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TM 11-5820-695-35
crystal diodes CR1 and CR2. A positive dc voltage is
Frequency (MHz)
developed across resistor R1 which is proportional to the
68.20 and 71.81................................ ...... 1.2 to 1.6
de current through crystal diode CR1. This positive dc
67.64 and 72.54................................ ...... 2.6 to 3.4
voltage is sent to the meter selector switch through pin 8
66.58 and 73.59................................ ...... 6.4 to 6.6
of plug P1.
Similarly, a negative dc voltage is
65.15 and 75.19................................ ...... 10.8 to 13.2
developed across resistor R2 which is proportional to the
63.52 and 77.10................................ ...... 17.0 to 23.0
dc current through crystal diode CR2. This negative dc
voltage is also sent to the meter selector switch via pin 9
For Receiver, Radio R-1467(P)A/GRC-144(V), 10,6
of plug P1. Inductors L1 and L2 are used to block the if
MHz bandpass filter assembly 956417 (fig. 2-25.1) is
signal from the diode monitoring circuits, and capacitors
used for 9 Mb/s data rate and equalizer-filter assembly
C1 and C4 provide filtering. A filter in each circuit (C6,
956462 (fig. 2-25.2 is used for 18 Mb/s data rate.
L4, C9, and C8, L6, C13) provides additional filtering of
the if signal.  Resistors R3.  R23, and R4, R22 and
meter decoupling resistors. Resistors R22 and R23 are
2-71  Amplifier-Mixer 2A7 Circuit Functioning (figs.
variable and are used to adjust meter deflection.
2-26 and 2-26.1)
Amplifier-mixer 2A7 converts the 4.4-5.0 GHz rf input
b. First Preamplifier.  The input circuit for first
signal to the 70 MHz if signal. This conversion is made
preamplifier stage Q1 is a parallel resonant circuit.
by mixing the 4.4-5.0 GHz rf input signal with the 4.33 to
Therefore, the resonant frequency and bandwidth of the
5.07 GHz local oscillator signal. The B+ supply (15 vdc)
parallel resonant circuit determines the band of
is provided by decoupling capacitors C5, C10, C14, and
frequencies coupled to the base of first preamplifier
C20. Inductors L5, L8, and L10 block the if signal from
stage Q1. The parallel resonant circuit is formed by L3,
the B+ input. Test point TP2, + 15v, can be connected
C7, the input capacitance of Q1, and the output if
to the meter on meter panel assembly 2A15A2 with a
capacitance of crystal mixer 2A7Z1.  The resonant
test lead and resistor R21 is a meter decoupling resistor.
frequency is set at 70 MHz by adjusting IF ADJ control
L3. Q1 amplifies the 70 MHz if signal passes by the
input circuit, and the amplified 70 MHz if signal is
a. Crystal Mixer 2A7Z1.  The 4.4 to 5.0 GHz rf
coupled by C11 to the base of second preamplifier stage
input signal is applied to input of 2A7Z1 through
02 through capacitor C11. Resistors R5 and R6 provide
connector J1 RF IN and the 4.33 to 5.07 GHz local
fixed dc basis for Q2, and resistor R7 is its collector
oscillator signal is applied to input jack J2 LO IN.
load. Emitter resistor R8 provides negative dc feedback
Crystal mixer 2A7Z1 consists of a matched pair of IN23
to temperature stabilize first preamplifier stage Q1, and
WEMR crystal diodes CR1 and CR2 which mix the rf
capacitor C12 provides the if bypass and tuning.
input signal with the local oscillator signal. Mixing the
two signals produces numerous frequencies, of which,
the four predominant frequencies are: (1) the original
c. Second Preamplifier. Second preamplifier stage
carrier frequency, (2) the original local oscillator
Q2 also amplifies the 70 MHz if signal, and the output is
frequency, (3) the sum of the two frequencies, and (4)
coupled by C15 to the base of third preamplifier Q3.
the difference between the two frequencies (70 MHz).
Resistors R9 and R10 provide fixed dc bias for this
Only the 70 MHz difference frequency is applied to the
stage and inductor L7 is its collector load. Resistor R11
input circuit of first preamplifier Q1, through coupling
provides negative ac feedback to stabilize second
capacitors C2, C3, and C7.  All other frequencies
preamplifier
produced by the mixing process are rf bypassed to
ground in crystal mixer 2A7Z1. Additional outputs are
provided which permit monitoring the dc current through
Change 6
2-113


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