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Page Title: CPLR TUNE KW Functional Operation (cont)
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TM 11-5820-873-34
The output from amplifier 1A3A2Q1,
(1)  Power supply 1A6 (para 2-7) provides the
1A3A2Q2 is coupled to 2nd balanced mixer 1A3A1CR9
regulated DC voltages required to operate the circuits in
thru 1A3A1CR12 ALC amplifier 1A3A3Q9, 1A3A3Q10
the RT-1277/URC-92.
has no effect on 1A3A2Q1, 1A3A2Q2. If no VSWR ALC
(2)  TCXO  1A8U1  is  an  extremely  stable,
signal, PA high voltage or PA high current ALC input
temperature controlled, crystal oscillator and provides
voltages are present at the inputs of 1A3A3Q9 &
the 5 MHz reference signal to the synthesizer.
1A3A3Q10. The voltage ALC does not take effect until
(3)  Synthesizer 1A4 (para 2-8) generates three
the  transmitter  output  reaches  100  watt  peak
local oscillator frequencies.  The 1st local oscillator
(transmitter output in CPLR TUNE KW mode is 30 to 40
frequency of 91.25 to 121.2499 MHz is controlled by the
selected  front  panel  FREQUENCY  switches  and
(8)  The nominal 80.75 MHz, 2nd local oscillator
determines the operating frequency of the radio. The
signal from synthesizer 1A4 is coupled to the 2nd
2nd local oscillator frequency is 80.75 MHz. And, the
balanced mixer through 2nd local oscillator amplifier
3rd local oscillator frequency is 10.5 MHz.
1A3A1Q8. The output from the 2nd balanced mixer is
(a)  The 3rd local oscillator signal is derived by
couple to amplifier 1A3A1Q7.
direct synthesis techniques (i.e. by dividing and mixing
(9)  Amplifier 1A3A1Q7 is enabled by the transmit
the output of 1A8U1). This local oscillator signal is used
enable signal and amplifies the output from the 2nd
to generate the carrier signal.
balanced mixer.  The 91.25 MHz (sum frequency)
(b)  The 2nd local oscillator consists of a crystal
output signal from 1A3A1Q7 is coupled through VHF
oscillator at a nominal frequency of 80.75 MHz. This
filter 1A3A1FL1 to 1st balanced mixer 1A3A1CR4 thru
frequency is used in VHF mixer 1A3A1 to convert the
1st IF of 91.25 MHz to the 2nd IF of 10.5 MHz. Since
(10) The 91.25 MHz to 121.2499 MHz, 1st local
the 2nd local oscillator is not referenced to 1A8U1, a
oscillator signal from synthesizer 1A4 is coupled to the
small frequency error can exist. However, because of
1st balanced mixer through 1st local oscillator amplifier
the mixing scheme used, this same error appears on the
1A3A1Q5.  The nominal frequency of the 1st local
1st local oscillator signal and is therefore canceled at
oscillator signal is 91.25 MHz plus the setting of the
the output of the VHF mixer.
selected FREQUENCY switches.
(If the selected
(c)  The VCO (1st local oscillator) is a phase
FREQUENCY switches are set to 12.3456, the 1st local
locked oscillator covering the frequency range of 91.25
oscillator frequency is 103.5956 MHz.) The output of
to 121.2499 Hz in 100 Hz steps. The exact frequency of
the 1st balanced mixer is coupled to amplifier 1A3A1Q1,
the 1st local oscillator is equal to 91.25 MHz plus the
setting of the selected FREQUENCY switches and the
(11) The gain of amplifier 1A3A1Q1, 1A3A1Q3 is
difference between the frequency of the 2nd local
controlled by the output of current ALC amplifier
oscillator and 80.75 MHz.  The 1st local oscillator is
1A3A1Q4 ((13) below). The current ALC amplifier limits
used to convert the 1st IF frequency of to 91.25 MHz to
the gain of 1A3A1Q1, 1A3A1Q3 during high current
the selected operating frequency.
peaks. Amplifier 1A3A1Q1, 1A3A1Q3 is enabled by the
(4)  Transmit
transmit enable signal and amplifies the difference
1A3A5Q1 is turned off by the audio disable from mode
frequency (equal to the setting of the selected
switch 1A1S13. This blocks the transmit enable from
FREQUENCY switches) output of the 1st balanced
1A8K1 and 3rd local oscillator amplifier 1A3A3Q1 is not
enabled. With no 10.5 MHz input, balanced modulator
(12) RF power amplifier 1A7A1Q1 thru 1A7A1Q6
1A3A3CR3 thru 1A3A3CR6 has no output and audio can
is enabled by the transmit enable signal and amplifies
not enter the IF circuits.
the HF signal from 1A3A1Q1, 1A3A1Q3 to the 100 watt
(5)  The AM/CPLR TUNE KW transmit enable
level (30-40 watts AM & CPLR TUNE KW). The output
signal is coupled from mode switch 1A1S13 through
from the RF power amplifier is coupled through the
relay 1A8K1 to turn on AM transmit switch 1A3A3Q13.
selected low pass filter (para 2-10) to ANT jack 1A8J1.
The AM transmit switch enables automatic carrier
(13) Current ALC detector 1A7A1Q7 monitors the
control amplifier 1A3A3Q2, 1A3A3Q3, and 1A3A3Q5.
supply current to the RF power amplifier.  When the
The gain of the automatic carrier control amplifier is
supply current exceeds 10 amperes, 1A7A1Q7 is turned
established by the setting of 1A3A3R18.
on causing current ALC amplifier 1A3A1Q4 to reduce
(6)  The 10.5 MHz, 3rd local oscillator signal from
the gain of amplifier 1A3A1Q11, 1A3A1Q3.
synthesizer 1A4 is amplified by the automatic carrier
(14) Power output detector 1A5A4CR5 samples
control amplifier and coupled to the input of amplifier
the voltage on the RF output line.  The output from
1A3A2Q1, 1A3A2Q2.
1A5A4CR5 drives meter 1A2M1 when FWD power is
(7)  Amplifier 1A3A2Q1, 1A3A2Q2 is enabled by
selected by 1A2S1.
the transmit enable signal and amplifies the 10.5 MHz
carrier signal from the automatic carrier control

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