Comtech EF Data SDM-300A - Manual (Page 281)

SDM-300A Satellite Modem Revision 6
Open Network Operations MN/SDM300A.IOM
10–25
10.5 G.703
Note: If required, refer to Chapter 3 for installation of the interface PCB.
G.703 data is either in AMI, B8ZS (8 zero) suppression, or HDB3 (3 zero) suppression
formats. There is not a coexisting clock that is on a separate line for G.703 data. The
clock is derived from the data stream within the modem and in the user equipment.
Loop timing, if desired, must occur in the customer equipment for the link to operate in
Master/Slave. The modem cannot do loop timing in G.703 operation because the modem
does not emit an ST signal for the Transmit Clock Source.
The modem can be placed in loop timing under EIA-422 or V.35 operation. Therefore, a
master/slave relationship easily occurs. This causes the receive clock to be placed on the ST
line to the terrestrial equipment. The customer equipment can then clock the transmit data to
the modem using the ST line that has been derived from the RX recovered clock.
10.5.1 G.703 Specifications
Table 10-7. G.703 Specifications
Parameter Specification
Primary Data Circuits Supported T1 SD, RD
E1 SD, RD
Interface Type Transformer coupled symmetrical pair
Data Rates T1 1544 kbps ± 100 bps
E1 2048 kbps ± 130 bps
Pulse Width T1 324 ± 50 Ns
E1 244 ± 25 Ns
SD Amplitude T1 3V +0.3/-1.5V-pk into 100 Ω
E1 3V +0.3/-1.5V-pk into 120 Ω
RD Amplitude T1 3V +0.3/-1.5V-pk into 100 Ω
E1 3V +0.3/-1.5V-pk into 120 Ω
Pulse Mask T1 G.703.2
E1 G.703. 6
Jitter Attenuation T1 G.824
E1 G.823
Line Code AMI, B8ZS, B6ZS, HDB3