Sailor RM2042, Technical Manual, Page: 72 / 106

5 CIRCUIT DESCRIPTION AND SCHEMATIC DIAGRAMS RM2042
PAGE 5-16 9341
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.
Build-in
Channel-70
Receiver
U6
decoder
FSK
encoder
FSK
U2
carrier
detect
VHF
Connected
External
Radiotelephone
Rx
Tx
XD (Tx data)
RSI (Request to send)
RD (Rx data)
CD1 (AF Signal detect)
U9.3
U9.2
Modulation detect
U5.2
U5.1
VHF-Carrier detect
Channel-70 Carrier detect
de-emphasis
filter
filters
Rx AF
Tx AF
filter
VHF
U7.4
U7.3
U9.1 U9.4
B
A
Loop back test
U3.3
de-emphasis
filter
Channel-70
detect
carrier
U6
RM2042 Receiver (Module 3)
CD
Q
27542
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 REMARKS
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