Frequency Synthesizer (Main Unit); Frequency Synthesizer Circuits; Ais Receive Circuits (Ais Unit: Ux-231); Nmea2000 Data Routing Circuits (Nmea2000 Unit: Uc-232) - Icom ic-m506 Service Manual

4-3 FREQUENCY SYNTHESIZER (MAIN UNIT)

• VCOs
TX VCO
The TX VCO (Q3, Q4 and D2–D4) generates both the TX
signal and 1st LO signal for CH70.
While receiving, the LO signal is applied to the 1st IF mixer
for CH70 (Q302), through the LO SW (D8) and LPF (L66, L65
and C393).
While transmitting, the LO signal is applied to the TX AMP
circuits, through the LO SW (D7).
RX VCO
The RX VCO (Q72 and D51–D53) generates the 1st LO sig-
nal for MAIN channels.
The LO signal is applied to the 1st IF mixer for MAIN chan-
nels (D202), through the LPF (L221, L222 and C262).
• PLL
TX VCO
A portion of VCO output signal is passed through two buffers
(Q5 and Q6), and then fed back to the PLL IC (IC101, pin 1),
through the ATT (R33–R35) and LPF (L8, C74 and C75).
RX VCO
A portion of VCO output signal is passed through two buf-
fers (Q74 and Q75), and then fed back to the PLL IC (IC101,
pin 16), through the ATT (R47–R49) and LPF (L6, C77 and
C78).
The PLL IC (IC101) phase-compares the outputs of the refer-
ence frequency oscillator (TCXO: X101) and VCO, and the
phase-difference is output as the charge pump current.
The current is passed though the loop fi lter (TX VCO: R1–R3,
C1–C3, and C10, RX VCO: R161, R171, C156–C158) to be
converted into the lock voltage that controls the oscillating
frequency of VCO.
When the oscillation frequency drifts, its phase changes from
that of the reference frequency, causing a lock voltage change
to compensate for the drift in the VCO oscillating frequency.

• FREQUENCY SYNTHESIZER CIRCUITS

Q72
IC301
Q74
D51-D53
LOOP
IF IC
RX VCO
BUFF
FIL
21.25MHz
IC101
BUFF
PLL IC
X101
BUFF
Q3,Q4
Q5
D2-D4
LOOP
TX VCO
BUFF
FIL
Q2 Q8
D1
MOD
From the TX AF SHIFT
circuits
D202
1st mixer(MAIN ch)
1st Lo frequency range:
125.900-133.125 MHz
[USA],[AUS]
125.850-133.275 MHz
Other than [USA],[AUS]
Q76 Q302
1st mixer(CH70)
BUFF
CH70 1st Lo frequency:
134.825 MHz
Q75
D7,D8
TX/RX
To the TX AMP
SW
circuits
Q7
Q6
BUFF
4-4 AIS RECEIVER (AIS UNIT: UX-231)
The RX signal from the RF AMP (Q101) is applied to the AIS
UNIT, through J5 on the MAIN UNIT of IC-M506.
The applied signal is passed through the SAW fi lter (FI1) and
applied to the 1st mixer (Q1), and mixed with the 123.175 MHz
1st LO signal, resulting in the 1st IF signal (38.85 MHz for
AIS 1, 38.8 MHz for AIS 2).
The 1st IF signal is applied to the IF ICs (IC1 for AIS 1, IC2 for
AIS 2), and mixed with the 2nd LO signal (38.4 MHz for AIS 1,
38.35 MHz for AIS 2), resulting in the 450 kHz 2nd IF signal.
The 2nd IF signal is passed through the 2nd IF fi lter (FI4 for
AIS 1, FI7 for AIS 2) to remove the sideband noise. The fi l-
tered signal is amplifi ed by the 2nd IF AMP, and demodulated
by the quadrature detector with discriminator (X2 for AIS 1,
X4 for AIS 2).
The demodulated AF signal is applied to the AIS baseband
processor (IC8). The processed AIS data is applied to the IC-
M506, through J5 on the MAIN UNIT of IC-M506.
• AIS RECEIVE CIRCUITS
FI1
Q1
SAW
BPF
Q2 Q3
X1
X3 AMP
TCXO
41.0583 MHz
IC6
X5
AMP X2
TCXO
19.200 MHz
IC8
Buffer
NMEA
Formter
UART
Buffer
4-5 NMEA2000 DATA ROUTING CIRCUITS
(NMEA2000 UNIT: UX-232)
The AIS and GPS position data from the external devices is
sent to the IC-M506, through the NMEA2000 network.
• NMEA2000 DATA ROUTUNG CIRCUITS
Q3 Q4
D1 IC3
CI-V
I C F 3 C L O N E
I/F
BUFF
IC1
NM2K DATA
X1
MAIN UNIT
4-4
FI4
CERAMIC
BPF
450 kHz
IC1
FI2,3 FL-470
XTAL
2NDIF
BPF AMP
38.850 MHz
RSSI
2ND LO
BRF
BUFF
38.400 MHz
FI7
CERAMIC
BPF
450 kHz
IC2
FI5,6 FL-473
XTAL
2NDIF
BPF
AMP
38.800 MHz
2ND LO
RSSI
BUFF
X3 38.350 MHz
HDLC NRZI GMSK
decode decode decode
MUX
HDLC NRZI GMSK
decode decode decode
IC5
IC6
CAN TX PHOTO
IC2
BUFF COUPLE
LEVEL
CONV
IC3
IC4
PHOTO CAN RX
COUPLE
BUFF
CONNECT UNIT
X2
FM
DET
X4
FM
DET
AMP
AMP
J1
1
2
2 1
3
5
4
3 4
5