Transmit Circuits; Frequency Synthesizer Circuits; Tx Af Circuit; Voltage Block Diagram - Icom IC-F1000 Service Manual

4-2 TRANSMIT CIRCUITS

TX AF CIRCUIT

The audio signal from the internal or external microphone
(MIC signal) is passed through the MIC gain SW (IC2) and
applied to the baseband IC (IC4).
The processed AF signal is passed through the AF
SW (IC2) and LPF (IC11), and then applied to the D/A
converter (IC10), which adjusts its level (=deviation). The
level-adjusted MIC signal is applied to the TX VCO as the
modulation signal.
• TX AF CIRCUIT
LIMIT
SPLT HPF
EMPH
AMP
IC2
IC11
IC10
AF
SW
LPF
MOD
To the modulation circuit
MODULATION CIRCUIT
The modulation signal from the TX AF circuits is applied
to D13 of the TX VCO (Q27, D11 to D13 and D33). The
frequency-modulated signal from is amplified by two buffers
(Q30 and Q31), and then applied to the TX AMP circuit,
through the TX/RX SW (D16).
• MODULATION CIRCUIT
Q30 Q31
TX VCO
Q27, BUFF BUFF
D11,D12,D33
D13
FREQUENCY
MODULATION
From the TX AF circuits
TX AMP CIRCUIT
The buffer amplified signal from the TX/RX SW (D16)
is sequentially amplified by the pre-AMP (Q34), drive
AMP (Q36) and power AMP (Q38). The power amplified TX
signal is passed through the antenna SW (D19) and LPF
(L29 to L31, C333, C347 to C350, C352 and C403), and
then applied to the antenna.
APC CIRCUITS
At the TX output power detector, the RF signal at the LPF
(L26, C303, C330, C353 and C355) is rectified by the
diodes (D22 and D23), and it is used as the TX power sens-
ing voltage.
The voltage is applied to the APC AMP (IC17), and the
output voltage controls the bias voltages of the drive AMP
(Q36) and power AMP (Q38) to keep the TX output power
constant.
• TX AMPLIFIERS AND APC CIRCUIT
Q34 Q36
From the
TX VCO
PRE
DRIVE
AMP
AM P
IC4
IC2
MIC
AMP
COMP
GAIN
D16
To the TX AMP circuits
TX/RX
SW
D19,D27
Q38
ANT
PWR
LPF
AM P
SW
IC17
APC
PWR
D22,D23
AMP
DET
To the RX circuits

4-3 FREQUENCY SYNTHESIZER CIRCUITS

The RX VCO is composed of Q25, D9, D10 and D32. The
output signal is amplified by two buffers (Q31 and Q31) and
applied to the 1st IF mixer (Q37), through the LO SW (D17)
and LO filter (LPF*: L41, C296 and C441, or HPF**: L21,
L42 and C293).
The TX VCO is composed of Q27, D11 to D13 and D33.
The output signal is amplified by two buffers (Q30 and Q31)
and applied to the pre-AMP (Q34), through the LO SW (D16).
A portion of oscillated VCO output signal from each VCO is
fed back to the PLL IC (IC15), through the buffer (Q32) and
LPF (L11, C210 and C231).
The applied VCO output signal is divided and phase-
MC1
compared with a 15.3 MHz reference frequency signal from
the TCXO (X3), which is also divided. The resulting signal
is output from the PLL IC (IC15), and DC-converted by the
J1
loop filter, and then applied to the VCO as the lock voltage.
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
15.3MHz
CR-794
X3
IC7
BAL
BUFF TCXO
REF
Q26
PLL
X3
IC
IC15
45.9MHz
IF IC
BPF
IC16
*:For [EUR] and [UK] versions.
**:For except [EUR] and [UK] versions.

4-4 VOLTAGE BLOCK DIAGRAM

IC20
PWON
+5V
VCC REG
IC6
CPU5
REG
VCC
ANT
4-3
Q23 Q29
RX VCO
RIPPLE VCO
R5V
FIL SW
D10
Q25
D9,D10
LV
ADJ
Q30 Q31
LOOP LV
BUFF BUFF
FIL
D11
D11,D12
LVA
LV
Q27
ADJ
TX VCO
Q32
BUFF
HPF**
×2
Q17
T5C
T5V
T5
To the TX circuits
REG
Q16
R5C
R5V
R5
To the RX circuits
REG
Q15
S5 S5V
To both RX and TX circuits
S5C
REG
+5V
To both RX and TX circuits
CPU5
To the logical circuits
F1
S5
1 2
D17
D16
TX/RX
To the TX AMPs
SW
LPF*
Q37
1st IF mixer