[lug] ethernet cable tester

[Carl.Wagner at Level3.com]

Hold the plug up, contacts facing you, cable going down towards the floor, pin
1 is on 
the left.

A cheap cable tester can be made by using 3 RJ45 jacks, 4 different value
resistors and 
a DMM or VOM.

Example
   on one jack:
      pins 1 and 2 place a 100 OHM resistor.
      pins 3 and 4 place a 220 OHM resistor.
      pins 5 and 6 place a 440 OHM resistor.
      pins 7 and 8 place a 1M OHM resistor.
   plug the cable into the jack.  At the other end put the second jack and
place a probe 
     on pin 1 and search for anything that will conduct. Check the resistance
and then 
     you will know which pair you have.  You can go back with a different
pin/resistor
     arrangement if you think you have a pair that is flipped (see below).

   If you want to check for flipped pairs, take the remaining jack and wire
it:
      pin 2 and 3 place 100 OHM resistor.
      pin 4 and 5 place 220 OHM resistor.
      pin 6 and 7 place 440 OHM resistor.
   And make a table from the result of the above 2 configurations.

Or spend the $100 to get the tester and be done with it.

Carl.




   

Deva Samartha wrote:
> 
> >At 11:36 AM 12/18/00 -0700, you wrote:
> >
> >I would bet that it has 2 jacks and you plug both ends of the cable in to
> >check
> >for miswires.  Otherwise you just about have to have at least a passive device
> >on the
> >other end.
> 
> It has a passive device with LED's to be hooked on the other end of the
> cable and it has two jacks on the main unit to test a cable without using
> the second unit.
> 
> As for using an ohm meter (to find the broken waar) in order to accomplish
> the same task as the tester does - yes possible, in theory, practically -
> not me.
> 
> First, getting the Cat 5 cable ( round, wired come out rather arbitrary )
> stripped and the 8 wires correctly fitted in the jack by color code and
> crimped proved at somewhat challenging - the stripes are hard to see,
> obviously, the cable manufacturer is saving on paint.
> 
> Second - to test the 8 wires, one would either need a needle thin probe tip
> to go on the jack contacts - possible in theory, practically - not me. A
> jack with a short cable and some kind of  breakout box would be thinkable,
> but then, how would one test a cable pulled through the attic two rooms
> further? One would need another wire  - connected to the ohm meter running
> to the plug in the second room from here, a person there to please test the
> first wire  - which one? - first from left or right - yea, plug facing up
> or down - cable coming from left....
> .. or a second cable running on the floor to the next room with a jack
> receptacle to do the broken waar finding alone.
> 
> Or make some kind of loop back plug looping individual pairs back to be
> able to test conductivity - 4 pairs, 8 wires??  Figuring this out -
> possible in theory, practically - not me.
> 
> With the cable tester - after getting the wires in the jack ( I've done it
> and I am proud of it!)
> plug the tester on one end, switch it on, got in the other room, plug in
> the secondary unit and watch the LED's lighting up in sequence - works, if
> not, check again the jacks with with a magnifying glass to find the problem.
> 
> I am not expecting to run into impedance problems or any other signal
> impairment issues  at this point where I would need something more
> sophisticated ( and $$++ ).
> 
> Of cause, the construction yellow may cause some illusions I am not willing
> to face just yet.
> 
> Samartha
> 
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