4-5 OTHER CIRCUITS
4-5-1 COMPANDER CIRCUIT (MAIN UNIT)
IC-F1700/F1800 series have compander circuit which can
improve S/N ratio and become wide dynamic range. The
circuit is composed in the base band IC (IC2).
(1) IN CASE OF RECEIVING
The demodulated AF signals from the FM IF IC (IC12, pin 9)
are applied to the amplifi er section in base band IC (IC2, pin
23), and then pass through the low-pass and high-pass fi lter
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 output signals from the base band IC (IC2, pin20)
is applied to the AF amplifier circuit after amplified at the
amplifi er section.
(2) IN CASE OF TRANSMITTING
The audio signals from the microphone are applied to the
base band IC (IC2, pin 3) via microphone amplifi er (FRONT
UNIT; IC5). The signals are amplifi ed at the amplifi er 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 fi lter.
The filtered signals pass through the splatter filter section,
and are then applied to the modulation circuit (D12) via the
FM/PM switch (IC43, pins12–14) and D/A converter (IC8,
pins 2, 3).
4-5-2 DIGITAL MODE CIRCUIT (IC-F1721D/F1821D only)
(1) IN CASE OF RECEIVING
Output signal from the FM IF IC (IC12, pin 11) is applied to
the IF amplifi er (Q3), and is then amplifi ed at the IF amplifi er
(IC15, pins, 1, 4) after pass through the bandpass fi lter (FI3).
The amplifi ed signal is applied to the DSP IC (IC41) via the
A/D converter (IC16, pin 3). The signal is processed at the
DSP IC (IC41) and is then applied to the LINER CODEC IC
(IC18, pin 16) to convert into an analog audio signal.
Output signal from the LINER CODEC IC (IC18) is applied
to the base band IC (IC2, pin 23) same as analog received
signal via the DA switch (IC42, pins 1, 15).
(2) IN CASE OF TRANSMITTING
Output signal from the base band IC (IC2, pin 7) is ampli-
fi ed at the MOD amplifi er (IC44) and is then applied to the
CODEC IC to convert to into a digital signal. The signal is
processed at the DSP IC (IC41) and the DIGITAL CPU (IC20),
and then applied to the low-pass fi lter (IC13, pins 1–3) after
amplifi ed at IC13 (IC13, pins 5, 7).
The signal is applied to the FM/PM switch (IC43, pins,
12–14) same as an analog transmit signal via the DA switch
(IC42, pins 13, 14).
4 - 5
Scrambler/
De-scrambler
TX/RX
HPF
Pre-
emphasis
Limiter
Splatter
VR2
Expander
VR4
RXA2
SMF
De-
emphasis
Com-
pressor
VR1
(HPF)
RX
LPF
VR3
(HPF)
7 MOD
18
19
20 SIGNAL
3
TXIN
23
RXIN
21
SDEC
10
14
MDIR
9
MTDT
MTCK
13
MSCK
11
MDIO
12
MRDF
MSK
Modulator
MSK
Demodulator
MSK
BPF
Control
Register
TXA1
RXA1
BPF
From FM IF IC
(IC12, pin 11)
To AF amplifier
ciruit
From
MIC amplifier
(FRONT UNIT; IC15)
To FM/PM SW
(IC43, pin 11)
DIGITAL
CPU
LPF
DA SW
AMP
AMP
AMP
AMP
Q3
IC42
IC13
RECEIVED SIGNAL
FI3
IC13
IC15
IC16
IC20
IC41
IC18
IC44
IC42
IC2
A/D
LINER
CODEC
IC
BASE
BAND
IC
DA SW
DSP
IC
TRANSMIT SIGNAL
• DIGITAL MODE CIRCUITS
• BASE BAND IC BLOCK DIAGRAM