Wouldn't there be 8 to the 8th-power possible combinations for 8 pin
connections? (Someone may wish to check my math. There are 64
combinations if you just keep the wires in the same order just shifting
them over!) But only one of those would place the "twisted pairs" into the
correct EMC signal configuration. Otherwise you might be placing different
data signals together onto the same "twist" and splitting the signal pairs
up onto different "twists". This would obviously work to some degree and
for some length, but the EMC benefit of the twisted pair would then be
lost. It only works correctly for EMC in one configuration out of
16,777,216 possible combinations. (if my math is correct).
-----Original Message-----
From: John Pelham
Ford wrote:
>When you hook up the cables to keep the colors all the same on each
>pin at each end, you will have conductivity between the correct pins,
>and the network will work, but you completely lose any shielding benefits
>of the twisted pairs.
I don't follow. I assume you mean by "colors all the same on each pin at
each end," you mean that if at one end the green wire is on pin 6, at the
other end the green wire is also on pin 6, for example. It seems like
you're saying that this is the wrong way to do it. I've made zillions of
Ethernet cables and have always done it this way. I just checked my wiring
reference and it says to do it this way. (I'm not talking about the
special
category of crossover cables, just regular Ethernet wiring.) I don't see
how doing it this way is wrong electrically. In fact it seems like doing
it
any other way would be wrong and would likely not work at all.
Am I misunderstanding? If not, how would you have us wire Ethernet cables?
73,
John W1JA
----- Original Message -----
From: "Ford Peterson"
...SNIP...
> I was surprised to find that grounding the EMT to the #4 Cu wire that
> comes in from outside INcreases the level of these unwanted signals by 2
> S-units. Any ideas why, and what I could do to get rid of this RFI
> (until I get the tower up, at which time the feed point will be much
> farther away from any of the computer equipment)?
>
> Alan NV8A
Alan,
One of my pet peeves is when computer technicians wire cat5 cables
incorrectly. There is a right way and a wrong way to do it. The right way
is the most difficult. Guess which way most people do it?
The 8 conductors in that cable are actually 4 pairs of twisted cables.
Each
pair is a "hot" and a ground return. When you hook up the cables to keep
the colors all the same on each pin at each end, you will have conductivity
between the correct pins, and the network will work, but you completely
lose
any shielding benefits of the twisted pairs. You should not be hearing
anything from that cable.
I do not have the specification for those cable ends handy. But as I
recall, the ground returns are the 4 pins on one end of the connector.
Before rewiring your house with EMT, I would make sure the connectors are
installed correctly.
I have one run here that an 'installation expert' installed for me. I
queried him explicitly on the correct wiring pattern. A lively discussion
ensued. Realizing that I was arguing with an idiot with 7th grade shop
class electrical wiring experience, and that I was paying him $2 a minute
to
argue with me, I let him wire it his way. Not surprisingly, that
particular
75' run of Cat5 never runs over 10mb in a 10/100 hub. The hub shifts into
low gear to deal with the noise.
I'm sure short runs work just fine wired however you want. Wired the
'easy'
way, you get 2 pairs carrying all the data and two pairs acting as the
ground return. I'm sure there is some shielding afforded by lashing them
into the same run of wire, but they are not acting correctly. It takes 4
thumbs to wire them correctly. Find the spec and wire them right.
Ford-N0FP
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