Furuno FS-1503, Service Manual

Page: 26 / 136

2-19
Note) PA amplifier is high-frequency-grounded to -13.6 V line through capacitors C49
to C52.
ATT
-1.5 dB
TX/RX
EXC OUT
PA OUT
13.6 V +
AVR
PA BIAS
DRIV BIAS
PA ON
R39
PA BIAS
RT2
PA ON
TEMP
Q4
Q5
Q6
Q7
U3
5V
U4
U6
Q8/U2
Q9
J1
7
6
T4
T1
T2
2SC3240 2SC3133
R14-16
FL3
R69
Power on/off
Circuit
Q1, 2, 3, 11, K1
RX IN
K3 (BK)
FIL
13.6 V –
PA IN
C49 to 52
PA Temp Detector
Figure 2-11 Block Diagram of PA
The PA output is supplied to L.P.F.'s B1 to B6 to reject spurious signal components. The-
se filters are commonly used for transmitting and receiving. Their losses are less than 1
dB.
Relays are used to switch each filter ON/OFF. U8 drives the relays with the parallel data
which is converted by U7 from the serial data signal sent from CPU in accordance with
the set frequency.
L.P.F
K10 K4
L.P.F
K11 K5
L.P.F
K12 K6
L.P.F
K13 K7
L.P.F
K14 K8
L.P.F
K15 K9
B1: 0.1 to 2.4 MHz
B2: 2.4 to 3.6 MHz
B3: 3.6 to 6.0 MHz
B4: 6.0 to 10.0 MHz
B5: 10.0 to 18.0 MHz
B6: 18.0 to 30.0 MHz
Vf Vr
T5
CR6 CR7
ALC
RF
U4 2/2
U5 1/2 U5 2/2
RX OUT
PA IN
K3 (BK)
ANT
CLK
DATA
ST FIL
U7
K3 (BK)
K4 to 15
(B1 - B6) U8
Figure 2-12 Block Diagram of FIL (TX)
T5 detects the traveling wave voltage (Vf) and reflecting wave voltage (Vr) on the output
signal of the L.P.F. CPU receives the traveling wave voltage component and processes it
for the RF meter indication.
U5 1/2 amplifies the detected traveling wave voltage component and U4 2/2 amplifies the
reflecting component. Both voltage components are amplified by U5 2/2 and derives
ALC control signal. The ALC signal inputs to U8 2/2 on TX/RX board and automatically
controls the transmitting power on the basis of the set power data. The signal is also used
to protect the PA when the power output is opened or short-circuited.