CPLR TUNE KW Functional Operation (cont)

TM 11-5820-873-34

amplifier.

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

watts).

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

1A3A1CR7.

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

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

1A3A1Q3.

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

audio

enable/disable

switch

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

mixer.

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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