Icom IC91AD User Manual
SERVICE
MANUAL
VHF/UHF FM TRANSCEIVER
VHF/UHF DIGITAL TRANSCEIVER
S-14230HZ-C1
May. 2006
INTRODUCTION
This service manual describes the latest service information
for the
VHF/UHF DIGITAL TRANSCEIVER
IC-91A VHF/UHF FM TRANSCEIVER, IC-91AD
at the time of
publication.
MODEL VERSION SYMBOL
IC-91AD
IC-91A
To upgrade quality, all electrical or mechanical parts and internal
circuits are subject to change without notice or obligation.
U.S.A. USA
Export EXP
U.S.A. USA-1
Taiwan TPE
Korea KOR
Australia AUS
Export
EXP-1
EXP-2
CAUTION
NEVER connect the transceiver to an AC outlet or to a DC
power supply 3.7 V. Such a connection could cause a fire or
electric hazard.
DO NOT expose the transceiver to rain, snow or any liquids.
DO NOT reverse the polarities of the power supply when
connecting the transceiver.
DO NOT apply an RF signal of more than 20 dBm (100 mW)
to the antenna connector. This could damage the transceiver's front end.
ORDERING PARTS
Be sure to include the following four points when ordering
replacement parts:
1. 10-digit Icom parts number
2. Component name and informations
3. Equipment model name and unit name
4. Quantity required
<SAMPLE ORDER>
5030002880 LCD HLM7972-010100 IC-91A Main unit 5 pieces
8810009560 Screw PH BT M2×6 ZK IC-91A Chassis 10 pieces
Addresses are provided on the inside back cover for your
convenience.
REPAIR NOTES
1. Make sure the problem is internal before disassembling the transceiver.
2. DO NOT open the transceiver until the transceiver is disconnected from its power source.
3. DO NOT force any of the variable components. Turn them slowly and smoothly.
4. DO NOT short any circuits or electronic parts. An insulated turning tool MUST be used for all adjustments.
5. DO NOT keep power ON for a long time when the transceiver is defective.
6. DO NOT transmit power into a signal generator or a sweep generator.
7. ALWAYS connect a 30 dB to 40 dB attenuator between the transceiver and a deviation meter or spectrum analyzer when
using such test equipment.
8. READ the instructions of test equipment thoroughly before connecting equipment to the transceiver.
Icom, Icom Inc. and logo are registered trademarks of Icom Incorporated (Japan) in the United States, the United
Kingdom, Germany, France, Spain, Russia and/or other countries.
TABLE OF CONTENTS
SECTION 1 SPECIFICATIONS
SECTION 2 INSIDE VIEWS
SECTION 3 DISASSEMBLY INSTRUCTIONS
SECTION 4 UT-121 UNINSTALLATION
SECTION 5 CIRCUIT DESCRIPITON
5-1 RECEIVER CIRCUITS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
5-2 TRANSMITTER CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2
5-3 PLL CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4
5-4 OTHER CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5
5-5 POWER SUPPLY CIRCUITS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5
5-6 PORT ALLOCATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5
SECTION 6 ADJUSTMENT PROCEDURES
6-1 PREPARATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
6-2 FREQUENCY AND TRANSMIT ADJUSTMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5
SECTION 7 PARTS LIST
SECTION 8 MECHANICAL PARTS AND DISASSEMBLY
SECTION 9 SEMICONDUCTOR INFORMATION
SECTION 10 BOARD LAYOUTS
10-1 LOGIC UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1
10-2 MAIN UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1
10-3 RF UNIT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1
10-4 UT-121 (Optional product; CODEC UNIT for IC-91AD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1
10-5 VCO UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1
SECTION 11 BLOCK DIAGRAM
SECTION 12 VOLTAGE DIAGRAMS
12-1 LOGIC UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1
12-2 MAIN UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-2
12-3 RF UNIT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-3
12-4 VCO UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-4
12-5 UT-121 (Optional product; CODEC UNIT for IC-91AD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-5
SECTION 1 SPECIFICATIONS
P
Y§
GENERAL
• Frequency coverange :
NOISRE6
5
!3
4
NAWIA
NAERO+
!
NAILARTSU
T
ROPX%
• Operating mode
DNAB!
X4n
n
n
n
n n
X4nn
X4n
DEETNARAU'nYLNOZ(-
n
X2n
X2n
X2n
n
n
: FM, AM*, WFM*, DV
X2
n
n
X2
X4
X2
B"
X4n
n
n
n
n
n
X4n n
n
n
n
DEETNARAU'nYLNOZ(-
DEETNARAU'nYLNOZ(-
†
Z(-TINU
DNA
n
n
n
(*RX only)
• Memory channels : 1304 channels
(Incl. 100 scan edges and 4 call ch.)
• Frequency stability : ±2.5 ppm
(–20°C to +60°C; –4°F to 140°F)
• Tuning steps : 5
‡
/6.25‡/8.33‡/9‡/10/12.5/15/20/
25/30/50/100/125 and 200 kHz
• Antenna impedance : 50 Ω (SMA type)
• Power supply : 10.0–16.0 V DC for external DC
power, or specifi ed Icom’s battery
pack
• Digital transmission speed : 4.8 kbps
• Voice coding speed : 2.4 kbps
†
†
• Current drain (at 7.4 V DC) :
TRANSMIT VHF High 2.1 A typ.
Low 0.8 A (approx.)
UHF High 2.2 A typ.
Low 0.8 A (approx.)
RECEIVE Stand-by 170 mA typ.
(dualwatch; FM/DV
Max. audio 340 mA typ.
(dualwatch; FM/DV
• Operating temp. range : –20°C to +60°C; –4°F to 140°F
• Dimensions
(projections not included)
• Weight (approx.)
:
58.4 (W) × 103 (H) × 34.2 (D) mm
2 9/32 (W) × 4 1/16 (H) × 1 11/32 (D) in
300 g; 10.6 oz
:
(antenna, BP-217 included)
TRANSMITTER
• Output power (at 7.4 V DC) : 5.0 W (High)
0.5 W (Low; aprrox.)
• Modulation system FM : Variable reactance frequency
modulation
†
DV
GMSK reactance frequency
modulation
• Maximum deviation : ±5.0 kHz (FM wide: approx.)
