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(3) A1A AND FSK MODES
The CW8 or FSK8 voltage are applied to the balanced mod-
ulator (IC9, pin 4) to upset the balance and create a carrier
signal.
In A1A mode, the CW keying circuit (IC18a) controls the bias
voltage of the IF amplifiers (Q18, Q19) and T/R switching
diode (D19) to switch the carrier transmission.
In FSK mode, BFO frequency is shifted in the PLL unit to
create the mark and space frequencies.
3-2-3 1ST MIXER CIRCUIT (MAIN UNIT)
The amplified signal from the IF amplifier (Q17) is mixed
with a 60 MHz LO signal at the 1st mixer circuit (D52) to pro-
duce a 69.0115 MHz IF signal. The mixer is commonly used
with the receiver 2nd mixer.
The 69.0115 MHz IF signal passes through the filter (FI1b)
and is then applied to the 2nd mixer circuit.
3-2-4 2ND MIXER CIRCUIT (MAIN UNIT)
The filtered signal is mixed with a PLL output frequency
(1LO: 69.5155–99.0155 MHz) at the 2nd mixer circuit (Q3,
Q4) to produce an RF signal which is the same frequency as
the displayed one.
3-2-5 RF FILTER CIRCUIT (MAIN UNIT)
The RF signal passes through the low-pass filter (L55, L56,
C89–C93, C620, C628) and is then amplified at the RF
amplifier (Q2).
The amplified signal is applied to one of nine RF filters.
These RF filters are commonly used with the receiver circuit
which consists of eight high-pass filters and one low-pass fil-
ter. The filtered signal is amplified at the RF amplifier (Q1)
and is then applied to the PA150W board via J1.
• ALC CIRCUIT
Q18
Q19
IF ALC CIRCUIT
IC17b
IC17a
–
+
High power set (R184)
Low power during tune (Q28)
20 W low power set (Q132)
Current APC
–5 V
MAIN UNIT
D52
Q3, Q4
Q17
Q126
Current APC control (Q111)
Low power during tune (Q21, Q22)
3-2-6 POWER AMPLIFIER CIRCUIT
(PA150W BOARD)
This circuit provides a stable 150 W (at 13.6 V DC) of output
power. The RF signal from the MAIN unit is amplified at the
pre-driver (Q8), driver (Q1, Q2), and power amplifier (Q3,
Q4).
The driver and power amplifiers form class AB push-pull cir-
cuits. Bias voltage to these transistors is produced by diodes
(D1–D3) which have temperature junctions with the transis-
tors.
The amplified signal is then applied to one of eight low-pass
filters to suppress high harmonic components. The filtered
signal passes through the power detector circuit (FILTER
board; L41) and transmit/receive switching relay (FILTER
board; RL17) and is then applied to the antenna connector.
• LOW-PASS FILTERS USED (FILTER BOAED)
Frequency
Control
(MHz)
signal
0.5–1.999
L0
2–2.999
L1
3–4.999
L2
5–6.999
L3
7–9.999
L4
3-2-7 ALC CIRCUIT
The transceiver has two ALC (Auto Level Control) loops for
constant output power over all marine bands and for high
power setting.
(1) IF ALC CIRCUIT (MAIN UNIT)
A portion of the IF signals from the IF amplifier (Q17) is
applied to the IF ALC circuit. The signal is amplified at Q126
and then detected at the ALC detector (D46). The detected
signal is amplified at the ALC amplifier (IC17b) and is then
applied to the comparator (IC17a).
Q2
Q8
Q1
Pre-driver Driver
8 V
IC16b
RF ALC CIRCUIT
3 - 4
Entrance
Frequency
Control
coil
(MHz)
signal
RL1
10–13.999
RL3
14–17.999
18–19.999
RL5
20–21.999
RL7
22–23.999
RL9
24–29.999
PA BOARD
FILTER BOARD
Q1, Q2
Q3, Q4
PA
+
–
–
+
IC16a
Q23
Entrance
coil
L5
RL11
L6
RL13
L7
RL15
L41
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