Sailor RM2042 Technical Manual page 72

5 CIRCUIT DESCRIPTION AND SCHEMATIC DIAGRAMS
SIGNAL SWITCHES AND CONTROL LOGIC
The receiver module contains two analog switches, which are included in the CMOS-IC U6.
The first switch is only used for loop back test purpose and is controlled by the microprocessor.
The second switch is used for switching between the build-in channel-70 receiver and the connected VHF
radiotelephone. This switch is controlled by the logical signal Q, which is generated by combinating the
output of the channel-70 carrier detect circuit and the two logic signals A and B.
The function of the signal switches and the corresponding control logic is described by the block diagram
below, which also include the logical circuits used to genereate the CH70 CARRIER DETECT, VHF
CARRIER DETECT and MODULATION DETECT signals.
RM2042 Receiver (Module 3)
U6
Build-in
Channel-70
Receiver
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The truth table for the switch controle signal Q is shown below.
NOTE! The signal CD is generated by means of the Channel-70 Carrier Detect circuit and indicate
whether a carrier on channel 70 is received (CD = '1' if a carrier is detected and CD = '0' if no carrier is
detected).
A B Q
0 0 1 CH70 used for reception of DSC.
0 1 0 VHF used for reception of DSC.
1 0 CD VHF used as default for reception of
DSC, but CH70 used instead if carrier
detected.
1 1 CD
PAGE 5-16
U7.3
de-emphasis
filter
U3.3
U6
de-emphasis
filter
Channel-70
carrier
detect
CD
U5.1
U5.2
U9.1
REMARKS
U7.4 U2
XD (Tx data)
Tx AF
FSK
filter
encoder RSI (Request to send)
RD (Rx data)
FSK
Rx AF
decoder CD1 (AF Signal detect)
filters
VHF
VHF-Carrier detect
carrier
detect
Modulation detect
U9.3
U9.2
Q
Channel-70 Carrier detect
U9.4
RM2042
External
Rx
Connected
Tx
VHF
Radiotelephone
B
A
Loop back test
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