±2.5 kHz (FM narrow: approx.)
• Spurious emissions : Less than –60 dB
• Ext. mic. connector : 3-conductor 2.5 (d) mm; (
1
/10′′
)/2 kΩ
RECEIVER
• Receiving system :
FM/AM/DV
• Intermediate frequencies :
1st A band
2nd 450 kHz/13.35 MHz (WFM)
3rd 1.95 MHz (WFM only)
• Sensitivity : (except spurious points)
†
)
†
)
• Selectivity :
FM (Wide), AM More than 50 dB
FM (Narrow), DV
• Spurious image rejection :
• Audio output power
(at 7.4 V DC)
• Ext. speaker connector : 3-conductor 3.5 (d) mm; (
†
Double-conversion
superheterodyne system
WFM Triple-conversion
superheterodyne system
61.65/59.25 MHz (WFM)
B band
-
-
!
n
-
-&
6
46.35 MHz
n
-
nPYT6§Z(-
nPYT6§
n
&(
&(5
Z(-
KZ(K
UETAM!
Z(-
VE$Z(
BR
YLNODNA
YLNODNABRUETAM!
n
nPYT6§Z(-
n PYT6§Z(-
n
n
n PYT6§Z(-
n PYT6§
-
-
&7
nPYT6§Z(-
nPYT6§Z(-
nPYT6§Z(-
-
6$
RUE
TAM!
†
More than 45 dB
WFM More than 300 kHz/–3 dB
Less than 700 kHz/–20 dB
VHF More than 60 dB
UHF More than 50 dB
(IF; More than 60 dB)
: More than 200 mW
(at 10% distortion with an 8 Ω load)
.3"DDO-Z(K
PYT6§
PYT6§Z(-
P
YT6§Z(-
$!.)3"D
PYT
6§
PYT
6§
Z(-
PYT6§
P
YT6§Z(-
PYT
6§Z(-
Z(-
$!.)3"DVE$Z(KZ(K
o
2%"SPBK.0LATIGID
/8′′
PYT6§
)/8 Ω
SDNAB
1
†
Available for the IC-91AD or when UT-121 is installed into the IC-91A.
All stated specifi cations are subject to change without notice or obligation.
1 - 1
SECTION 2 INSIDE VIEWS
• LOGIC UNIT
Reference
frequency oscillator
(X1: CR-774)
RS-232C interface
(IC52: MAX3221IPWR)
CPU
HD64F2238RTF13V
(IC1:
Reset IC
(IC100: R1150H022D)
AF power amplifier
(IC550: NJM2070M)
ALC amplifier
(IC300: AN6123MS)
D/A converter
(IC303: M62364FP)
• UT-121
(Optional Product ; CODEC UNIT for IC-91AD)
(TOP VIEW)
GMSK modem IC
(IC202: CMX589AD5)
AMBE audio codec IC
(IC101: AMBE-2020)
)
Linear codec IC
(IC350: AD73311ARSZ)
• UT-121
(Optional Product ; CODEC UNIT for IC-91AD)
(BOTTOM VIEW)
Clock oscillator for
IC202
(X200: CR-821)
Clock oscillator for
IC101 / IC350
(X100: CR-820)
• MAIN UNIT (TOP VIEW) • MAIN UNIT (BOTTOM VIEW)
Mode switch
(IC700: CD4066)
2nd IF filters
(FI100, FI200: CFW450E)
A_BAND PLL IC
(IC400: MB15E03SLPFV1)
• RF UNIT (TOP VIEW) • RF UNIT (BOTTOM VIEW)
APC amplifier
(IC150: NJM3404)
TX power amplifier
(Q100: RD01MUS1)
VCO UNIT
A_BAND FM IF IC
(IC100: TA31136FNG)
B_BAND FM IF IC
(IC200: TA31136FNG)
A_BAND 2nd IF filter
(FI2: SFECV13.35MAS)
B_BAND 1st IF filter
(FI50: FL-335)
DC switch
Q1000: HAT1026
D1000: MA2S728
D1001: RB060
A_BAND 1st IF mixer
(IC900: µPC2757TB)
2 - 1
SECTION 3 DISASSEMBLY INSTRUCTIONS
• Removing the rear panel
1 Unscrew 2 screws A and remove the plate B.
2 Remove the CODEC unit (UT-121) if installed. (See the
page 4-1 “2” for uninstallation)
3 Unscrew 2 screws C and 2 screws D.
4 Disconnect the flat cable E from MAIN unit J702.
5 Remove the rear panel.
A
B
C
J702
CODEC unit
(UT-121)
D
Rear panel
• Removing the RF unit
1 Unsolder 2 points A.
2 Unsolder 3 points B and remove the shield plate C.
3 Unscrew 4 screws D and remove the RF unit from the
rear panel
D
C
D
B
RF unit
B
B
Rear panel
A
E
• Removing the MAIN unit
1 Unscrew the screw A and 2 screws B.
2 Unsolder 6 points C.
3 Remove the MAIN unit from the rear panel in the direction
of the arrow.
B
A
C
MAIN unit
Rear panel
A
• Removing the LOGIC unit
1 Unsolder 2 points A.
2 Unscrew 6 screws B and remove the LOGIC unit from the
front panel.
B
LOGIC unit
B
B
A
B
3 - 1
Front panel
SECTION 4 UT-121 UNINSTALLATION
RECOMMENDATION:
Critical technique is necessary for the UT-121 uninstallation, therefore, we recommend you to uninstall it at your
dealer or service center.
Turn the power OFF, and remove the battery pack.
q
Unscrew 2 screws to remove the unit cover.
w
2 screws
Unit cover
Insert the tweezers into the notches of the UT-121, and remove it as shown below.
e
Tweezers
Screw 2 screws to assemble the unit cover.
r
Unit cover
Notches
2 screws
(Top view)
UT-121
4 - 1
SECTION 5 CIRCUIT DESCRIPTION
5-1 RECEIVER CIRCUITS
This transceiver has two receiving lines called A_BAND and B_
BAND for dualwatch capability. A_BAND corresponds to FM/WFM/
AM mode receiving within 0.495–999 MHz range, and B_BAND
corresponds to FM/FM-N/AM/DV mode receiving within 118–174
MHz and 350–470 MHz ranges.
