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Old 05-23-2017, 10:15 PM
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Default Running coax near power cables?

In the car audio world you should run power and signal wires down separate sides of the car and try to interest at 90* angles if they need to cross, is coax similar? In addition can two coax cables be run in parallel? I'm looking at running new cables for my HAM and CB radios later this week, can they share zip ties?
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Old 05-24-2017, 07:29 AM
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Ideally there should be physical separation. The reason is the same as in car audio but with ham it's bidirectional, transmitting can couple noise onto the power lines as well as the other way. The 90 degree rule also applies. Also the length of the parallel run matters. Jamming everything together only to pass through a firewall is fine if you can spread them out under the hood and inside the cabin otherwise.

One thing to keep in mind is you're only concerned with AC for noise. DC won't generate noise nor will it be sensitive to it. IOW, if you're powering a radio with a battery you can bundle the power leads and coax if you want. It's only when you connect the battery to an alternator that they potentially become noise sources. On the flip side when you couple noise onto a battery lead in a car it only becomes an issue when there's an AM/FM radio or ECU connected to it that won't tolerate noise.

The ideal situation is that you also keep physical separation from individual coax feedlines, however they can be run in *fairly* close proximity. If you put wires and/or multiple coax touching they will couple but it only takes a few inches to reduce that in effect. It's not necessary to keep power and signal on either side of the vehicle but bundling everything together will probably cause problems. The problem is you can't say *exactly* that x inches is what you need, might be 3", might be 6".

The quality of your coax is crucial to how bad it will be. The cheap single layer RG-58 that you can see through has a terrible shielding effectiveness. Multiple layer braided or using a coax with a foil layer is quite a lot better. The upside here is that noise that couples on your coax is generally common mode, so a choke can be used to block it.
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Old 05-24-2017, 09:19 AM
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I was hoping to run both m coax cables off the tire carrier and route them in the frame of the 40 and then pop them through the firewall to the radios in my tuffy console. However, I really only desire them to be "together" inside a loom from the firewall to the radios, maybe a 3-4' run.

I could pop them each in their own wire loom but would prefer just one if possible. And iirc, I want to avoid coiling any coax to take care of extra length, correct? I think that coiling it then zip tying it in the middle to make an infinity sign is okay? I shouldn't have have much of 18' of cord left over anyway.
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Old 05-24-2017, 09:27 AM
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You can only do as much as you can in a truck with the limited space. There's ideal and then there's reality. Running them together here and there will be fine. Ultimately the quality of the coax and your workmanship will be more important than running them closely parallel sometimes.

I would use high quality RG-58 or RG-8X, for example LMR-200 or LMR-240. The standard grade stuff you get from Radio Shack or whatever has very poor shielding. I'd use better quality cable even if you weren't concern by proximity but in this case the double braid and/or foil layer will help tremendously.

If you don't want to cut your coax to length then, yes, a bowtie is better than a loop. You should just cut it to length, though.
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