5902 Bell 202 Modem Hardware Manual
October 19, 2007
25
RF Carrier
Detect (RCD)
Received
Signal
Carrier Detect
(DCD)
Received
Data
data
(1)
(2)
(6)
Sequence of Operation
1.
Sender keys radio and begins transmitting carrier.
2.
Carrier is received after radio key-up and propagation delays.
3.
Carrier detect delay starts timing at carrier reception.
4.
Sender starts transmitting data after its RTS/CTS delay.
5.
Carrier Detect (CD) must be true before data reception.
6.
CD goes false after expiration of carrier loss delay.
7.
False character might be received here due to sudden carrier turnoff. Modem
is ready for next reception or transmission.
marks
(3)
(5)
(4)
(7)
Figure 14: Receive Timing without Soft Carrier Turn-off
RF Carrier
Detect (RCD)
Received
Signal
Carrier Detect
(DCD)
Received
Data
data
(1)
(2)
(3)
Sequence of Operation
1.
Sender keys radio and begins transmitting carrier.
2.
Carrier is received after radio key-up and propagation delays.
3.
Carrier detect delay starts timing at carrier reception.
4.
Sender starts transmitting data after its RTS/CTS delay.
5.
Carrier Detect (CD) must be true before data reception.
6.
CD goes false 4-10 ms after SCT tone starts. Receiver is disabled. No false
data is received since receiver is disabled before carrier turnoff.
7.
Ready for next reception or transmission upon loss of received carrier.
(4)
(5)
(6)
(7)
marks
SCT
tone
(8)
Figure 15: Receive Timing with Soft Carrier Turn-off
