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You are here: MacNN Forums > Enthusiast Zone > Networking > Shielded Ethernet cable questions

Shielded Ethernet cable questions
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Join Date: Jun 2009
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Jun 8, 2009, 07:29 PM
Hi everyone,

I would like to replace our standard Ethernet cable with something better. I will try to be brief in describing the situation.

We have:

1 cable modem
2 computers
1 four port wired router

It all functions fine; except, the blue Ethernet cable carries a high electric field, as well as emits RF noise (I can even pick it up with an AM radio at several or more inches).

I want a wired solution which will allow us to share our internet connection between the computers using the modem and router we have, but without the cable carrying an electric field (which I can only assume is being carried along from the router/modem, which of course are plugged into AC power)...

...and don't want the Ethernet cable to emit any RF. I'm more concerned with RF that's coming *out* of the Ethernet cable than what can pass *in* to it.

As far as the RF goes, I'm going to assume that it's being inducted (is that the right word?) from the information being processed in the modem and router, and is itself the data from the internet simply functioning. (The router, and especially modem emit a lot of RF, very audible with an AM radio, and also use what I guess are switching power supplies, adding to the noise).

So, I'd considered using multimode fiber optics...until I found out that I'd need a media converter at each end of the fiber optic cable! One at the router, one at my computer!

Simplified, my goal is to be as low in all electromagnetic radiation from all components as possible. Since this is what I'd like to achieve, using media converters for fiber optic cable wouldn't have a point for me, because they, themselves, are powered by wall-wart type AC-DC transformers, which generate strong magnetic fields, and a lot of RF noise.

What I'm trying to figure out is, will "shielded" Ethernet cable prevent the outward radiation of all RF noise generated by the data traveling along the cable?

I see MHz ratings given to a lot of shielded Ethernet cable; what does that rating mean? It's always a single number.

Assuming that shielded cable will prevent the outward radiation of all RF, can I further prevent the transfer of RF onto the shielded Ethernet cable from the modem or router by using shielded connectors such as this?:

RJ45 8P8C Shielded Connectors, 100-pack - RJ45SC, $40.95

Is this size, RJ45, standard? As in, the same plug that normal, commercial Ethernet cable uses to connect to computers, routers, modems?

Would ferrite clamps help, too?

Now, if all the RF shielding I want can be accomplished by using shielded Ethernet cable, the next question is this:

How can I prevent the transfer of the electric field from the AC powered modem and router from carrying all the way along the Ethernet cable?

(I know that's what it's from, rather than the Ethernet cable picking up electric fields from other wiring - I checked when the router was unplugged and there was no e-field on the Ethernet cable; plugged the router back in and the e-field on the Ethernet cable jumped way up).

A tech on the phone told me that it shouldn't induct the electric field, but the connection was wonky, and he or I may have misunderstood eachother; if a cable's shielding relies on conductive material, that would mean that an electric field would be, well, conducted!

Is there a way around this? Can a conducted electric field be contained at its source, so it doesn't follow a cable?

Please bear in mind that I'm not more technically knowledgeable than it seems by what I've posted. If anyone has suggestions how to proceed, can clarify if "shielded" cable actually entails that RF won't come out of the cable, how to further prevent RF from the router and modem from getting on the cable, which cable type to actually look for, and how to deal with the electric field, it would be hugely appreciated.

Thank you!
Join Date: Apr 2001
Location: San Antonio TX USA
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Jun 8, 2009, 10:05 PM
I think it's less likely that a Ethernet cable is what's producing the field you are picking up with a radio than some bad power cord somewhere. The voltage levels on Ethernet are way too low to do that, and the frequencies are all wrong for being picked up by an AM radio. It's more likely that the power unit for your router is faulty, or there's a fault inside the router. In technical terms, it sounds like you're experiencing a "floating ground leak," where the neutral side of your two-prong power plug is not at ground/earth potential, which makes the ground reference level inside the device fluctuate according to whatever potential that neutral lead is at. This is caused by bad wiring, a bad outlet, or both, and it would be a VERY good idea to have your outlets checked by a professional electrician ASAP.

However, using shielded cables isn't "bad." Just expensive. Technically, Ethernet cables are "UTP" or "Unshielded Twisted Pair," though a LOT of cable (maybe all of it today) is actually shielded to some extent. Shielded RJ45 plugs sound great, but they only do anything worthwhile if they plug into JACKS that are shielded. Not much consumer hardware uses such jacks. I would definitely NOT spend the rather hefty money to buy such connectors, then spend the frustrating effort in installing them on your cables.

Get your outlets checked NOW, and get 'em fixed if there are any problems at all. I'm betting there's something amiss with where one network device or other is plugged in.

Glenn -----OTR/L, MOT, Tx
Join Date: Oct 2001
Location: San Jose, CA
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Jun 9, 2009, 02:05 AM
I guess my question would be why are you worrying about this? I don't think the levels of EM radiation are going to make you sterile or anything, and, as mentioned, ethernet is low power. What are you trying to accomplish in going through all this that's going to probably end up costing way more than the standard cat 5 cable you can get anywhere?

(I'm guessing a wireless network is completely out of the question.)

Celebrating 10 years and 4000 posts on MacNN!
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Jun 12, 2009, 01:26 PM
I'd also say go w/ the wireless network option.

You'll spend way too much time, $$ and effort trying to find out what exactly is causing all of this interference (what you're hearing come through on your AM radio).

You could try to solve the problem by buying a wireless networking router -- just make sure to save all of the packaging so that you can return it if that doesn't solve the problem.
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