5-1-1 RF CIRCUITS (RF UNIT)
This transceiver has six RF circuits to provide wide receiving range.
The received signals from the antenna connector (CHASSIS; J1)
are applied to each RF circuit for the frequency coverage, and
amplified within the frequency coverage.
• While receiving 0.495–76 MHz
The received signals of 76 MHz and below are passed through the
low-pass filter (LPF; L200, L201, C201–C204) via the two LPFs
(L1–L3, C1–C6; L5–L7, C10–C14), attenuator (D10) and band
switch (D200).
The 0.495–30 MHz band signals are passed through the band
switch (D201), then applied to the RF amplifier (Q200) via the
low-pass filter (L202, L203, C205–C209). The 30–76 MHz band
signals are applied to the tuned RF amplifier (Q250, D252, D255)
via the band switch (D250).
The amplified signals are applied to the A_BAND 1st mixer (IC900,
pin 1) via the band switches (D203 or D256, D707).
- 0.495–76 MHz -
2 LPFs
to the A_BAND
1st mixer
(IC900, pin 1)
D707
D256
Q200
D203
D255
0.495
30
Q250
-
76 MHz
-
LPF
RF
amp.
Tuned RF amplifier
30 MHz
D201
D250
D252
0.495
-
LPF
LPF
76 MHz
• While receiving 76–118 MHz or 174–260 MHz
The 76–118 MHz band signals are passed through the two LPFs
(L1–L3, C1–C6; L5–L7, C10–C14), attenuator (D10) and low-pass
filter (L300, L301, C301–C305) via the band switch (D300).
The 174–260 MHz band signals are passed through the LPF (L1–
L3, C1–C6), HPF (L4, C7–C9), attenuator (D7) and high-pass filter
(HPF; L302, L303, C306–C310) via the band switch (D302).
The filtered signals are applied to the tuned RF amplifier (Q300,
Q301, D305, D307, D308) via the band switch (D301/D303).
The amplified signals are applied to the A_BAND 1st mixer (IC900,
pin 1) via the band switches (D311, D707).
D200
from the
antenna
D10
ATT
- 76–118 MHz or 174–260 MHz -
from the
antenna
LPFHPF
D707
to the A_BAND
1st mixer
(IC900, pin 1)
D303
D301
D311
174
76
-
260 MHz
LPF
-
118 MHz
D7
D302
D10
D300
D307, D308 Q300 D305Q301
Tuned RF amplifier
AT T
AT T
HPF
LPF
• While receiving 118–174 MHz
The 118–174 MHz band signals are passed through the two LPFs
(L1–L3, C1–C6; L5–L7, C10–C14) and attenuator (D10), then
applied to the RF amplifier (Q400) via the band switch (D400) and
bandpass filter (BPF; L400, L405, C400, C401).
The amplified signals are applied to the tuned RF amplifiers for A_
BAND (Q401, D401–D403) and B_BAND (Q450, D450–D452).
The amplified signals by Q401 are then applied to the A_BAND
1st mixer (IC900, pin 1) via the band switches (D405, D509).
The amplified signals by Q450 are then applied to the B_BAND
1st mixer (MAIN UNIT; IC50, pin 1) via the band switch (D454) and
J1001 (pin 15).
- 118–174 MHz -
from the
LPF
BPF
antenna
D400
to the A_BAND
1st mixer
(IC900, pin 1)
D509
to the B_BAND
1st mixer
(MAIN UNIT; IC50, pin 1)
D402, D403 Q401 D401
D405
D451, D452 Q450 D450
D454
Tuned RF amplifier 2 LPFs
Tuned RF amplifier
D10
ATT
Q400 118-174 MHz
RF
amp.
• While receiving 260–350 MHz or 470–600 MHz
The 260–350 MHz and 470–600 MHz band signals passed through
the LPF (L1–L3, C1–C6) and HPF (L4, C7–C9), then applied to
the tuned RF amplifier (Q500, Q501, D502, D505, D506) via the
attenuator (D7) and band switch (D500).
The amplified signals are applied to the A_BAND 1st mixer (IC900,
pin 1) via the band switches (D508, D509).
- 260–350 MHz or 470–600 MHz -
from the
antenna
D509
to the A_BAND
1st mixer
(IC900, pin 1)
D508
D7
D500
260
-
350 MHz, 470-600 MHz
D505, D506
Tuned RF amplifier
Q500 D502 Q501
HPF LPF ATT
5 - 1
• While receiving 350–470 MHz
The 350–470 MHz band signals are passed through the LPF (L1–
L3, C1–C6), HPF (L4, C7–C9) and attenuator (D7), then applied
to the RF amplifier (Q600) via the band switch (D600) and HPF
(L600, L601, L608, L611, C600–C602, C630, C631, C633).
While receiving 260–999 MHz band signals, the 1st LO signals are
generated at UHF BAND VCO (VCO UNIT; Q101, D101, D104).
If the receiving frequency is 600 MHz or higher, the VCO output
signal is doubled at the doubler circuit (RF UNIT; Q850) before
being applied to the 1st mixer (RF UNIT; IC900, pin 3).
The amplified signals are applied to the tuned RF amplifiers for
A_BAND (Q601, D601, D602, D604, D605) and B_BAND (Q651,
D650, D651, D653, D654).
The amplified signals by Q601 are then applied to the A_BAND
1st mixer (IC900, pin 1) via the band switch (D606).
The amplified signals by Q651 are then applied to the B_BAND
1st mixer (MAIN UNIT; IC50, pin 1) via the band switch (D655) and
J1001 (pin 15).
- 350–470 MHz -
from the
to the A_BAND
1st mixer
(IC900, pin 1)
D606
D655
to the
B_BAND 1st mixer
(MAIN UNIT; IC50, pin 1)
Tuned RF amplifier
D604, D605 Q601 D601, D602
Tuned RF amplifier
D653, D654 Q651 D650, D651
D7
ATT
Q600 350-470 MHz
RF
HPF
amp.
antenna
HPF LPF
D600
• While receiving 600–999 MHz
The 600–999 MHz band signals are passed through the HPF
(L8, L9, C16–C18) and band switch (D700), then applied to the
tuned RF amplifier (Q700, Q701, D702–D704) via the attenuator
(D701).
