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Noise Interference on CAT5 Lines. Can you explain

I was using my toner to trace where my ethernet cables are patched to in this large building. The toner did not work. I assumed I should turn of my switches and maybe that would help. The problem I am having is whenever I put my toner to listen for the signal, i can literally hear the radio on my ethernet lines coming through my toner. This was amazingly bizarre to me. Do you know what this could be. I am only assuming this is one of the problems affecting my network. Please advise.
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cybercity216
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cybercity216
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2 Solutions
 
CallandorCommented:
The twisted pairs in cat5 are what keeps the cable free of interference.  As long as you don't untwist them, all you need to do is use a cat5 line tester on each end to transmit and receive and you will see if you have connectivity.  Cat5 is very good at rejecting interference, which is why you can even send video signals over cat5.  Using a tone generator works with phone wire, but the internal twists may mess up tracing.
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maduropaCommented:
UTP stands for unshielded Twisted Pair, so no shielding.

Furthermore, radio is transmitted on waves, and the unshielded cable will act as an antenna,
maybe your cable has the ideal length for a certain station. In order for good reception try to tune the cable by trimming a little bit.

I don't know the specs, but the radio-bands are on a different wavelength than Ethernet, so they can co-exist on the same line.
This effect is used to put ADSL-lines on normal copper-lines for telephone. To avoid interference, you use a splitter.

For not getting the signal, try to remake the connections, there might be a breach somewhere
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jhanceCommented:
As noted, CAT5 UTP should reject interference quite well in spite of having no shielding.  A twisted pair wire does not work well at all as an antenna because any signal induced in one wire in the pair gets a corresponding negative of that same signal induced in the other wire and the SUM of the two is ZERO (or darned close to it).  Of course this is why you should not unwind the pairs very much at terminations.

The fact that you hear radio signals on the wire tells me that you have a poor connection on the wire.  An oxidized connection or a break in the wire can produce a where AM or FM radio signals are coupled into the line.  Yes, this could definitely cause problems with your network as well.

If, on the other hand, you are running your UTP a very short distance from a radio broadcast antenna, then all bets are off.  That is an extreme situation and needs very special handling...
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cybercity216Author Commented:
Well, i have about 100 or so CAT5 cables going from the computers about 50sqft away, to the patch panel, to the switch which is about 5 feet from the patch panel, to a router which is 2 inches away. this is confusing.

regardless of where i put my toner, i and what CAT5 i try to listen on, i get the interference. in short, everyone of these cables is getting the RADIO signals.

the cables are not untwisted, we bought them, made our own ends, and only untwisted so we could add an end. the cables are quite long, do you think that is the main problem?
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CallandorCommented:
Cat5 is rated for close to 200 feet, so I don't think distance is your problem.  You must be close to a broadcaster, or something in the building is acting as an antenna and is connected to your network and is leaking it.
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cybercity216Author Commented:
what i mean by long, is the building is huge. there are cables are running about the entire building which is approximately 10000 sqft.
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jhanceCommented:
Is it possible that your "toner" is defective or just overly sensitive?  I've used on one of these but never picked up radio broadcasts.  

Is it possible that someone is using one of your CAT5 wires for something other than network?  It's quite possible to put audio on the wire.  Maybe your toner is picking that up...

Another possibility is the unused pairs.  Since these are often unconnected at one or both ends, they can act as antennas and pickup nearby radio signals.
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jhanceCommented:
Callandor,

You said: "...Cat5 is rated for close to 200 feet..."

If I'm not mistaken, I recall that the maximum length for a segment using CAT5 wire (used for 10BaseT networking) was 100m or about 320 ft.
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CallandorCommented:
Yes, 100m it is.  Some bits fell off into the bit bucket on that one.  I was thinking about another spec that had a 200-ft limitation, but it wasn't cat5.
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cybercity216Author Commented:
Thanks again you guys. I think that may be my issue. i did find a few cables that were unpatched, going from terminal jack, to patch panel and not switch. so i will investigate that, and loose wires.
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