amplifier (Q14 of figure FO-18) receives inputs from the

transistors Q17 of the up frequency servo drive circuit

servo amplifier through diodes CR17 and CR18 and from

(Q17, Q16, Q23, Q20) and forward biases transistor Q15

the 200- to 219-MHz decoder (U5) through diode CR32

of the down frequency servo drive circuit (Q15. Q22,

and provides at its output a dual-purpose rf filter fault

Q18). When Q15 is forward biased, transistors Q15 and

signal. The fault signal goes to logic 0 to indicate an

Q22 amplify the positive output voltage from U8 to

invalid circuit condition if the radio control frequency is

control base drive to transistor Q18. Transistor Q22 also

set below 220 MHz or if a servo malfunction causes

provides base drive through resistor R101 to the down

voltage to be applied to the servo motor at times other

frequency enable transistor, Q21, causing it to turn on.

than normal tuning. For normal servo operation, the rf

Transistor Q18, when turned on, provides voltage to the

filter fault signal goes to logic 0 to provide a tune-in-

servo motor (positive voltage to P1-Z). Transistor Q21

progress indication whenever the rf filter is in the process

provides a ground return for the servo motor (P1-22).

of being tuned.

The applied voltage to the servo motor drives the rf filter

toward the lower frequency. As the new frequency is

4-59. The circuit operates as follows. Whenever the

approached, the output of U8 goes toward 0 volt which in

radio control frequency is set below 220 MHz, all inputs

turn reduces the base drive to transistors Q18 and Q21.

to the 200- to 219-MHz decoder, U5, become logic 0.

At the null, transistors Q18 and Q21 turn off to stop the rf

This results in a logic 1 output voltage that is applied

filter at the new frequency.

through diode CR32 to the base of servo fault amplifier

transistor Q14 causing it to turn on. When Q14 turns on,

4-57. SERVO AMPLIFIERDISABLE. The servo amp-

the rf filter fault output (P1-3) goes to logic 0 to indicate

lifier disable circuit (U9A, U9B, Q24, Q25 of figure FO-

an invalid circuit condition. If the radio control frequency

18) functions as a double ended limit detector to turn off

is set at 220 MHz or above, the rf filter fault output goes

the servo motor if it tries to run past the end stops of the

to logic 0 whenever the voltage applied to the servo

servo mechanism. Resistor R106 of voltage divider

motor exceeds a threshold (about 7.5 V dc) established

R108-R106-R105 is test selected to set the upper limit

through voltage divider action of diode CR17 or CR18,

voltage applied to the inverting input of U9A

zener diode VR1, and resistors R60, R59, and R61.

(approximately +4.1 V dc). Resistor R107 of voltage

Servo motor voltages greater than the threshold develop

divider R109-R107-R68 is test selected to set the lower

sufficient voltage across R61 to forward bias transistor

limit voltage applied to the inverting input of U9B

Q14 and turn it on. Capacitor C10 and resistors R59 and

(approximately -4.1 V dc). The position feedback signal

R61 form a slow release circuit to hold the filter fault

is applied to the non-inverting inputs of both U9A and

output at logic 0 f or at least 10 milliseconds after the

U9B. Also, the d/a analog signal is applied through

servo motor voltage decreases below the threshold.

resistor R70 to the non-inverting inputs. If the resulting

voltage from these two signals is between the upper and

4-60.

FREQUENCY SYNTHESIZER MODULE A2.

lower limit voltage, the output of U9A will be negative to

turn off transistor Q24 and the output of U9B will be

4-61. GENERAL. Frequency synthesizer module A2

positive to turn off transistor Q25. If the resulting voltage

utilizes a 2-modulus prescaler form of digital phase-lock

exceeds the upper limit

loop (p11) to generate the transmit frequency to

4-10