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Page Title: Synthesizer 1A4 Detailed Functional Operation
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TM 11-5820-873-34
(5)  17 MHz Reference Generator.  The third
harmonic of the 1 MHz pulse from 1A4A1U4 ((2) above)
Operation (Fig. FO-3, and FO-18 thru FO-23)
is amplified by 3 MHz amplifier 1A4A1Q5. The 3 MHz
The synthesizer generates the three local oscillator
output from 1A4A1Q5 is applied to 17 MHz mixer
injection frequencies used in the IF circuits of the radio.
1A4A1Q6. The other input to 1A4A1Q6 is the 20 MHz
The 3rd local oscillator frequency is fixed at 10.5 MHz
signal from 1A4A1U3 ((1) above). The two inputs are
and is generated by spectrum generator 1A4A1 (a
mixed in 1A4A1Q6 and the 17 MHz difference
below). The 2nd local oscillator frequency is fixed at
frequency is filtered by the bandpass filter. The 17 MHz
80.75 MHz and is generated by translator 1A4A3 (c
output of the bandpass filter is coupled through amplifier
below).  The 1st local oscillator frequency is variable
(complementary emitter follower) 1A4A1Q7, 1A4A1Q8
and controls the operating frequency of the radio. The
to low digit generator 1A4A2 (b below).
1st local oscillator frequency is generated by VCO
(6)  21 MHz Reference Generator.  The 1 MHz
1A4A5 (e below). The signals used to control the 1st
pulse from 1A4A1U4 ((2) above) is filtered by the 1 MHz
local oscillator frequency are generated in other areas of
bandpass filter. The 1 MHz sinewave from the 1 MHz
the synthesizer. The frequency of some of these signals
bandpass filter is amplified by complementary emitter
is controlled by the setting of the selected FREQUENCY
follower 1A4A1Q1, 1A4A1Q2.  The 1 MHz sinewave
control switches.  Table 2-1 lists the points where
from the complementary emitter follower is applied to
programmed frequencies and division ratios can be
balanced mixer 1A4A1CR4 thru 1A4AiCR7. The other
found in the synthesizer.  The table also shows the
input to be balanced mixer is the 20 MHz signal from
frequency or division ratio at these points for various
1A4A1U3 ((1) above).
The 20 MHz signal from
settings of the selected FREQUENCY control switches.
1A4A1U3 is amplified by 1A4A1U8 and applied to the
a. Spectrum Generator 1A4A1 (Fig. FO-3 and Fig.
balanced mixer. The 21 MHz sum frequency is filtered
by the 21 MHz bandpass filter and amplified by
(1)  20 MHz Reference Generator.  The 5 MHz
The 21 MHz signal from 1A4A1U9 is
reference signal from TCXO 1A8U1 is amplified by
coupled through emitter follower 1A4A1Q9 to translator
1A4A1U1 and clipped by the diode clipper. The positive
1A4A3 (c below).
going half waves from the diode clipper are inverted by
(7)  10.5 MHz 3rd Local Oscillator Signal. The 21
1A4A1U2A.  The output of 1A4A1U2A is applied to
MHz signal from 1A4A1U9 ((6) above) is coupled to
divide-by-5 counter 1A4A1U4 ((2) below) and one shot
divide-by-2  counter  1A4A1U10.
When  the  RT-
1A4A1U2B, 1A4A1U2C. The 5 MHz pulse from the one
1277/URC-92 is operating in the AM receive mode, or if
shot is inverted by 1A4A1U2D. The fourth harmonic of
the setting of the selected 1 MHz FREQUENCY switch
this 5 MHz pulse (20 MHz) is filtered by the 20 MHz
is changed while transmitting switch 1A4A1Q3 is turned
bandpass filter and amplified by 1A4A1U33.  The 20
on disabling 1A4A1U10. At all other times 1A4A1Q3 is
MHz pulse output from 1A4A1U3 is applied to low digit
off and 1A4A1U10 divides the 21 MHz input by 2. The
generator 1A4A2 (b below), 17 MHz mixer 1A4A1Q6
10.5 MHz output from 1A4A1U10 is coupled through
((5) below) and 20 MHz amplifier 1A4A1U8 ((6) below).
emitter follower 1A4A1Q4 to receiver/exciter 1A3.(para
(2)  1 MHz Reference Generator.  The 5 MHz
signal from inverter 1A4A1U2A ((1) above) is applied to
b. Low Digit Generator 1A4A2 (Fig. FO-3 and Fig.
divide-by-5 counter 1A4A1U4. The 1 MHz output from
1A4A1U4 is applied to divided-by-10 counter 1A4A1U5
(1)  Voltage Controlled Oscillator 1A4A2.  VCO
((3 below), through the 1 MHz bandpass filter to
1A4A2Q1, 1A4A2Q2 is a Colpitts oscillator with a
amplifier 1A4A1Q1, 1A4A1Q2 ((6) below) and to 3 MHz
frequency range of 15 0 to 15 999 MHz. The oscillating
amplifier 1A4A1Q5 ((5) below).
frequency of the VCO is equal to the setting of the
(3)  100 kHz Reference Generator.  The 1 MHz
selected 10 kHz, 1 kHz and 100 Hz FREQUENCY
pulse from 1A4A1U4 ((2) above) is applied to divideby-
switches times 10, plus 15 MHz.  Coarse frequency
10 counter 1A4A1U5 The 100 kHz output from
tuning is provided by the action of the coarse frequency
1A4A1U5 is applied to VHF divider 1A4A4 (d below) and
voltage (from the selected 10 kHz FREQUENCY switch)
to divide-by-10 counter 1A4A1U6 ((4) below)
on varactor diodes 1A4A2CR1, 1A4A2CR2.
(4)  1 kHz Reference Generator.  The 100 kHz
frequency control is provided by comparing the output of
pulse from 1A4A1U5 ((3) above) is applied to divideby-
the VCO with the 17 MHz and 1 kHz signals from
10 counter 1A4A1U6 The 10 kHz pulse from 1A4A1U6
spectrum generator 1A4A1 (a above). Phase detector
is applied to divlde-by-10 counter 1A4A1U7 The 1 kHz
1A4A2U2 ((4) below) develops an output voltage that is
pulse from 1A4A1U7 is applied to low digit generator 1
proportional to the difference between the frequency of
A4A2 (b below).
the VCO and the desired frequency of the VCO This
voltage is applied to varactor

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