10Base2 Resistance Question

No. That's not the issue. You do have TWO terminators, one at each end, right?

Sanity check. According to my calculations, the center conductor of RG58U cable has a resistance of about 12 ohms/1000 ft. The coax braid adds insignificently to this. Anyhow this means that the measured resistance of 500 ft of cable + terminator will be about 6 ohms greater than the terminator by itself.

This of course is not measured in the presence of the near-end terminator.

carl

David,

The measurement was take with only one end terminated. When I connect the cable to the actual switches at either end of the line I install both terminatros. Now, since this was setup before I ever came here there is one other peculiarity: none of the terminators are grounded, could this cause an issue?

James Thomps> > >"james.thomps> >

I've never seen gounding, or lack of it, causing a problem with thinwire, but one end should be grounded.

What is your actual problem?

Nope. No grounds needed. (Nor desired)

Something else must be wrong....

I think I have isolated it to equipment but here is how the setup is and what is not happening:

We have a 500 foot segment from Building A to B, another 350 foot segment from B to C and finally a 550 foot segment from C to D. Each cable is segmented using 3Com OfficeConnect hubs that are then linked together via crossover cables to connect the various segments. The network services that are provided in Building A are not accessible from anywhere else down the line. We had a really wicked lightning storm here a week ago which immediately preceded the problems we're having.

Currently the OfficeConnect hubs are failing to partition themselves when the 10Base2 is disconnected which is leading me to believe there may be a fault at that level, however, if the fault was caused by the lightening I worry that the cables themselves may have been adversely affected. The 10BaseT portion of these hubs still functions as expected though.

James Thomps> > >David,

Classic lightning hit symptoms. Cheap solution, put in cheap hubs for the interbuilding links. Buy spares, as they will function as fuses every time you get a lightning hit someplace within a mile or two with sufficient energy. Unlikely the cable itself is damaged. Permanant solution. Yank the old cable and install some optical fiber between buildings. Pull in lots more strands of fiber than you think you need. Once you have it, you will find all sorts of uses for it.

--Dale

Enough Said.

Never EVER string Ethernet between buildings; UTP or FAR worse, coax. You are asking for sure grief.

If you are lucky, you just cook the hubs at the end. If you are NOT lucky (and recall Murphy has a far longer list than Santa, and works

Short-term solution. Buy some 10 MB FO converters, and a 3' length of fiber, for each line:

-----------------------FO===FO---etc A BBBBBBBBBBBBBBBBBB

and break the loop with the fiber segment. Better, do it at both ends. BEST, replace the coax with glass.

It does not take direct hits to cause $10-100K worth of damage, no including loss-of-business..

I agree with people re earthing the segment(s).

I am SURE a bit of kit has been nuked by lightning induced surge.

First choice - Fibre

Second choice - UTP plus PROPER protectors just inside both buildings plus cheap switch a metre from the protector in the main building.

Third choice - UTP plus cheap switch at entry point of each building, plus sign off by management that they happy to take risk.

Good luck! Philip Partridge

I'm pushing for fiber, but I inherited this system and it was only installed a year and change before I came so there is some desire to make it work. The problem is that the school I work for is out in the middle of nowhere (25 minutes to a non-Super Walmart, 1 hour to a Super Walmart, and 2 hours to the nearest city with any fiber experience) so we have to maintain a lot of stuff ourselves and keep the costs down since we are wholly supported by donations.

I've got a proposal in the works to move to fiber optic but it's going to cost more than they are accustomed to spending on such things, but at least they're willing to entertain the idea.

James Thomps> "james.thomps>

And then ground them back to the power service entrance at each building. NOT to a power ground connection near by. You can read about equipment grounding a bit to understand why.

I had a similar situation. After the 3rd $2000 plus loss of phone and computer gear (and I think we were lucky) we spend the money to change some things.

BTW, doesn't London doesn't have a Wal-Mart? Or is that where the non-super one is? :)

Manchester has the non-Super, about 25 minutes away and London has the Super, about an hour away, the driving distance is a little less the way I drive but it's still a good distance regardless...

James Thomps> james.thomps> > I'm pushing for fiber, but I inherited this system and it was only