The amplified signals are applied to the A_BAND 1st mixer (IC900,
pin 1) via the band switch (D706).
- 600–999 MHz -
D701
D700
HPF ATT
from the
antenna
In FM/AM mode, the converted IF signal is applied to the 1st IF
filter (MAIN UNIT; FI1) via the mode switch (D2) to filter out the
unwanted signals, then applied to the IF amplifier (MAIN UNIT;
Q100).
In WFM mode, the converted IF signal is applied to the 1st IF
amplifier (MAIN UNIT; Q1) via the mode switch (D2). The amplified
1st IF signal is applied to the 2nd IF mixer (MAIN UNIT; Q2), and
converted into the 13.35 MHz IF signal by being mixed with the
45.95 MHz Lo signal. The converted IF signal is passed through
the IF filter (MAIN UNIT; FI2) to filter out the unwanted signal, then
applied to the IF amplifier (MAIN UNIT; Q100).
The amplified 1st or 2nd IF signal from the IF amplifier (MAIN
UNIT; Q100) is then applied to the A_BAND IF IC (MAIN UNIT;
IC100, pin 16).
• A_BAND 1st IF CIRCUIT
LO signals
from the VCOs
Q100
1st/2nd IF
signal to
the IF IC
(IC100, pin 16)
61.65 MHz
(FM/AM)
D3 D2
IF
amp.
13.35 MHz
(WFM)
BPF
FI2
BPF
FI1
Q1 Q2
IF
amp.
1st mixer
IC900
Received signals
from the
RF circuits
RF UNIT
MAIN UNIT
LO signal
from the TCXO (X450)
via Q450, Q451
• B_BAND (118–174 MHz, 350–470 MHz.)
The received signals from the RF circuits are applied to the
B_BAND 1st IF mixer (MAIN UNIT; IC50, pin 1), and converted
into the 46.35 MHz 1st IF signal by being mixed with 1st Local
Oscillator (LO) signals from the VCOs.
600
-
999 MHz
to the A_BAND
1st mixer
(IC900, pin 1)
D706
D703, D704
Tuned RF amplifier
Q700 D702 Q701
5-1-2 1ST IF CIRCUITS (RF AND MAIN UNITS)
The 1st IF circuits contain the 1st mixer, 1st IF amplifier and the
1st IF filter. The 1st IF mixer converts the received signals into a
fixed frequency of the 1st Intermediate Frequency (IF) signal. The
converted 1st IF signal is filtered at the 1st IF filters and amplified
at the IF amplifier.
• A_BAND (0.495–999 MHz)
The received signals from the RF circuits are applied to the A_
BAND 1st IF mixer (RF UNIT; IC900, pin 1), and converted into
the 61.65 MHz (FM/AM)/59.25 MHz (WFM) 1st IF signal by being
mixed with 1st Local Oscillator (LO) signals from the VCOs (VCO
UNIT).
While receiving 0.495–76 MHz band signals, the 1st LO signals
are generated at BC BAND VCO (VCO UNIT; Q1, D1, D3, D5, D6),
and for receiving 76–260 MHz band signals, the 1st LO signals are
generated at VHF BAND VCO (VCO UNIT; Q51, D51, D54).
While receiving 118–174 MHz band signals, the 1st LO signals are
generated at B_BAND VBVCO (MAIN UNIT; Q301, D300, D301),
and for receiving 350–470 MHz band signals, the 1st LO signals
are generated at B_BAND UBVCO (MAIN UNIT; Q351, D350,
D352).
The converted 1st IF signal is passed through the 1st IF filter
(MAIN UNIT; FI50) to filter out the unwanted signal, then applied to
the 1st IF amplifier (MAIN UNIT; Q200). The amplified 1st IF signal
is then applied to the B_BAND IF IC (MAIN UNIT; IC200, pin 16).
• B_BAND 1st IF CIRCUIT
Q200
IF
1st IF signal
to the IF IC
(IC200, pin 16)
amp.
46.35 MHz
BPF
FI50
LO signals
from the VCOs
1st mixer
IC50
Received signals
from the
RF circuits
MAIN UNIT
5 - 2
5-1-3 2ND IF AND DEMODULATOR CIRCUITS
(MAIN UNIT)
The 1st IF signal is converted into the 2nd IF signal and
demodulated in the IF IC. The IF IC contains 2nd mixer, limiter
amplifier, quadrature detector, etc. in its package.
5-1-3-2 DEMODULATOR CIRCUITS
• FM/WFM mode
The amplified IF signal from the limiter amplifier in the IF IC is
FM-demodulated at the quadrature detector (IC100, pins, 10, 11,
X100) and output from pin 9. The demodulated AF signals are
applied to the AF amplifier circuits.
5-1-3-1 2ND IF CIRCUITS
- A_BAND (0.495–999 MHz) -
• FM/AM mode
The 1st IF signal from the IF amplifier (Q100) is applied to the 2nd
mixer in the A_BAND IF IC (IC100, pin 16), and converted into the
450 kHz 2nd IF signal by being mixed with the 61.2 MHz 2nd LO
signal from the reference frequency oscillator (X450) quadrupled
by the quadruplicater (Q452).
The converted 2nd IF signal is output from pin 3, and passed
through the 2nd IF filter (FI100) via the mode switch (D102) to
suppress sideband noise.
In FM mode, the filtered 2nd IF signal is applied to the limiter
amplifier (IC100, pin 5) via the mode switch (D103).
In AM mode, the filtered 2nd IF signal is applied to the IF amplifier
(Q103) via the mode switch (D103).
• WFM mode
The 2nd IF signal from the IF amplifier (Q100) is applied to the 3rd
mixer in the A_BAND IF IC (IC100, pin 16), and converted into the
1.95 MHz 3rd IF signal by being mixed with the 15.3 MHz 2nd LO
signal from the reference frequency oscillator (X450).
