Icom IC-F50V Service Manual page 10

The applied MIC signals are amplified at the amplifier
(TXA1), and level adjusted at the volume controller (VR1).
The level adjusted MIC signals are applied (bypassed) the
compressor section, pre-emphasis section, TX/RX HPF,
de-scrambler, limiter, splatter, in sequence, then applied to
another volume controller.
The compressor compresses the MIC signals to provide
high S/N ratio for receive side, and the pre-emphasis obtains
+6 dB/oct audio characteristics. The TX/RX HPF fi lters out
250 Hz and lower audio signals, the limiter limits its level and
the splatter fi lters out 3 kHz and higher audio signals. The
filtered MIC signals are level adjusted at another volume
controller (VR2), and then output from pin 7 via smoothing
fi lter (SMF).
The output MIC signals are passed through the FM/PM
SW (IC11, pins 6, 1) and LPF (IC5, pins 2, 1) then applied
to the DAC (D/A Converter; IC6, pin 4) and level-adjusted
(deviation adjustment). The level-adjusted MIC siganls are
output from pin 3, then applied to the modulation circuit as
the modulation signals "MOD" via buffer (IC5, pins 6, 7).
MODULATION CIRCUIT
The modulation circuit FM-modulates the VCO oscillating
signal with the modulation signals from the TX AF circuits.
• VOICE SIGNAL
The buffer-amplified AF signals are applied to the variable
capacitor (VD) to change its reactance for FM modulation.
• TONE SIGNALS
Tone signals are generated in the CPU and applied to the
both of the VCO and reference frequency oscillator to be
modulated.
• MODULATION CIRCUIT AND TX/RX VCOs
R9 8
L28
Freq.
adjust
LV
TX VCO
L27
Freq.
adjust
MOD
RIPPLE
Q17
FILTER
RX VCO
R8 5
L2 6
C127 C126
R81
L3 9
R8 4
Modulation
C124 L25
C123
L43
L3 8
<CTCSS/DTCS>
CTCSS/DTCS signals ("CEN0"–"CEN2") are generated by
the CPU (F: IC401, pins 79–81) and converted its wave
form by R461–R463 (F), then passed through the LPF (F:
IC403, pins 3, 1). The fi ltered CTCSS/DTCS signals are
then level-adjusted by DAC (M: IC6, pins 9, 10) and applied
to the AF mixer (M: IC5, pin 2) to be mixed with MIC signals,
then applied to the TX VCO as the modulation signals. The
CTCSS/DTCS signals are also applied to the reference
signal oscillator (M; X2) too, via the buffer (M: IC16, pins 2, 1).
<2/5 TONE, DTMF>
2/5 tone and DTMF signals are ("SEN0"–"SEN3") are
generated by the CPU (F: IC401, pins 72–75) and converted
its wave form by R471–R474 (F), then passed through
the two-staged LPF (F: IC403, pins 5, 7 and pins 10, 8).
The filtered 2/5 tone and DTMF signals are applied to the
AF mixer (M: IC5, pin 2) to be mixed with MIC signals.
The mixed signals are then applied to the TX VCO as the
modulation signals). The CTCSS/DTCS signals are also
applied to the reference signal oscillator (M: X2, pin 1) too,
via the buffer (M: IC16, pins 2, 1).
The modulated VCO output is buffer-amplifi ed by two buffers
(Q12, Q10), and applied to the pre-driver via TX/RX SW.
R7 9
Q14
C 102
Q12
BUFFER
R8 3
Q13
Q15
5 1
R82
2
R88
4 3
VCO
SW
from VCO
4 - 4
VCC
T5V
TX/RX
SW
D14
C100
TX
R72
D15
Q11
Q10
BUFFER BUFFER
LPF
L14
Q16
C49
C93