Second Oscillator

TM 11-5820-549-50-1

The transistor for the limiter is contained in the detector

Z2- 4 is developed across a capacitively coupled

integrated circuit Z5. The 455 kHz i.f. signal is applied

double-tuned circuit consisting of C18, T5, C19, C20

to the limiter input at Z5-3 by the capacitor C29. The

and T6. The signal is then transferred at a reduced

output of the limiter from Z5-1 passing through the

impedance from the tap on T6 by means of C21 to the

isolation resistor R2 drives the discriminator input tuned

input of the second mixer at Z25. Capacitor C22

circuit, C30 and T7, by means of a top on T7. The

functions as the signal bypass for the amplifier.

secondary winding of T7 acts as a tickler for the

discriminator secondary T8.

The discriminator

1-9. Second Oscillator

secondary tuning capacitors, detection diodes and a

low-pass filter are contained in electronic component

The transistor for the second oscillator is contained in

assembly Z3. The low-pass filter has two isolated

the .i.f. integrated circuit Z2. The second oscillator

outputs, one, Z3-2, applying signal to the squelch control

operating at 10.245 MHz is a Pierce type with the crystal

R5 and the other, Z3-1, applying signal to the volume

Y2 operating at its fundamental parallel resonant mode.

control R7. Capacitor C36 is the signal bypass for the

The leads of crystal (type CR-64U) are soldered to the

limiter. The B+ filter network C22, L6 and C36 provide

circuit board. Capacitors C24 and C25 form the phase-

isolation between the 455 kHz i.f. amplifier and the

reversing voltage divider for the feedback signal from

limiter.

collector, Z2-1, to ground and from base, Z2-2 to

ground. Capacitor C23 couples the 10.245 MHz signal

1-13. Audio Circuit

to the input of the second mixer at Z2-5. Capacitor C22

is the signal bypass for the circuit.

The recovered fm modulation (voice or tone) is applied

across the volume control R7. The desired level of the

1-10. Second Mixer and 455 KHz Filter

signal is selected by the adjustment of R7 and is

coupled to the input of the audio amplifier at Z5-13 by

The transistor for the second mixer is contained in the

capacitor C40. The audio amplifier is contained in the

i.f. integrated circuit Z2. Both the 10.7 MHz i.f. signal

detector integrated circuit Z5. The output signal is

and the 10.245 MHz oscillator signal are coupled to the

applied from Z5-10 to the horn transducer LS1 or the

input of the second mixer Z2-5, at the junction of C21

headset H-302(XE-1)/PRR-9 by means of the earphone

and C23. The desired difference frequency signal of

jack J5. Both the horn and the headset have an

455 kHz is developed across the input of the ceramic

impedance of approximately 220 ohms and a resistance

ladder filter FL1. The filter has a -6 decibel (db)

of 80 ohms. Capacitors C40 and C42 are instrumental

bandwidth of approximately 40 kHz and a -60 db

in determining the low frequency roll-off. Capacitor C43

bandwidth of approximately 70 kHz. Capacitor C22 is

assures stability of the audio amplifier by minimizing

the signal bypass for the second mixer.

gain at frequencies above the audio spectrum. The

signal bypass for the audio amplifier B + line is capacitor

1-11. I.f. Amplifier, 455 KHz

C36. Diode CR3, in series with J5, allows the horn

transducer LS1 to function in the event J5 short circuits

Three cascaded stages of 455 kHz gain are contained in

to ground (B-).

the i.f. integrated circuit Z2. The input signal for the

first stage is taken from the output of the ladder filter

1-14. Tone Squelch Circuit

FL1 and is introduced at Z1-8 to the amplifier.

Capacitor C26 provides coupling between the first and

second stages of gain from Z2-9 to Z2-10. Capacitor

a. Tone squelch (150 Hz) is activated when the

C28 couples the signal from the second to the third

receiver control is initially turned on. Squelch switch S1,

stage of gain from Z2-11 to Z2-12. Capacitor C29

which is a part of the receiver control, is open in this

couples the signal from the output of the third stage at

condition. The audio amplifier is disabled and dissipates

Z2-13 to the input of the limiter at Z54. The signal

no power in the absence of signal. Upon reception of a

bypass for the B + line is C22.

signal with 250 Hz sidetone modulation, the 150 Hz

signal is applied across the squelch adjust potentiometer

1-12. Limiter and Discriminator

R5. The proper level of signal is coupled from R5 by

capacitor C35 through R3 to the input of the squelch

circuit at Z5-4. The. transistor for

1-3