What are the selection criteria for the line build-out (LBO) bits in E1 applications?
A4. The criteria depend not only on the intended application for the SCT, but also to what type of system the design is interfacing. The line interface circuit can be designed many ways and the following applications explain the difference in the three major operations obtained by switching the LBO. 75Ω/120Ω Normal This is used for E1 short haul, when the system will be used in a confined environment where the return loss is insignificant and there will be no exposure to lighting surges or power-line cross conditions. 75Ω/120Ω with Protection Resistors or 75Ω/120Ω with High Return Loss These two operations are used for E1 long haul, when the system will interact with the outside environment. Here, the return loss is also considered to be insignificant. In order protect the system from lighting surges and power-line cross conditions, power resistors are placed in between the RJ48 connector and the network side of the transformer.
