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
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.
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