The converted IF signal is output from pin 3, and applied to the
limiter amplifier (IC100, pin 5) via the mode switches (D102,
D103).
• AM mode
The amplified IF signal from the IF amplifier (Q103) is applied to
the AM demodulator (Q104, Q105).
The demodulated AF signals are applied to the AF amplifier
circuits.
- B_BAND (118–174 MHz, 350–470 MHz) -
The 1st IF signal from the 1st IF amplifier (Q200) is applied to the
2nd mixer in the B_BAND IF IC (IC200, pin 16), and converted into
the 2nd IF signal by being mixed with the 2nd LO signal from the
reference frequency oscillator (X450) tripled by the tripler (Q451).
The converted 2nd IF signal is output from pin 3, and passed
through the 2nd IF filter (FM/AM mode: FI200; FM-N mode: FI201)
via the mode switch (D202) to suppress sideband noise.
• FM/FM-N mode
The filtered 2nd IF signal is applied to the limiter amplifier in the
B_BAND IF IC (IC200, pin 5) via the mode switch (D203). The
amplified 2nd IF signal is FM-demodulated at the quadrature
detector (IC200, pins, 10, 11, X200) and output from pin 9. The
demodulated AF signals are applied to the AF amplifier circuits.
• AM mode
The 2nd IF signal is passed through the FI200 and applied to the
AM demodulator circuit (Q203, Q204) via the IF amplifier (Q202).
The demodulated AF signals are applied to the AF amplifier
circuits.
• A_BAND 2ND IF AND DEMODULATOR CIRCUITS
Limitter
Amplifier
11 10
Q103
MAINR3A
2nd IF signal to the AM demodulator (Q104, Q105)
Quadrature
Detector
9
FM-demodulated signals
to the AF amplifier circuits
X100
L101
8
Noise
Amplifier
D103
7 3 5
(+3V)
Mode switch
Q101, Q102
(FM/AM)
BPF
FI100
R117
RSSI
D102
Noise
Detector
13 12
15.3/61.2 MHz
2nd LO signal
2
16
“ANOIS” signal to the CPU (LOGIC UNIT; IC1, pin 26)
“S-LV” signal to the CPU (LOGIC UNIT; IC1, pin 48)
D450
Q450
X4
Q452
A_BAND IF IC (IC100)
1st IF signal from the IF amplifier (Q100)
TCXO
X450
5 - 3
• B_BAND 2ND IF AND DEMODULATOR CIRCUITS
2nd IF signal to the AM demodulator (Q203, Q204)
8
Q202
7 3 5
D203
(FM/AM)
BPF
FI200
BPF
FI201
(FM-N)
D202
45.9 MHz
2nd LO signal
2
X3
Q451
Q450
TCXO
X450
Noise
Amplifier
Limitter
Quadrature
Detector
9
FM-demodulated signals
to the AF circuits
X200
Mode switch
Q201
Amplifier
11 10
MAINR3B
(+3V)
W/N
5-1-4 AF AMPLIFIER CIRCUITS
(MAIN AND LOGIC UNITS)
The demodulated AF signals from the demodulator circuits are
amplified and filtered in AF amplifier circuits.
- A_BAND -
• FM/WFM mode
The demodulated AF signals from the A_BAND IF IC (MAIN UNIT;
IC100, pin 9) are applied to the mode switch (MAIN UNIT; IC500,
pins 1, 2) and then passed through the AF filter (MAIN UNIT;
Q550, Q552).
• AM mode
The demodulated AF signals from the AM-demodulator circuit
(MAIN UNIT; Q104, Q105) are applied to the AF switch (MAIN
UNIT; D105) and then passed through the AF filter (MAIN UNIT;
Q550, Q552).
- B_BAND -
• FM/FM-N mode
The demodulated AF signals from the B_BAND IF IC (MAIN UNIT;
IC200, pin 9) are applied to the mode switches (MAIN UNIT; IC500,
pins 10, 11, IC700, pins 11, 10) and then passed through the AF
filter circuit (MAIN UNIT; IC501 pins 1, 2; 6, 7).
Noise
Detector
RSSI
B_BAND IF IC (IC200)
13 12
16
1st IF signal from the 1st IF amplifier (Q200)
“BNOIS” signal to the CPU (LOGIC UNIT; IC1, pin 28)
“BRSSI” signal to the CPU (LOGIC UNIT; IC1, pin 46)
• AM mode
The demodulated AF signals from the AM-demodulator circuit
(MAIN UNIT; Q203, Q204) are applied to the AF (MAIN UNIT;
D205) and mode switches (MAIN UNIT; IC700, pins 10, 11) and
then passed through the AF filter (MAIN UNIT; IC501 pins 1, 2;
6, 7).
The filtered AF signals are applied to the D/A converter (LOGIC
UNIT; IC303 for A_BAND; pins 21, 22; 23, 24/for B_BAND;
pins 13–16) and level adjusted. The level adjusted AF signals
are applied to the AF power amplifier (LOGIC UNIT; IC550, pin
2). The power amplified AF signals are then output from pin 6,
and applied to the internal speaker (CHASSIS; SP1) via [SP]
connector (MAIN UNIT; J700).
5-1-5 AGC CIRCUIT (MAIN AND RF UNITS)
A portion of the AM-demodulated signals are converted into DC
voltage by AGC (Automatic Gain Control) detector (MAIN UNIT;
Q104; A_BAND/Q203; B_BAND), and fed back to the IF and RF
circuits as the AGC signal.
• AF CIRCUITS
from the AM
demodulator
circuit (Q104, Q105)
from the A_BAND
IF IC (IC100, pin 9)
from the B_BAND
IF IC (IC200, pin 9)
from the AM
demodulator
circuit (Q203, Q204)
MAIN UNIT LOGIC UNIT
Q550
FM/AM
IC500
1 2
3 4
10 11
IC700
11 10 2 7
AF
filter
WFM
Q552
AF
filter
IC501
AF
filter
5 - 4
IC303
D/A
IC550
23
15
21
13
converter
AF
2 6
power
amp.
