100 MHz Radio Frequency Oscillator 1A2 Circuit Functioning

TM 11-5820-695-35

transistor Q1, crystal Y1, and tank circuit L3, C7, C10.

(3) Oscillations and noise in the high gain

Crystal Y1 operates in series resonance on the fifth

feedback regulator are prevented by C2 and C3.

overtone. Transistor bias is provided by resistors R3,

Capacitor C2 shunts any disturbances at Q2 base to

R4 and R5. Resistor R5 is also in the oscillator's

ground. Capacitor C3 supplies negative feedback to the

feedback path. Inductor L4 tunes out stray capacitance

base of Q6 to prevent oscillations. Capacitor C4

in the crystal unit. Capacitor C6 provides rf bypass. Dc

suppresses any noise which otherwise could trigger Q1

power is applied through switch S1, and two filter

during normal operating conditions. Diodes CR5 and

sections (L1, C1, C3 and L2, C4, C5). The switch also

CR7 are temperature compensating diodes in the base

controls the RADIO TEST SET lamp on meter panel

circuits of Q7 and Q9.

assembly 1A15A8 and on-off lamp DS1 on the front

panel of 1A2 through current dropping resistor R2.

12v Voltage Regulator 1A1A6 through

1A1A9 (fig. 2-10). This circuit functions the same as the

When voltage is applied, the initial

6/6v voltage regulator previously described in a above.

transient causes oscillations to start. Crystal oscillations

The difference between the circuits is that 6.2-volt zener

are fed through C21 and R5 to the emitter of Q1,

diode references are used (CR5 and CR6) in place of

amplified in the transistor, and applied to the tank

the 3.3-volt type (CR6 and CR8) used in the 5/6v

circuit. The tank circuit, closely tuned to the crystal

voltage regulator. Only one potentiometer (R4) is

frequency, resonates and feeds a reinforcing signal

provided in the voltage divider path (R4 and R6) and the

through C8. The signal builds up in the loop until the

temperature compensating diodes in the base circuits of

transistor gain has decreased to unity, at which point a

Q7 and Q9 are not used. Also, capacitor-resistor

sustained level is maintained. Small changes are made

network Z1 is used in the base circuit of Q6 to eliminate

in operating frequency by means of variable capacitor

possible oscillations under a low load condition. An

C10 in the tank circuit. When the tank circuit is tuned to

identical 12v voltage regulator is used in position 2A1A3

resonate above the natural frequency of the crystal, the

of Receiver, Radio R-1467/GRC-1144.

feedback signal to the crystal leads the crystal signal.

This causes the crystal to oscillate at a higher frequency

15/28v Voltage Regulator 1AA10 through

and restores a zero phase condition. Since the crystal

1A1A12 (fig. 2-11). This circuit functions the same as

Q is very high, compared to that of the tank, the change

the 5/6v voltage regulator previously described in a

in crystal frequency required to restore zero phase is

above. The difference between the circuits is that 6.2-

very small relative to the change in resonant frequency

volt zener diode references are used (CR-5 and CR6) in

in the tank circuit. The oscillator output is taken off at

place of the 3.3-volt type (CR6 and CR8) used in the

the upper tap of L3, through coupling capacitor C9. The

5/6v voltage regulator. Also, certain circuit resistance

signal is fed to a power splitter (R10 through R14) which

values are different to accommodate the higher voltages

also isolates the oscillator from the load. Each output is

and the temperature compensating diodes in the base

coupled by blocking capacitors C13 and C14 to the

circuits of Q7 and Q9 are not used. In addition, resistor

output cables W1 and W2. These cables are connected

R16 is required to limit the crowbar current and

to balanced mixer unit 1Z1. The blocking capacitors

capacitor-resistor network Z1 is used in the base circuit

prevent diode currents in the mixer from feeding back to

of Q6 to eliminate possible oscillations under a low load

the oscillator stage.

condition. Identical 15/28v voltage regulators are used

in positions 2A1A1, 2A1A2, and 2A1A4 of Receiver,

Several metering circuits are provided. A

Radio R-1467/GRC-144.

diode detector circuit, consisting of CR1, R8, R0 is

capacitively coupled by C11 to the variable arm of R7

2-29.

100 MHz Radio Frequency Oscillator 1A2

(LEVEL ADJ).

This circuit produces a dc level

Circuit Functioning (fig. 5-23)

proportional to the signal level. The dc level (osc output

level) is applied to the meter selector switch on the radio

The 100 MHz radio frequency oscillator

test set panel. Potentiometer R9 (cal adj 4th-5th ech

1A2, functionally part of the radio test set, produces a

only) is used to adjust the meter deflection and capacitor

precise 100 MHz signal, which is mixed with the output

C12 is an rf bypass. Circuits for metering the

signal of the T-1054/GRC-144 to produce a signal offset

by 100 MHz from the rf output frequency. The signal is

used in aligning, testing, and troubleshooting the R-

1467/GRC-144.

The basic oscillator consists of

Change 5

2-57