Comtech EF Data SDM-650B - Manual (Page 63)

SDM-650B Satellite Modem Configuration
Rev. 5 3–21
DS-1 LINE
TO BUFFER
OPTIONS
TX CLOCK
DS-1
DEJITTER
RECEIVER/DRIVER
T
E
R
R
E
S
T
R
I
A
L
SD
RD
LOOPBACK CONTROL
M
O
D
E
M
TX DATA
RX CLOCK
RX DATA
MC EXTERNAL BUFFER CLOCK
TO BUFFER
COMMON EQUIPMENT
OPTIONS
LOGIC
CONTROL
FAULT
RELAYS
MODULATOR
DEMODULATOR
DATA BUS TO M & C
TTL MODULATOR FAULT
TTL DEMODULATOR FAULT
Figure 3-7. DS-1 Interface Block Diagram
The data to be transmitted by the modem is input on the SD lines. Jitter on the SD is
removed by a FIFO and clock recovery phase-locked loop. Data received and
demodulated by the modem is output on the RD lines.
The RD is driven from a pulse-shaper circuit which pre-equalizes the RD output to drive
up to 655 feet of ABAM cable. Refer to Table 3-3.
The DS-1 interface provides bi-directional loopback of the data at the DCE interface.
In loopback from the DTE side, SD is connected to RD.
In loopback from the modem side, the received demodulated data is routed back to the
modulator input for re-transmission.