5 - 3
Splat.
IC16
AMP
IC16
AMP
IC5
MIC
line
SW
MIC
D/A
IC14
CD4066
IC18
MICROPHONE
CONNECTOR
J1
FRONT UNIT
MIC
BAL
To the Reference
frequency oscillator
MODI
MCOT
MCGO
TONE
CDTS
MOD
VRAF
TX VCO
SPIN
REF
OSC
X2
CR-794
TX/RX
SW
D14,D15
Q13,D16,31
FIL
LOOP
PLL
IC
IC4
MB15A02
FM
MOD
D18
BUFF
Q10
BUFF
Q11
IC19
AMP
REF
TX VCO
BAL
15.3 MHz
From the D/A converter
From the MIC line SW
To TX AMPs
LV
LPF
LPF
LPF
LPF
PWR
DET
D1,D11,D12
MUTE
SW
D28
ANT
SW
D3
PWR
AMP
IC
RX circuits
3
APC
AMP
IC2
DRIVE
AMP
Q9
T1
TMUT
136-174 MHz
From TX VCO
5-2 TRANSMITTER CIRCUITS
MIC AMPLIFIER (FRONT UNIT)
Audio signal from the connected microphone is applied to
the MIC AMP (IC5), through the microphone connector (J1).
The amplifi ed MIC signal is applied to the MAIN UNIT.
TX AF CIRCUITS (MAIN-A UNIT)
The MIC signal from the FRONT UNIT is passed through
the D/A converter (as a MIC gain controller; IC18) for level
adjustment, and applied to the limiter AMP which is also
rolled to the pre-emphasis circuit (IC16).
• TX AF CIRCUITS
MIC MUTE SWITCH (MAIN-A UNIT)
The pre-emphasized MIC signal is passed through the MIC
mute SW (IC14).
While receiving, the MIC mute SW (IC14) cuts the MIC line
off, and is controlled by “MMUT” signal from the expander
(IC17).
SPLATTER FILTER (MAIN-A UNIT)
The MIC signal from the MIC mute SW (IC14) is applied to
the splatter fi lter (IC16).
The splatter filter (IC16) is also used as the AF Summing
AMP for tone signal modulation (CTCSS, 2/5 TONE).
MODULATION CIRCUIT (MAIN-A UNIT)
MIC signal from the splatter filter (IC16) is level-adjusted
(=deviation adjustment) by the D/A conver ter (IC18),
and applied to the TX VCO (Q13, D16, 31), through the
modulation mute SW (IC14) as the modulation signal.
The MIC signal is also applied to the reference frequency
oscillator (X2) as the modulation signal, through D/A
converter (IC18) and REF AMP (IC19).
• MODULATION CIRCUITS
CTCSS/DTCS SIGNALS ENCODING (FRONT UNIT)
The CTCSS/DTCS encoding signal from the CPU (IC1)
“CENC0–CENC2” is passed through the LPF (IC5) for
waveform conversion, and applied to the MAIN UNIT as tone
modulation signal.
2/5 TONE, DTMF ENCODING (FRONT UNIT)
Encoding signal from the CPU (IC1) named “SENC” is
passed through the LPF (IC5), and applied to the MAIN
UNIT as tone modulation signal.
TX AMPLIFIERS (MAIN-A UNIT)
The frequency-modulated signal from the TX VCO is buffer-
amplifi ed by two buffers (Q11 and Q10), and applied to the
drive AMP (Q9) as the TX signal through the LO SW (D14).
The amplifi ed TX signal is applied to the FET HPA module
(IC3) through the LPF, and power-amplified to obtain TX
output power level.
The power-amplified TX signal is passed through the
antenna SW (D3) and LPF as a harmonic filter, and then fed
to the antenna.
APC CIRCUIT (MAIN-A UNIT)
A portion of TX signal rectifi ed by D1, D11 and D12 on the
TX line to detect TX power level. The rectified voltage is
applied to the APC AMP (IC2), and the APC AMP controls
the gain of HPA module (IC3) automatically by comparing
the rectifi ed voltage and the power setting voltage "T1."
• TX AMPLIFIERS APC CIRCUIT