Speaker
[SP] jack
The AGC signal controls the bias of the IF amplifiers (MAIN UNIT;
Q100, Q103/Q200, Q202) and RF amplifiers (RF UNIT; Q200,
Q250, Q300, Q301, Q401, Q500, Q501, Q601/Q700, Q701,
Q450, Q651) according to the received signal strength to prevent
audio distortion and stabilize the demodulated AF signal level.
The IDC limits the level of the amplitude of MIC signals to prevent
over deviation. The limited MIC signals are output from pin 7 and
passed through the splatter filter (IC302, pins 8, 9).
The splatter filter suppresses 3 kHz and higher audio
components.
5-1-6 SQUELCH CIRCUITS (MAIN AND LOGIC
UNITS)
• NOISE SQUELCH
The noise squelch mutes the AF output signals when no RF
signals are received. By detecting noise components in the
demodulated AF signals, the squelch circuit toggles the AF power
amplifier ON and OFF.
A portion of the FM-demodulated AF signals from the IF IC (MAIN
UNIT; IC100/IC200 (A_BAND/B_BAND), pin 9) is passed through
the noise filter (MAIN UNIT; IC100/IC200, pins 7, 8, R109–R113,
C118–C122/R212–R216, C218–C222). The filtered noise signals
are then applied to the noise amplifier in the IF IC to be amplified
the noise components only.
The amplified noise components are converted into the pulsetype signal at the noise detector section, and output from pin 13
as the noise signal (A_BAND: “ANOIS”/B_BAND: “BNOIS”). The
noise signal is applied to the CPU (LOGIC UNIT; IC1, pin 26/28),
then the CPU outputs “AFON” signal from pin 97 according to
the noise detection signal level to toggle the AF power amplifier
regulator (LOGIC UNIT; Q105, Q106) ON and OFF.
• TONE SQUELCH
The tone squelch detects the tone signal in the demodulated AF
signals, and opens the squelch only when matched subaudible
tone frequency is detected in the received signal.
While the tone squelch is in use, and the received signal contains
no sub-audible tone signal or mismatched tone frequency, the
tone squelch mutes the AF signals even if the noise squelch is
open.
A portion of the demodulated AF signals from the IF IC (MAIN
UNIT; IC100/IC200, pin 9) are passed through the two-staged
CTCSS/DTCS filter (MAIN UNIT; IC150/IC250, pins 3, 1 and pins
5, 7) via the mode switch (MAIN UNIT; IC500, pins 1, 2/10, 11)
to suppress unwanted voice signals. The filtered CTCSS/DTCS
signals (A_BAND: “ATONE”/B_BAND: “BTONE”) are applied
to the CPU (LOGIC UNIT; IC1, pin 49/45) via the tone selector
(MAIN UNIT; IC703, pins 3, 4/10, 11).
The CPU decodes the CTCSS/DTCS signal, and outputs “AFON”
signal from pin 97 according to the set CTCSS/DTCS signal to
toggle the AF power regulator (LOGIC UNIT; Q105, Q106) ON
and OFF.
5-2 TRANSMITTER CIRCUITS
5-2-1 MICROPHONE AMPLIFIER CIRCUIT
(LOGIC UNIT)
The microphone amplifier circuit contains AF amplifier, IDC,
splatter filter, etc. The AF signals from the microphone (thereafter,
it is called “MIC signals”) are filtered and level-adjusted at this
circuit.
MIC signals from the microphone (MC300) are applied to the MIC
amplifier (Q302), then the amplified MIC signals are applied to
the mode switch (IC301, pin 1). In FM mode, the MIC signals are
output from pin 6 and applied to the IDC (Instantaneous Deviation
Control; IC302, pin 5).
In DV mode
the IDC (IC302, pin 5) via the ALC amplifier (IC300, pins 3, 5).
†
, the MIC signals are output from pin 7 and applied to
The filtered MIC signals are applied to the D/A converter (IC303,
pin 1) via the mode switch (IC304, pins 10, 11). The D/A converter
(IC303) adjusts the deviation according to “DATA” signal from the
CPU (IC1, pin 30).
The level adjusted MIC signals are output from pin 2 and then
applied to the modulation circuit (VCO UNIT; D55 or D100) to
modulate the VCO oscillating signal.
• MICROPHONE AMPLIFIER CIRCUIT
Microphone
Q302
MIC
IC301
1
3 5
DV mode* onry
Mode
switch
7
IC300
ALC
6
IC304
11 10
IC302
IDC
SPLATTER
9
7
1 2
converter
IC303
D/A
8 5
to the
VCO
5-2-2 MODULATION CIRCUIT (VCO UNIT)
The modulation circuit modulates the VCO oscillating signal with
the AF signals from the microphone and the tone signals from the
CPU.
• MICROPHONE SIGNALS
The level adjusted MIC signals from the D/A converter (LOGIC
UNIT; IC303, pin 2) are applied to the D55 (in transmitting on 144
MHz band) or D100 (in transmitting on 430 MHz band) to modulate
the VCO oscillating signal by changing the reactance of D55 or
D100. The modulated VCO output signal is buffer-amplified by
Q200 and Q201, then applied to the transmit amplifiers via TX/RX
switch (RF UNIT; D100) and amplifier (RF UNIT; IC100, pins 1, 4),
as a transmit signal.
• TONE SIGNALS
The CTCSS and DTCS signals are generated by the CPU (LOGIC
UNIT; IC1) and output from pin 43.
The CTCSS/DTCS signals are passed through the tone filter
(Q307, R338–R340, C339, C340). The filtered tone signals are
mixed with the MIC signal coving from the IDC amplifier (LOGIC
UNIT; IC302 pin 7), then applied to the modulation circuit via the
the splatter filter, mode switch and D/A converter.
The CTCSS/DTCS signals are passed through the tone filter
(Q307, R338–R340, C339, C340). The filtered tone signals are
mixed with the MIC signals come from the IDC amplifier (LOGIC
UNIT; IC302, pin 7), then applied to the modulation circuit (D55
or D100) via the splatter filter (LOGIC UNIT; IC302, pins 9, 8),
mode switch (LOGIC UNIT; IC304, pins 11, 10) and D/A converter
(LOGIC UNIT; IC303, pins 4, 3).
