Solution:

The following is for your information: 1. Network A: The network A is successful for 1km, but not for 1.5km. We just have 3 clusters of cable ( AWG #24, total length of one cluster is 500m ), it is inconvenient to test 1.2km for you, so we recommend you'd better shorten the length of trunk less than 1km or test 1.2km by yourself. 2. Network B: The network B is successful for 500m, not for 1000m. We also can't help you to test 800m because of cable. 3. Application of ADAM-4515: Actually, ADAM-4515 is properly used in network A instead of network B, if you want to develop star topology, ADAM-4515 is very suitable in this case. But if you want to use several ADAM-4515s to expend your network, you'd better pay your attention to delay problem.