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Problem with coax segment on network

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by mis

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We have a network (Cat5) in the building and one coax segment to connect the restaurant that lies beyond the reach of cat5. Lately the coax segment started giving problems. The connection would just drop and would connected again after I unplug and replug the hub in the main building. This hub is connected to a 3Com switch 4200 series. The hub itself is a 3Com TP16C. During the problem this hub would indicate that the coax segment has been partitioned by the hub. I cannot find the reason why this is happening. Do you have any suggestions?

Thanx

5 replies

by sgt_shultz

have you double-checked the terminator resistors that should be present on each end of the coax?
anything added/changed lately in the building? air conditioning motor or relay or other source of emf near the coax?

by mis

Both terminators are in place. I even tried different hubs but with the same results. The malfunction usually starts at the same time each day. One thing that did change in the building was that the ducts through which this cable was running was unearthed and some cables removed from this duct and the duct replaced. Could it be possible that the terminator lose their impedance??

by budthegrey

If the cable's been disturbed, it's more likely that one or both of the connectors needs to be re-done, or perhaps a t-connector replaced. Ethernet coax is, at best, skittish. A marginal connector will cause the symptoms you describe.

by pgm554

A couple of suggestions:

1.If you have a Digial volt meter , check the impedence of the resistors(should be 50 ohm).They do go bad.

2.If you have access to a TDR(time domain reflectometer),it can give you a real picture of whats going on (ie microbreak in the coax).If not bring in a cable guy with one.

3.If you are using thinax (rg58)it can be no longer than 185 meters and MUST be grounded at one end.If it isn't,it will still work ,but will be flakey at times.

4.Flakey or chattering NIC.

by wlbowers

Beg borrow or steal a TDR and do a sweep of the cable. (time domain reflectometer)

If you can't get one contact a contractor who can.

This instrument will provide you with a visual of your cable from one end to the other. You will be able to see each connector and terminator. It will also show you if the cable has been damaged.

Good Luck Lee

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