5-2-3 TRANSMIT AMPLIFIERS (RF UNIT)
The VCO output signal is amplified to transmit output power level
by the transmit amplifiers.
The VCO output signal from the amplifier (IC100) is applied to the
pre-driver (Q102), driver (Q101) and power (Q100) amplifiers in
sequence to be amplified to the transmit output power level. The
power amplified transmit signal is passed through the antenna
switching circuit and transmit filters.
†
Available for IC-91AD or when the optional UT-121 is installed into IC-91A.
5 - 5
5-2-4 APC CIRCUIT (RF UNIT)
The APC (Automatic Power Control) circuit stabilizes transmit output
power and controls it High or Low. The APC of this transceiver is a
current monitoring type that detects the transmit signal current of
the transmit amplifiers and controls the transmit output power.
While transmitting, the voltagedrop in R161 is detected by the
current detection circuit (Q150) and applied to the APC controller
(IC150, pin 6). Also, “PSET” signal (power setting reference voltage)
from the D/A converter (IC950, pin 19) is applied to another input
(pin 5).
Then the voltage difference between pins 5 and 6 is output from
pin 7, and the transmit output power is controlled by varying of the
gate voltage of the power amplifier (Q100).
5-3 PLL CIRCUITS
5-3-1 VCO CIRCUITS (VCO UNIT AND MAIN UNIT)
This transceiver has 5 VCOs; BC BAND VCO, VHF BAND VCO,
UHF BAND VCO, B_BAND VBVCO and B_BAND UBVCO. The
BC BAND VCO, B_BAND VBVCO and B_BAND UBVCO oscillate
the 1st LO signals. The VHF BAND VCO and UHF BAND VCO
oscillate both transmit output signal and 1st LO signals.
- A_BAND -
• BC BAND VCO
The BC BAND VCO (VCO UNIT; Q1, D1, D3, D5, D6) generates
the 1st LO signals for receiving 0.495–76 MHz signals. The output
signals are amplified at the buffer amplifiers (VCO UNIT; Q200,
Q201), then applied to the 1st mixer (RF UNIT; IC900, pin 3) via
TX/RX switch (RF UNIT; D850).
When the transmit output power is set to Low, the driver gate
voltage “DSET” is controlled at the same time as the power setting
reference voltage “PSET” and the dynamic range of the power
control is ensured. Thus, the APC circuit maintains a constant
transmit output power.
• APC CIRCUIT
VCC
from the
pre-driver
(Q102)
DSET
PSET
R161
Current
detection
Q150
3
5
controller
6
IC150
APC
Q101 Q100
Driver
amp.
1
7
Power
amp.
to the
transmit
filters
5-2-5 TRANSMIT FILTERS (RF UNIT)
The power amplified transmit signal from the power amplifier is
filtered at the transmit filters. The transmit filters prevent unwanted
RF signals being emitted to the air.
While transmitting in 144 MHz band, the power amplified transmit
signal is passed through the LPF (L102, L103, C106, C107), antenna
switch (D8) and two LPFs (L5–L7, C10–C14; L1–L3, C1–C6) before
being applied to the antenna connector (CHASSIS; J1).
• 144 MHz
from the
power amplifier
(Q100)
LPF
D8
ANT
SW
LPF
LPF
to the antenna
• VHF BAND VCO
The VHF BAND VCO (VCO UNIT; Q51, D51, D54, D55) generates
both of transmit output signal for 144 MHz band and 1st LO signals
for receiving 76–260 MHz.
While receiving, the VCO oscillates the 1st LO frequency, and the
output signals are amplified at the buffer amplifiers (VCO UNIT;
Q200, Q201). The buffer-amplified signals are applied to the 1st
mixer (RF UNIT; IC900, pin 3) via TX/RX switch (RF UNIT; D850).
While transmitting, the VCO oscillates the transmit frequency,
and the output signal is amplified at the buffer amplifiers (VCO
UNIT; Q200, Q201). The buffer-amplified signals are applied to the
transmit amplifiers via TX/RX switch (RF UNIT; D100).
• UHF BAND VCO
The UHF BAND VCO (Q101, D100, D101, D104) generates both
of the transmit output signal for 430 MHz band and 1st LO signals
for receiving 260–999 MHz.
While receiving, the VCO oscillates the 1st LO frequency, and the
output signals are amplified by the buffer amplifiers (VCO UNIT;
Q200, Q201). If the receiving frequency is 600 MHz and below,
the buffer-amplified signals are applied to the 1st mixer (RF UNIT;
IC900, pin 3) via TX/RX switch (RF UNIT; D850). If the receiving
frequency is 600 MHz and higher, the buffer-amplified signals are
applied to the doubler circuit (RF UNIT; Q850), then the doubled
signals are applied to the 1st mixer (RF UNIT; IC900, pin 3).
While transmitting, the VCO oscillates the transmit frequency, and
the output signal is amplified at the buffer amplifiers (VCO UNIT;
Q200, Q201), then applied to the transmit amplifiers via TX/RX
switch (RF UNIT; D100).
A portion of the VCO output signals generated at BC/VHF/UHF
BAND VCO are applied to the PLL IC (RF UNIT; IC800, pin 4) via
buffer amplifiers (VCO UNIT; Q200, Q202) for comparison signal.
While transmitting in 430 MHz band, the power amplified transmit
signal is passed through the HPF (L100, L101, C100–C103),
antenna switch (D1, D2), HPF (L4, C7–C9) and LPF (L1–L3, C1–
C6) before being applied to the antenna connector (CHASSIS; J1).
• 430 MHz
from the
power amplifier
(Q100)
HPF
D1, D2
ANT
SW
HPF
LPF
to the antenna
5 - 6
- B_BAND -
• VBVCO
The VBVCO (MAIN UNIT; Q301, D300, D301) generates the 1st
LO signals for receiving 118–174 MHz signals. The output signals
are amplified at the buffer amplifier (MAIN UNIT; Q353), then
applied to the 1st mixer (MAIN UNIT; IC50, pin 3).
• UBVCO
The UBVCO (MAIN UNIT; Q351, D350, D352) generates the 1st
LO signals for receiving 350–470 MHz signals. The output signals
are amplified at the buffer amplifier (MAIN UNIT; Q353), then
applied to the 1st mixer (MAIN UNIT; IC50, pin 3).
