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4-2 TRANSMITTER CIRCUITS
4-2-1 MICROPHONE AMPLIFIER CIRCUIT
(MAIN AND CONTROL UNITS)
The microphone amplifier circuit amplifies audio signals from
the microphone to a level needed for the modulation circuit.
The microphone amplifier circuit is commonly used for the
both VHF and UHF bands.
• THE AF SIGNALS FROM THE MAIN UNIT
The AF signals from the microphone (J2001, pin 6) pass
through the high-pass filter (Q2028), and are then applied to
the microphone amplifier (IC2014, pin 3). The amplified sig-
nals are applied to the analog switch (IC2008, pin 1).
The microphone sensitivity is controlled by the microphone
sensitivity controller (Q2023) via the "MIC_SENS" line from
the CPU (IC2023).
•THE AF SIGNALS FROM THE CONTROL UNIT
The AF signals from the microphone (CONTROL unit; J1, pin
6) are applied to the microphone amplifier (Q15, IC5 pin 3).
The amplified signals pass through the J2, pin 2 via the "MIC"
line, and are then applied to the analog switch (IC2008, pin
4).
The microphone sensitivity is controlled by the microphone
sensitivity controller (Q2022) via the "MIC_SENS" line from
the CPU (IC2023).
The each AF signals (from IC2008, pins 1, 4) are applied to
the IDC limiter amplifier section (IC1000a, pin 3), and then
pass through the de-emphasis circuit (C1036, R1050). The
signals pass through the splatter filter (IC1000d, pins13, 14),
and are then applied to the buffer amplifier (IC1000c, pin 9).
The amplified signals are applied to the D/A convertor IC
(IC1009, pin 12) to control the modulation level.
• THE DATA SIGNALS
(1) 9600 bps mode
The data signals from the J2003, pin 1 are applied to the
analog switch (IC2007, pin 4) after being passed through the
limiter circuit (D2012). The signals pass through another ana-
log swtich (IC2008, pins 9 and 8), and are then applied to the
buffer amplifier (IC100c, pin 9) via the "DATAMOD" line. The
amplified signals are applied to the D/A convertor IC (IC1009,
pin 12) to control the modulation level.
(2) 1200 bps mode
The data signals from the J2003, pin 1 are applied to the
analog switch (IC2007, pin 4) after being passed through the
limiter circuit (D2012). The signals pass through another ana-
log swtich (IC2008, pins 10 and 11), and are then applied to
the IDC limiter amplifier section (IC1000a, pin 3). The signals
pass through the de-emphasis circuit (C1036, R1050) and
splatter filter (IC1000d, pins13, 14). The signals are amplified
at the buffer amplifier (IC1000c, pin 9), and are then applied
to the D/A convertor IC (IC1009, pin 12) to control the modu-
lation level.
The AF or data signals are applied to the each VCO circuit
from the D/A convertor IC (IC1009, pin 11) as "MOD" signal.
4-2-2 VHF MODULATION CIRCUIT
(MAIN AND VCO UNITS)
The modulation circuit modulates the oscillating signal (RF
signal) using the microphone audio signals.
The "MOD" signal from the D/A convertor IC (IC1009, pin 11)
changes the reactance of D5 (VCO unit) to modulate the
oscillated signal at the VHF-VCO circuit (VCO unit; Q6). The
modulated signal is amplified at the buffer amplifiers (VCO
unit; Q7, Q8), and then passes through the VCO swtich
(VCO unit; D12, D13). The TX LO signal passes through the
low-pass filter (L90, L91, C245–C247) and attenuator
(C2134, R2216–C2218), and is then applied to the TX switch
(D77) via the "VHF_YGR" line. The signal is applied to the
drive/power amplifier circuits.
4-2-3 UHF MODULATION CIRCUIT (MAIN UNIT)
The "MOD" signal from the D/A convertor IC (IC1009, pin 11)
changes the reactance of D1018 to modulate the oscillated
signal at the UHF-VCO circuit (Q1039). The modulated sig-
nal is amplified at the buffer amplifiers (Q1044, Q1047), and
then passes through the VCO swtich (D2059, D2060). The
TX LO signal passes through the high-pass filter (L1079,
C2183, C2184), and is then applied to the TX switch (D78)
via the "UHF_YGR" line. The signal is applied to the
drive/power amplifier circuits.
4-2-4 DRIVE/POWER AMPLIFIER CIRCUITS
(MAIN UNIT)
The drive amplifier circuit amplifies the VCO oscillated signal
to the needed level at the power amplifier. Q27 is a power
module which provides stable 50 W (UHF is 35 W) output
power with a 13.8 V DC power source.
The RF signal from the TX switch (D77; VHF, D78; UHF) is
amplified at the buffer amplifier (Q38), and is then applied to
the pre-amplifier (Q16). The amplified signal is amplified at
the pre-drive (Q21) and drive amplifier (Q25), and then
applied to the power amplifier (Q27) to obtain 50 W (UHF is
35 W) of RF power.
• VHF RF SIGNAL
The amplified signal passes throught the low-pass filter (D36,
D2070), and is then applied to the SWR detector (D57, D61).
The signal is applied to the TX/RX switch (D42), and passes
through the low-pass filter (L76, L77, L80, C205, C209,
C242, C243, C264) to suppress high harmonics compo-
nents. The signal is applied to the antenna connector after
being passed through the reverse power detector circuit
(D70, D71).
• UHF RF SIGNAL
The amplified signal passes throught the TX/RX swtich (D37,
D38, D41, D43–D45, D68), and is then applied to the SWR
detector (D50, D58). The signal passes through the high-
pass filter (L78, L81, C206, C210, C213, C265) to suppress
high harmonics components. The signal is applied to the
antenna connector after being passed through the reverse
power detector circuit (D70, D71).
The detected voltage at the reverse detector ciruit is applied
to the CPU (IC2013, pin 35) to switch from high power to
middle power automatically when the SWR become worse.
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