Radio Frequency Oscillator O-l032/PRC-47 (A8A6)

TM 11-5820 -509-35

the output circuit to the load. For example, if the output

rectifiers CR26 through CR29 supply unfiltered 26.5

voltage of the regulator begins to rise, current through

volts dc at terminal P1-22. In addition, filtered +24 volts

the base-emitter circuit of Q2 will also increase. The

dc and regulated and filtered +20 volts dc are also

resulting voltage drop across resistor R19 lowers the

available from this circuit. During the transmit period,

potential at the base of Q 1 and reduces the conduction

push-to-talk relay K1 is energized by a ground placed on

current in this transistor. The decrease in collector-

the push-to-talk (ptt) key line (P1-11). As K1 contacts

emitter current flow in Q1 results in a corresponding

close, ac primary power is applied to terminals I and 5

decrease in conduction current in series regulator Q3.

on high-voltage transformer T1. Voltage step-up occurs

This reduces the output voltage of the regulator

in all secondary windings of this transformer except

terminals to near its steady-state value. The output

those identified by terminals 12, 13, and 14. This

voltage of the regulator is adjusted by setting

winding is used to power the vacuum-tube filament

potentiometer R22 while monitoring the output voltage

circuits and is a step-down winding. The rectifier filter

at tip jack J8.

circuits associated with the secondary windings of high-

voltage transformer T2 are conventional. The negative

potential furnished by bias rectifiers CR1 through CR4 is

2-13. Radio Frequency Oscillator O-l032/PRC-47

filtered by the resistance-capacitance network consisting

(A8A6) (fig. 7-13)

of R1-C1. The resulting output voltage is divided to

permit independent control of the-110-volt dc and the-

a. The temperature-compensated crystal oscillator

32-volt dc grid bias potentials required for operation of

circuit provides a highly accurate stabilized oscillator

power amplifier V101 and driver A3V3. Potentiometers

frequency of 3.000 MHz.

This circuit consists of

R3 and R4 provide moderate adjustment of these levels.

transistor Q1 in association with the crystal, inductor L1,

b. When a dc primary power source is connected

and voltage-controlled capacitor C12. Low values of

to the receiver-transmitter, P1-22 becomes +26.5 volts

crystal drive (approximately 10 microwatts) are

dc input for the low-voltage circuits. Transformer T2

maintained to enhance the long-term stability and to

remains deenergized with the dc power source

insure that the self-rectified voltage appearing across

connected, but filter C25-L1-C26 and the associated

C12 remains below the minimum required for

regulator network are used to provide +24 volts dc and

compensation over the entire operating temperature

regulated +20 volts dc to the connected circuits just as

range.

As the ambient temperature varies over

in the case of ac operation. The power oscillator circuit,

considerable limits, crystal frequency drift is maintained

located in the main chassis of the receiver-transmitter,

below 35 parts-per-million (ppm). Compensation for

operates as an inverter that provides a 26.5-volt

aging effects in the crystal circuit is provided for by

squarewave voltage to terminals 2 and 4 of high-voltage

variable capacitor C1. This device permits adjustment

transformer T2. Terminal 3 on this primary winding

of the output frequency by approximately +4 ppm. The

provides a convenient means for applying power to the

correction voltage supplied to voltage.

variable

power oscillator and the insertion of push-to-talk relay

capacitor C12 is derived from the temperature-sensitive

K1 contacts in this lead permits proper control during

network consisting of thermal resistors RT1 through

transmit periods.

RT3, and resistors R1 through R6, and R18. The effect

c. The filtered +24 volts dc from the low-voltage

of rapid ambient temperature changes on the output

power supply circuit is applied to the voltage regulator

frequency of the temperature-compensated crystal

input. Zener diode CR31 and resistor R20 provide a

oscillator is minimized by the encapsulation of the

reference voltage at the emitter of transistor Q2. The

crystal and its compensating network within a foam

base of this transistor samples the fluctations in output

insulating block. Amplifier Q2 and follower Q3 isolate

voltage that appear at the wiper of potentiometer R22,

the crystal oscillator circuit from variations in loading.

and these variations are amplified by Q1 and Q2 to

b. The 3.000-MHz output of the temperature-

provide a control bias that controls series regulator Q3.

compensated crystal oscillator is applied to a frequency

Variations in the bias applied to Q3 produce variations

divider circuit. Locked oscillator Q4 provides an output

in the collector-emitter current flow of this transistor, and

that is one-sixth of the input frequency but remains in

have an effect similar to the addition or removal of a

synchronism with this input signal.

The natural

series resistance in

frequency of locked oscillator Q4 is determined by the

network consisting of capacitors C13 through C16 in

2-28