Product manual

Product Manual - DM991 Series V Family - 204.4092.08 25
5. G.703 - G.704 INTERFACE
The interface allows usage of coaxial cable (75ohms) or for twisted pairs (120ohms). The cables are
attached through transformers, so there is no polarity for the twisted pair.
5.1. DM991S/SE
There are straps which allow connecting the external net of the coaxial cable to the ground cable. This
works either for the input channel (RX-IN) as for the output channel (TX-OUT).
The output wire that goes through pin 18B of the EDGE 2x30 connector is connected to the central pin of
the E10 strap, and is the TX-OUT cable, that can be connected to the ground cable through this strap. In
this case, it must be identified for each cabinet model which was the TX-OUT screw to be grounded by the
strap, so it can be connected to the coaxial cable net. On the sub-racks, usually, the inferior TX-OUT
screw is grounded.
The input wire that goes through pin 21B of the EDGE 2x30 connector is connected to the central pin
through strap E11, and is the RX-IN cable, that can be connected to the ground wire through this strap.
The same identification procedure of which screw has been grounded must take effect in this case. In the
sub-rack, usually, the inferior TX-OUT screw is grounded.
Modem signal G.703 is available on Dial Backup terminals in the terminal strip.
Function Signal
screw connector
block
Signal source
Received data OUT core BkpC DM991
Received data OUT shield BkpD DM991
Transmitted data IN core BkpA E1 Network
Transmitted data IN shield BkpB E1 Network
Table 12. DM991S/SE - Pinout in the G.703 Screw connector block.
Function Signal DB25 Signal source
Received data OUT core 4 DM991
Received data OUT shield 17 DM991
Transmitted data IN core 2 E1 Network
Transmitted data IN shield 15 E1 Network
Table 13. DM991S/SE - G.703 Telebrás (DB25) Standard Pinout
When using twisted pair (120ohms), make sure the straps are not in the ground position.
When installing the DM991S/SE
, remove the protection varistors from the cabinet or sub rack. These
varistors deform the G.703 signal pulses, which can cause wro
ng bits, working intermittently, or even
completely stopping the circuit activation.
In case the cabinet or shelf was made by DATACOM or has
gas-filled valve arrester instead of varistors, no changes are required.