A portion of the VCO output signals generated at VBVCO/UBVCO
are applied to the PLL IC (MAIN UNIT; IC400, pin 8) via buffer
amplifier (MAIN UNIT; Q353) for comparison signal.
5-3-2 PLL CIRCUITS (RF AND MAIN UNITS)
The PLL circuit provides stable oscillation of the transmit frequency
and receive 1st LO frequency. The PLL circuit compares the phase
of the divided VCO frequency with the reference frequency. The
PLL output frequency is controlled by the divided ratio (N-data)
from the CPU.
• A_BAND PLL CIRCUIT
The buffer amplified signals from the buffer amplifier (VCO UNIT;
Q202) are applied to the PLL IC (RF UNIT; IC800, pin 4). The applied
signals are divided at the prescaler and OSC counter according to
the “PLLDATA” signal from the CPU (LOGIC UNIT; IC1, pin 94).
The divided signal is phasecompared with the reference frequency
at the phase detector.
• A_BAND PLL AND VCO CIRCUITS
The phase difference is output from pin 2 as a pulse type signal
after being passed through the internal charge pump. The output
signal is applied to the BC/VHF/UHF BAND VCOs (VCO UNIT)
after being converted into the DC voltage (lock voltage) at the loop
filter (RF UNIT; C820–C823, R806–R808).
The lock voltage for BC BAND VCO (“BCLV”) from the loop filter
is applied to the VCO (VCO UNIT) via R815 and pin 1 of J800
(RF UNIT). The lock voltage for VHF BAND VCO (“VLV”) from the
loop filter is applied to the VCO (VCO UNIT) via R811 and pin 6
of J800 (RF UNIT). The lock voltage for UHF BAND VCO (“ULV”)
from the loop filter is applied to the VCO (VCO UNIT) via pin 16 of
J800 (RF UNIT).
VCO BOARD
BC BAND VCO
Q1,D1,D3,D5,D6
BCLV VLV
ULV
R815 R811
“UNLK” signal to the CPU
(LOGIC UNIT; IC1, pin 92)
Loop
filter
UHF BAND VCO
Q101,D100,D101,D104
VHF BAND VCO
Q51,D51,D54,D55
PLL IC (IC800)
Charge
2
Pump
9
Reference
Counter
Phase
Detector
6
Buffer
amp.
Q200
OSC
Counter
Input Register
Reference frequency
signal 15.3 MHz
from the TCXO
(MAIN UNIT; X450)
LO
amp.
Q201
Buffer
amp.
Q202
Pre-
scaler
LOOUT
PLLOUT
4
10
12
13
Doubler
×2
Q850
D850
“CK”
“PLLDATA”
“APLLSTB”
D100
PLL IC control signals
from the CPU (LOGIC UNIT; IC1)
4 1
IC100
transmit signal
to the transmit
amplifiers
1st LO signals to the
1st mixer (IC900, pin 3)
RF UNIT
5 - 7
• B_BAND PLL CIRCUIT
The buffer amplified signals from the buffer amplifier (MAIN UNIT;
Q353) are applied to the PLL IC (MAIN UNIT; IC400, pin 8). The
applied signals are divided at the prescaler and OSC counter
according to the “PLLDATA” signal from the CPU (LOGIC UNIT;
IC1, pin 94). The divided signal is phasecompared with the
reference frequency at the phase detector.
The phase difference is output from pin 5 as a pulse type signal
after being passed through the charge pump. The output signal is
• B_BAND PLL AND VCO CIRCUITS
VBVCO
Q301,D300,D301
UBVCO
applied to the B_BAND VBVCO/UBVCO (MAIN UNIT) after being
converted into the DC voltage (lock voltage) at the loop filter (MAIN
UNIT; R404–R406, C410–C412, C414). The lock voltage from the
loop filter is applied to each VCO.
If the oscillated signal drifts, its phase changes from that of the
reference frequency, causing a lock voltage change to compensate
for the drift in the oscillated frequency.
Buffer
amp.
Q353
1st LO signals to the
1st mixer (IC50, pin 3)
Q351,D350,D352
PLL IC (IC400)
Loop filter
“BPS” signal to the CPU
(LOGIC UNIT; IC1, pin 93)
15.3 MHz “REF”
signal to the PLL IC
(RF UNIT; IC800, pin 6)
45.9 MHz
2nd LO signal
15.3/61.2 MHz
2nd LO signal
D450
×3
Q451
Q452
×4
5
12
Charge
Buffer
amp.
Q450
Pump
Phase
Detector
Reference
Counter
1
5-4 DIGITAL CIRCUITS
5-4-1 LINER CODEC
(UT-121; CODEC UNIT for IC-91AD)
IC350 is a liner codec IC which converts transmitting AF signals
from the LOGIC unit into digital signals, and outputs them to the
audio codec IC (IC101) as 16-bit audio data.
IC350 also converts the 16-bit audio data from the audio codec IC
(IC101) into analog signals, and outputs them to the LOGIC unit as
the receiving AF signals.
OSC
Counter
Input Register
TCXO
X450
15.3 MHz
Pre-
scaler
5
9
10
11
“CK”
“PLLDATA”
“BPLSTB”
PLL IC control signals
from the CPU
(LOGIC UNIT; IC1)
MAIN UNIT
5-4-2 AUDIO CODEC
(UT-121; CODEC UNIT for IC-91AD)
IC101 is an AMBE audio codec IC. While receiving, digital signals
from the LOGIC unit are expansion decoded in IC101, and output
to the liner codec IC (IC350).
While transmitting, 16-bit audio data from the liner codec IC (IC350)
are compression coded in IC101, and output to the LOGIC unit.
5-4-3 MODEM (UT-121; CODEC UNIT for IC-91AD)
IC202 is a GMSK modem IC. While receiving, demodulated AF
signals from the MAIN unit are output to the LOGIC unit as digital
signals synchronized with clock signal.
While transmitting, digital signals from the LOGIC unit are converted
into GMSK base-band signal, and output to the LOGIC unit.
5 - 8
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