Testing a long run of cable

[nigelmercier]

I've got one of these, works fine
http://www.amazon.co.uk/exec/obidos/ASIN/B004BVIIAS/dolcetto-21

Ideal for testing any network cables on a boat.

Made my day seeing that someone somewhere still remembers TOKEN RING

Didn't he write The Hobbit?

 

[William_H]

Just as a matter of interest and alluded to by a previous poster. As said the cable is probably bad at either end. However..... Long cables can be tested by feeding into the end of the pair a short square wave pulse. You connect an osciloscope in parallel with the pulse generator. If the cable is correctly terminated at the far end then you get no reflected pulse. If the cable is short circuited you get a pulse reflecting back from the fault. Likewise if the cable is open circuit you get an inverted pulse reflected back as seen on the osciloscope display. You can calculate from the speed of light the distance that the fault is away from the tester by the time delay and divide by 2. (return path)
This is the essence of some cable testers. Very useful for long telephone lines etc. av bit like a simple radar. Possibly useful to OP if he has a really long cable in his really long boat. Most of us with short boats just replace the cable. good luck olewill

 

[peter2407]

That'll be me then..

Rare but not unknown - if you have rodents about - The little b******s ate right through a six-core of mine!

I do suspect squirrel activity - the dinghy sailing sort of course, or maybe rats (but then I would need to move the post as they tend to be MoBo types ... Or even jet skiing rabbits, which would be real conundrum re posting ....).

 

[davids0865]

I would suggest the easiest thing is to look at both ends and put a new socket on whichever looks more suspect.
Try it again and see if that cures it.
If you want to check out individual cores, the easiest way is to cut a patch cable in half plug half into each end, on one half short each pair, on the other measure the pairs with a multimeter.
Also make sure the system s not expecting a crossover connection.

With apologies for fred drift, under what circumstances do you need a crossover connection?

 

[VicMallows]

With apologies for fred drift, under what circumstances do you need a crossover connection?

One common application is connecting two computers directly together via the LAN connections

 

[JumbleDuck]

With apologies for fred drift, under what circumstances do you need a crossover connection?

Roughly speaking ... most devices have a "transmit" (Tx) wire on which they send out information and a "receive" (Rx) wire to which they listen. When you connect computers, plotters and so on together with a router, the router listens to each device's Tx line to hear what it's saying and then send it down the appropriate device's Rx line. The convention for doing this is that the Tx and Rx connections on the router are reversed, so that it listens to what other things are sending and transmits where other things will listen.

If you are simply connecting two devices together you need to make sure that Tx on each connects to Rx on the other and thats when you use a crossover cable, which does that reversal.

I can't offhand think of any reason why routers, switches and so on couldn't simply be wired to expect crossover cables. It would, however, make it a bit of a pain putting plugs on, as you'd always need to know how the other end was wired. So it's probably easier to have the vast majority of cables wired straight and just swap the odd computer-computer ones.

Boatie boatie boatie boatie boatie anchor boatie boatie.

 

[lw395]

Crossover connections were a real wind up to me at one time.
But not as bad as finding you have 'power over ethernet' when your device is not expecting it....

These days most hubs, switches etc automatically sort out the crossing over for you.