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Problems making my own patch cables.... 2

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udpstorm

IS-IT--Management
Aug 24, 2003
10
US
I am experiencing some problems creating my own cables. I crimp both ends and connect PC to LinkSys cable router and I get a link light but no action. No DHCP nor will a static address work. I have tried various lengths of cable, different crimpers and crimp brands and no luck. I used a meter to confirm continuity through the cable. I can't seem to find out what the problem is.

I need to run lengths of 120 to 300 feet. My understanding is that I should be able to run up to 331 feet?

 
I went back and checked out the website he was using as a reference. It shows a picture of a plug wired 568B, but then states the following:

>> In general, the patch cords that you use with your
>> Ethernet connections are "straight-through", which means
>> that pin 1 of the plug on one end is connected to pin 1
>> of the plug on the other end. In this particular case
>> it is not then important to wire them as shown. Pin 1
>> is Pin 1 etc etc. However for the sake of uniformity it
>> may be best to wire your cables with the same colour
>> sequence throughout.

It is not then important to wire them as shown??? It MAY be best to wire with the same sequence throughout???

The site should say it is vitally important to wire them as shown (or as 568A) and you must wire with the same sequence throught. It IS NOT enough to just connect pin 1 to pin 1, pin 2 to pin 2, etc. Pins 1&2, 3&6, 4&5, and 7&8 MUST be maintained as pairs. Its a shame people put out incorrect information like that.
 
Your pinout explains why it doesn't work, since you are splitting the pairs. 10BaseT and 100BaseT transmit and receive on pin 1 & 2, and 3 & 6.
If I read your explanation right, you are using the orange pair on pins 1 & 2, and the blue/white on pin 3 and white/green on pin 6.
Since that means the pair on pins 3 & 6 is NOT twisted together, they cannot cancel crosstalk. So the longer you go, the worse it gets till the receiver cannot tell what is on the line. Kind of like trying to listen to a conversation in a crowded echo chamber.
This is why I never cared for the terminology "straight through” not exactly accurate. You can't as some web sites suggest and others have claimed, just wire pin to pin.


Richard S. Anderson, RCDD
 
TouchToneTommy & DToolsDesigner you have hit the head on the nail. although there are more than crosstalk issues at stake when you split up the pairs. you also have resistance, impediance near-end-cross-talk, capacitance, and loss. each of the pairs has a tight twist to them and to keep the wires from laying really close to each other in the bundle the different bundles are all twisted at a different rate per inch then the bundle is sheathed in a loose sheath to let the wires flex around.

Useually when you are making up longer runs of cables it is the best idea to put cat5 jacks on each end, (even radio shack has single jack boxes now) and then run short cords to the equipment. the advantage of jacks is that they provide the two colorcodes to follow so you don't get screwed up (I prefer 568B) If you have to make up cables with plugs on them for some reason I start with pulling teh sheath back about an inch, then unwraping the wire pairs and straightening them (if you pull a wire between your thumb and a round object like a pen the kinks from the twisting will disappear) put them in order and cut off all but about 1 inch of wire. still holding them in order slide the plug on and slide the sheath up(if you let go too early start over since you will have lost the order in the plug) then crimp the cable with enough of the sheath in the plug to provide strain relief.

biggest thing I find undesireable with putting plugs on the end of cables is that they go bad for reasons people have stated earlier and you keep cutting off a few inches to re-terminate and eventually the cable is too short to work with.

JerryReeve
Communications Systems Int'l
com-sys.com
 
Jerry nice summary. I actually went over to Radio Shack and I am using the 568B scheme.
 
although there are more than crosstalk issues at stake when you split up the pairs. you also have resistance, impediance near-end-cross-talk, capacitance, and loss.

Hmm, if I wired a cable with the pairs split, how would that change the resistance? How would that change the capacitance? Why would there be a difference in loss? I'll grant you the NEXT, FEXT, etc. will definately be an issue, and possibly delay skew and noise, but I don't see your logic on the other measurements.

Can ya explain it for me?


It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com
 
Yes, it would cause more than just a NEXT issue, but frankly I didn't see the point of going into such things in this forum. Usually I get paid quite well for such discussions.
The other thing it would certainly impair is Impedance. Thus creating an Impedance mismatch, which in turn would cause Return Loss or reflected signal. This would be due to the fact that each conductor of the "pair" on pins 3 & 6 may be a slightly different length.

All that said, it doesn't change a thing as to what the original problem was. The only thing it would probably accomplish is to confuse those that are trying figure out why the cables didn't work.
Transmission theory is not the easiest subject to comprehend, especially in 3 or 4 paragraphs of type.


Richard S. Anderson, RCDD
 
I'll have to bail out on the theory also, I remember going over it way back when. the main reason I made that statement is that is some of the scanner test failures that can be seen when the wrong wiring scheme is used. it can fool you since the scanner shows that the pins are straight thru but other tests fail. I have to open up the connections to see what actually causes test failure. Just a loop in the cable that was pulled tight can get you failures.

JerryReeve
Communications Systems Int'l
com-sys.com
 
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