Re: [RFI] Ethernet RFI

["John Pelham" <john@radiophile.com>]

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" <ford@cmgate.com>
To: "Alan NV8A (ex. AB2OS)" <nv8a@att.net>
Cc: <rfi@contesting.com>
Sent: Saturday, January 22, 2005 8:41 PM
Subject: Re: [RFI] Ethernet RFI


...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
ford@cmgate.com


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