Other Circuits; Port Allocations - Icom IC-F43GT Service Manual

4-5 OTHER CIRCUITS

4-5-1 COMPANDER CIRCUIT (MAIN UNIT)
IC-F43GT/GS/F44GT/GS have compander circuit which can
improve S/N ratio and become wide dynamic range. The cir-
cuit is composed in the base band IC (IC14).
(1) IN CASE OF TRANSMITTING
The audio signals from the microphone are applied to the
base band IC (IC14, pin 3) via microphone amplifier (IC23).
The signals are amplified at the amplifier section, and are
then applied to the compressor circuit to compress the audio
signals. The signals pass through (or bypass) scrambler
section, and are then applied to the limiter section after
being passed through the high-pass filter. The filtered sig-
nals pass through the splatter filter section, and are then
applied to the modulation circuit (D12) via the FM/PM switch
(IC13), low-pass filter (IC6) and D/A converter (IC12).
(2) IN CASE OF RECEIVING
The demodulated AF signals from the IF IC are applied to
the amplifier section in base band IC (IC14, pin 23), and
then pass through the low-pass and high-pass filter section
to suppress unwanted signals. The filtered signals pass
through (or bypass) scrambler section, and are then applied
to the expander circuit to expand AF signals. The signals are
applied to the base band IC's amplifier section (IC14, pins
19, 20), and are then applied to the AF amplifier circuit.
• BASE BAND IC BLOCK DIAGRAM
TXINO
4
VR1 Com-
TXIN 3
(HPF) pressor
TXA1
RXINO 22
VR3 RX
RXIN 23
(HPF) LPF
RXA1
SDEC 21
MTDT 10
MTCK 9
MDIR 14
MSCK 13
Control
MDIO 11
Register
MRDF 12
Pre-
emphasis
TX/RX
HPF
MSK
Modulator
MSK MSK
BPF Demodulator

4-6 PORT ALLOCATIONS

4-6-1 D/A CONVERTOR IC (IC12)
Pin Port
number name
10 BAL
14 TLVA
15 RLVA
22 T1
23 T2
Limiter
Scrambler/
De-scrambler
De-
emphasis
4 - 5
Description
Outputs the modulation balance level
control signal. The signal is applied to
the buffer amplifier (IC24, pin 1).
Outputs the TX VCO lock voltage con-
trol signal.
Outputs the RX VCO lock voltage con-
trol signal.
Outputs the bandpass filter tuning sig-
nal. The output signal is applied to the
bandpass filters (D19, D20, D24,
D25).
• Outputs the bandpass filter tuning
signal. The output signal is applied to
the bandpass filters (D14, D15).
• Outputs the TX power control signal.
The output signal is applied to the
APC amplifier (IC16, pin 1).
Splatter VR2 SMF
18
Expander VR4
19
20 SIGNAL
RXA2
7 MOD