Other Circuits; Port Allocations - Icom IC-F33GT Service Manual

4-5 OTHER CIRCUITS

4-5-1 COMPANDER CIRCUIT (MAIN UNIT)
IC-F33GT/GS/F34GT/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 sec-
tion, and are then applied to the limiter section after being
passed through the high-pass filter. The filtered signals 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 sec-
tion 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
VR1 Com-
TXIN 3
(HPF) pressor
TXA1
VR3 RX
RXIN 23
(HPF) LPF
RXA1
SDEC 21
MTDT 10
MTCK 9
MDIR 14
MSCK 13
MSK
Control
MDIO 11
BPF
Register
MRDF 12
Pre-
emphasis
TX/RX
HPF De-scrambler
MSK
Modulator
MSK
Demodulator

4-6 PORT ALLOCATIONS

4-6-1 D/A CONVERTOR IC (IC12)
Pin Port
Number name
10 BAL
14 TLVA
15 RLVA
T1
22
23 T2
Limiter
Scrambler/
De-
emphasis
4 - 5
Description
Outputs the modulation balance level
control signal. The signal is applied to
the buffer amplifi er (IC24, pin 1).
Outputs the TX VCO lock voltage
control signal.
Outputs the RX VCO lock voltage
control signal.
Outputs the bandpass filter tuning
control signal . The output signal is
applied to the bandpass fi lters (D19,
D240).
• Outputs the bandpass filter tuning
control signal . The output signal is
applied to the bandpass fi lters (D14,
D15).
• Outputs the TX control signal . The
output signal is applied to the APC
amplifi er (IC2, pin 1).
7 MOD
Splatter VR2 SMF
18
Expander VR4
19
20 SIGNAL
RXA2