Protect Signal (Fs-2575 And Fs-5075) - Furuno FS-1575 Service Manual

3. PROTECT signal (FS-2575 and FS-5075)

For details, refer to information on pages 7-12 to -14.
The PA-IF board (05P0864) for the FS-2575 and FS-5075 systems has a built-in TX
output power protection circuit. This circuit protects the transmission amplifiers by
producing a PROTECT signal on the basis of the PA IC and SWR-VR signals detected
from the DRV, COMB, and PA boards, and controlling the bias of 1st amplifier of the
DRV board to reduce output power to the threshold when an detected level exceeds the
threshold of any of the detection signals.
The PA-IF board (05P0864A) for the FS-1575 system contains no TX output power
protection circuit. However, a circuit providing the protection function is incorporated
in the PA board.
DRV (05P0866A)
TX (05P0865)
Q2
Q1
U6
Q3
Q1
BIAS
Power
Cont R77
Q1
BIAS ADJ.
CR8
U1
CR7
U1
PA-IF (05P0864)
VS
U6: VS
DET
CONFIDENTIAL (internal use only)
This confidential document is used only by FURUNO authorized persons.
It is strictly prohibited to reproduce the document in whole or in part without prior written permission of FURUNO.
Q4
DIV
Q5
SWR DET
R78 R79
Q2, 3 Q4, 5
BIAS ADJ. BIAS ADJ.
TEMP
DA
PROTECT
U2
ALC
U5
VS2
U5
VS
MOT (05P0860)
T-CPU (05P0859)
Fig. 7.2.17 PROTECT Signal Circuit Diagram
7-36
PA (05P0867A)
PA-1
COMB
(05P0869)
to PA-IF
ADC
PA-2
PA
Q2
CR2, 3
Q3
SWR DET
PA
TEMP
from PA-1
PA1 IC
PA2 IC
VR PA1
VR PA2
UN_BAL
ADC (U7, 8, 8)
PAIF ADC DATA
7.2 Transmission Circuit
TX FIL (05P0870A)
T1, T2
L1 L18
PA B.P.F
x 8 Band
IN VR/VF OUT VR/VF
B.P.F
VR VF VR
DET
U1
R43
ALC VR
T/R ANT
VF