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Author Topic: OK to Run CAT5 near the Antenna FEED Lines?  (Read 278 times)
KI4WZO
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Posts: 17




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« on: October 27, 2007, 09:02:11 AM »

I need to pull Cat 5 wires into my shack. I have a 2 Meter Feed line 58 coax (which uses 25 to 50 watts), and two coax HF feed lines (which use 100 and 200 watts).  The HF Feeds are "bury flex low loss" 50 ohm coax.  All Feed Lines are run behind finished walls in antenna wire chases before they reach the attic. Running the feeds  between finished walls wasn't easy, but I did leave pull wires in the wire chases, so it would be quick to run any additional cable inside the Ham shack feed wire chases.  Just pull that CAT5 wire and go!  The CAT5 cables would be parallel to and very near the feed lines for only 6 feet, a few inches apart-or less.

Concerns:  Am I going to have any  problems with crosstalk and such, since the run isn't long?  Will error correction fix these problems? Will I be corrupting data transfers in the CAT5 wires like this if I transmit in the middle of a big file transfer?    

Please Advise---Thankyou.  Best Regards.
Greg

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W5EUT
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Posts: 19




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« Reply #1 on: October 27, 2007, 09:37:46 AM »

You should be OK, if:

1.  Low SWR on coax lines and ground the shield at one end.
2.  Properly use the CAT 5E cable, it is 5 twisted pairs.  Use a pair for each circuit.  The twisted pairs tend to cancel out interference.

73 Jim
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N3BIF
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Posts: 1190




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« Reply #2 on: October 27, 2007, 09:40:11 AM »

 If coax is all you have in there it should be fine,  this is a big benefit of shielded cable (coax)
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AA4PB
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Posts: 12834




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« Reply #3 on: October 27, 2007, 09:53:25 AM »

I haven't had any problem. It is important that you don't have a lot of RF flowing on the outside of the coax shield. Contrary to popular belief, this is not caused by high SWR. It is caused by such things as running the coax parallel to a dipole or feeding an end-fed wire or vertical without an efficient counterpoise. If you aren't experiencing any "RF in the shack problems" now then you likely won't have any problems with the CAT5.

Definitely use the CAT5 pairs properly and maintain the tight twist. Normally only two of the four pairs are used, one for Rx and one for Tx.


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WB2WIK
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Posts: 20595




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« Reply #4 on: October 27, 2007, 04:35:51 PM »

If you haven't pulled the network cables yet, why not use CAT5STP or CAT6STP cable, which is 100% shielded?  It costs a couple cents more per foot, and it's better cable.  CAT6STP, especially, is really well shielded: Each twisted pair is shielded as a pair, and then all the shielded pairs are shielded again.  It's still cheap.

WB2WIK/6

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W8JI
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Posts: 9296


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« Reply #5 on: October 28, 2007, 02:10:44 AM »

Hi Greg,

SWR is not an issue at all, but common mode currents can be an issue. Common mode currents are caused by improper balance of the feedlines. In other words if you fed a balanced or not perfectly UNbalanced antenna from the coax without a good balun you could have current flowing down the outside of the coax shield, and that could couple. It really has nothing to do with SWR which is a parameter INSIDE the coax.

In a practical application we run about 35 feet of CAT5 next to transmission lines in my contesting barn. The spacing is several inches or less. I don't give it a second's thought about interaction even running 1500 watts because the field from the antennas several hundred feet away is much stronger than any cable radiation from the feeders. But of course my feedpoints are all well-designed and the cables are all properly grounded at the entrance.

If you do have problems they can be fixed easily with a toroid core or two.

I have a 2" diameter #67 mix toroid with several turns of the CAT5 positioned on each end on the computer cables. I felt it totally unnecessary to use shielded CAT-5 since any common mode currents are largely unaffected by the shield. It is impossible to shield for the effects of common mode, and common mode will always be the primary issue.

You can see my wiring layout at:

http://www.w8ji.com/contest_station_w8ji.htm

The blue wires are the CAT cables. We use some CAT5 and CAT3 for antenna switching cables also.

73 Tom
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WA3SKN
Member

Posts: 5477




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« Reply #6 on: October 28, 2007, 08:02:53 AM »

RF shouldn't bother the Cat 5 cable, but the square waves on the Cat 5 cable could cause noise problems to your rigs. This is trial and error here.
 If you develop a noise problem, you know where to look!
Most installations with coax don't pose a problem.

-Mike.
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WD6S
Member

Posts: 19




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« Reply #7 on: November 05, 2007, 12:41:34 PM »

I have run CAT 5 lines in tow separate locations, one next to a 2 meter radio which is also where my cable modem and network switch is located- no problems there.

I also have CAT 5 running into my shack (which is in a separate shed- a real shack) with multiple HF and 2 meter radios and I have no problems there either with interference either way.

Of course I do not use more than 100 watts for anything, so I can't speak for higher power.

Bob
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