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Page Title: Frequency Synthesizer System Second Mixer Module A12
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ing network consisting of capacitors C6
and A10J1 and current-limiting re-
and C7 and transformer T3 to fss second
sistor R7 to the anode of CM. This
mixer module A12 (para 26). This circuit
positive voltage forward biases
minimizes spurious frequency injection
CR2; the diode conducts heavily and
into the second mixer.
allows the regenerative circuit to
b. The 53-mc signal from first mixer
crystals Y13 and Y14 to be com-
modu1e A14 is coupled to the filter
pleted. If the RT-505/PRC-25 is
through transformer T1 to a triple-tuned
operating on a 100-kc channel (31.0
network. The three tuned circuits are the
mc, 74.20 mc, etc), S1A will be in
secondary of T1 and C1, L1 and C3, T2
the position shown and crystal Y13
and C5. Capacitors C2 and C4 are coupl-
(5.60 mc) will be selected through
ling capacitors. This triple-tuned network
contacts 8 and 11 of S1A to com-
p r o v i d e s a 2-mc bandpass at the 3-
plete the regenerative circuit to
decibel (db) points. The output of this net-
the emitter of Q2. If the RT-505/
work is coupled to second mixer module
PRC-25 is operating on a 50-kc
channel (31.15 mc, 74.25 mc, etc),
S1A will be turned clockwise one
position from that shown and crys-
26. Frequency Synthesizer System Second
tal Y14 (5.55 mc) will be selected
Mixer Module A12
through contacts 8 and 9 of S1A to
complete the regenerative circuit
to the emitter of Q2.
The fss second mixer module heter-
odynes the output from 53-mc filter A13
(4) Capacitor C7 is an rf bypass ca-
pacitor. Capacitor C8 is a coupling
(para 25), with the 46.85-mc to 47.75-mc
capacitor between the base and
output of the 100-kc interval oscillator
collector circuit. Resistors R10,
(applied through A13) to produce an fss
R11, and R12 develop fixed bias;
if. of 5.55, 5.60, or 5.65 mc. This output
resistors R8 and R9 are emitter
is applied to fss if. amplifier module A18
swamping resistors for Q2.
c. Buffer Q3.
a. The 53-mc input from module A13
(1) The output from oscillator Q2 is
is coupled through capacitor C1 to the
base of Q1. The 46.85-mc to 47.75-mc in-
coupled through transformer T2
put from A13 is coupled through capacitor
to the base and emitter of Q3. The
buffer isolates Q2 from any varying
C2 to the emitter of Q1. Transistor Q1
heterodynes these two input signals; the
loading effects.
resultant output signals at the collector of
(2) Resistors R14, R15, and R16 de-
Q1 are applied to the frequency selective
velop fixed-base bias. Resistor
R13 is the emitter swamping resis-
tor. Capacitors C11, C12, and C13
b. The frequency selective network is
are rf bypass capacitors. Inductor
composed of capacitors C4 through C7,
L2 and capacitor C15 form a de-
variable transformers T1 and T2, and
coupling network to prevent
variable inductors L1 and L2. The outputs
rf leakage into the power supply.
from Q1 are the two original frequencies
plus their sum and difference. The fre-
The rf output from Q3 can be mess -
ured at test jack J3.
quency selective network passes only the
difference frequency. The network is a
bandpass filter having a flat characteristic
25. 53-Mc FiIter A13
resonant frequency of 5.6 mc.
c. Resistor R5 and capacitor C 3 filter
rf signals from the +10-volt dc supply.
The 53-mc filter has two input signals.
Resistors R1 and R2 provide the fixed-base
a. The output signal from 100-kc in-
terval oscillator module A 10 is coupled
bias. Resistor R3 is the emitter swamping
resistor. Resistors R4 and R6 terminate
through isolation resistor R1 and a match-

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