4 - 2
• RX AF CIRCUITS
• TX AF CIRCUITS
• TX AMPLIFIER AND APC CIRCUITS
• MODULATION CIRCUITS
AF
AMP
J3
SP1
LPF
HPF
-> 2nd IF circuits
AF OUT
SP
Q20
IC7
LOGIC UNIT
MAIN UNIT
ANALOG
SW
IC6
TXAF/
RXAF
TXAF/
RXAF
IC3b
RXAF
IC3c
IC28
ANALOG
SW
ELEC.
VOL
IC25
RXAF
MICAF/
RXAF
VOLOUT
(VOUT2)
SP
SW
Q36-Q38
SP
MUTE
ANTENNA
LPF
ANT
SW
TX/RX
SW
PWR
AMP
DRIVE
PRE
APC
CTRL
DRIVE
AMP
BUFF
PWR
DET
D24-D25
D29-D32
D27,D33
RX circuits
IC9b,Q31
Q29
D12-D13
-> TX VCO
MAIN UNIT
Q22
Q26
T2_APC(D/A)
TXMUTE(EXP)
Q21
LPF
MIC
AMP
IC3d
MIC
JACK
LOGIC UNIT
EXT MIC
MODIN
TXAF
AF SW
IC6
TXAF/RXAF
TXAF/RXAF
IC3b
IC28
AF SW
ELECTRONIC
VOLUME
IC25
MICAF/
RXAF
TXAF
(VOUT1)
MICAF
MICAF
IDC
BUFF
LO
AMP
FIL
LOOP
PLL
IC
D/A
IC10
Q17
Q13,D7-D9
REF
OSC
X1
IC1
MAIN UNIT
MOD
MODIN
IC5
(15.3MHz)
W/N
CTRL.
Q11
MOD
REFMOD
RX AF CIRCUITS
The demodulated AF signal from the MAIN UNIT is passed
through the HPF (IC3c), AF line SW (IC6), LPF (IC3d), AF
line SW (IC6), another AF line SW (IC28) and the electronic
volume (IC25) for adjustment in level. The level-adjusted AF
signal is applied to the MAIN UNIT.
The AF signal is applied to the AF AMP (IC7), through the
speaker mute SW (Q20). The amplifi ed AF signal is output
to the internal speaker through the speaker mute SWs (Q33,
Q35–Q37), or external speaker through the speaker mute
SW (Q36, Q37) and the [SP] connector.
SQUELCH CIRCUIT
The squelch circuit cuts off the AF output signal while no RF
signal is received. Detecting noise components in the demod-
ulated AF signal, the squelch circuit stops audio signal from
being emitted.
A portion of the demodulated AF signal from the IF IC (IC3) is
passed through the D/A converter (IC5) for level (=threshold)
adjustment. The level-adjusted AF signal is passed through
the noise fi lter (IC3, pins 7, 8 and R37, R39, R40, R191, C52,
C53, C308) to fi lter only the noise components (approximate-
ly 30 kHz signals). The noise components are rectifi ed by the
noise detector, resulting in a DC voltage corresponding to the
noise level.
When the noise level is higher than the preset one, the inter-
nal comparator sets the “NOIS” signal to the CPU to “High,”
and then the CPU controls the speaker mute SW (Q20) to
stop audio signal from being emitted.
4-2 TX AF CIRCUITS
The AF signal from the microphone (MIC signal) is applied to
the MIC AMP (IC3a), through the
[MIC]
jack. The amplifi ed
MIC signal is passed through the AF line SW (IC28) and the
electronic volume (IC25) for adjustment in level. The level-
adjusted AF signal is applied to the IDC (IC3d) which func-
tions as the splatter fi lter.
The fi ltered MIC signal is passed through another AF line SW
(IC6) and LPF (IC3b), then fed back to the AF line SW (IC6),
and then applied to the modulation circuit on the MAIN UNIT.
MODULATION CIRCUIT
The MIC signal from the LOGIC UNIT is applied to the D/A
convertor (IC5) for adjustment in level (=deviation). The level-
adjusted MIC signal is applied to the TX VCO (Q13, D7–D9)
as a modulation signal.
The modulated TX VCO output signal is amplifi ed by the LO
AMP (Q17), and then applied to the TX AMP circuit as the TX
signal, through the buffer (IC10), LO SW (D13) and another
buffer (Q21).
TX AMP CIRCUITS
The TX signal is sequentially amplifi ed by the pre-drive (Q22),
drive (Q26) and power AMP (Q29). The amplifi ed TX signal is
applied to the antenna, through the ANT SW (D24, D25) and
LPF (L36, L39, L41, L42, C291, C295, C296, C298, C300,
C303, C304, C306, C307).
APC CIRCUIT
The voltage produced on both sides of L39 is rectifi ed by D27
and D33, and used as the TX power sensing voltage. The
voltage is applied to the APC AMP (IC9b), and the output
voltage controls the gate voltages of Q29, Q26 and Q22.
The voltage difference between both sides of R157 is detect-
ed by IC9d, to control the TX power when abnormal current
is detected.
