Antenna and rf Circuits

TM 11-5820-549-50-1

c. Capacitors C4 and C5 provide signal bypassing

c. The output of the first mixer is then applied to a

of the T2 secondary.

10.7 MHz i.f. amplifier where the signal is amplified and

applied to the input of the second mixer. The output of

d. Rf choke L2, in conjunction with the capacitors

the second oscillator, which is crystal-controlled by a

C6 and C9, form a B+ decoupling network providing

10.245 MHz crystal, is also applied to the second mixer.

isolation between the rf amplifier and the first mixer.

The mixing of the 10.'7 MHz and 10.245 MHz signal

results in an output signal of 455 kilohertz (kHz).

1-6. Local Oscillator

d. The output of the second mixer is coupled

through a 455 kHz i.f. filter, which establishes the major

The transistor for the local oscillator is contained in

bandpass characteristics of the receiver. The 455 kHz

integrated circuit Z1. A third overtone (CR-81/U) crystal

signal is then amplified by the 455 kHz i.f. amplifier and

(Y1) operating in the series-resonant mode de" -mines

applied to the limiter.

the frequency of oscillation 10.7 MHz below the

incoming rf signal. The oscillator output tuned circuit

e. Proper limiting of the fm signal is accomplished

consists of a piston trimmer, C15, and a fixed shielded

by the limiter stage. Limiting action keeps the signal at

inductor, L4. The capacitor divider, C13 and C14,

a predetermined amplitude. The output of the limiter is

provides the feedback between the transistor collector at

applied to a modified Foster-Seeley discriminator stage,

Z1-8 and emitter at Z1-10 to sustain oscillation. The

and the audio information extracted from the fm signal.

injection signal is derived from the oscillator output

f. The audio signal from the discriminator is

circuit and is applied to the first mixer circuit at Z1-6 by

increased by the audio amplifier and applied either to

capacitor C10. Capacitor C12 is the signal bypass for

the horn transducer or headset depending upon which is

the oscillator output circuit. Rf choke, L3, in conjunction

used. The squelch circuit, when applied, is activated by

with capacitors C9 and C12, form a B+ decoupling

the presence of 150 Hz tone signal recovered by the

network providing isolation between the local oscillator

discriminator from the incoming signal and disables the

and the first mixer.

audio amplifier to keep the receiver quiet in the absence

of a signal.

1-7. First Mixer

1-5. Antenna and rf Circuits (fig. 4-10)

The transistor for the first mixer is contained in the

integrated circuit Z1. The rf signal from the rf amplifier

a. The AN/PRR-9(XE-9) receiver antenna E1

is applied through Z1-6 to the input of the first mixer by

(Antenna AS-1998/PRR-9) is a whip-type antenna most

means of the secondary winding of T3 and R1. The

receptive to any direction of horizontal radiation. A

signal from the local oscillator is applied across the

permeability tuned loading coil L1 is used to electrically

combined impedance of R1 and the secondary of TS.

compensate for the physical shortness of the antenna.

The output of the first mixer at Z1-12 is developed

The signal from the antenna is coupled through loading

across the tuned circuit consisting of T4 and C16, which

coil L1 to a double-tuned circuit by means of a low-

is resonant at the first i.f. frequency 10.7 MHz. The

impedance tap of transformer T1. The input tuned

10.7 MHz i.f. signal is coupled from the first mixer at a

circuit consists of variable capacitor C1 and the

reduced impedance level by means of the tap on T4 and

inductance of TI. The rf signal is coupled by capacitor

through capacitor C17 to the input of the 10.7 MHz i.f.

C2 to the other half of the double-tuned circuit,

amplifier at Z2-3. Capacitors C8, C9 and C11 provide

consisting of variable capacitor C3 and the primary

signal bypassing. Rf choke L5, C9 and C22 form a B+

winding of transformer T2. The signal is inductive-

line isolation network between the first mixer and the

coupled to T2 secondary and to Z11 the input of the rf

10.7 MHz i.f. amplifier.

amplifier. The output of the rf amplifier is coupled from

Zi-4 to a tap on the primary of transformer T3. The

1-8. I.f. Amplifier, 10.7 MHz

primary of T3 and variable capacitor C7 form the third

tuned circuit at the rf signal frequency.

The transistor for the 10.7 MHz i.f.

amplifier is

b. The primary to secondary turns ratio of T2 and

contained in the i.f. integrated circuit Z2. The i.f. signal

the tap on the primary of T3 provide the proper

is coupled to the Z2-3 input of the 10.7 MHz i.f.

impedance relationships to maintain stability of the rf

amplifier by C17. The output signal at

amplifier under all voltage and temperature service

conditions and, at the same time, provide adequate

signal gain.

1-2