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Author Topic: Coax ADDENDUM  (Read 845 times)
KE4IZA
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Posts: 240




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« on: January 24, 2003, 09:14:25 PM »


       I have 100' of RG-8x with connectors.  I was told if I use the whole 100' I will lose performance big time.  Is this true or can I simply coil the excess under the desk.
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WB2WIK
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Posts: 20636




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« Reply #1 on: January 27, 2003, 12:11:46 PM »

"Losing performance big time" depends on the cable's loss at the frequency, and under the condtions, you are using.

On 440 MHz, yes, I'd agree: Cut off any excess, and use only exactly the cable length required, as every extra foot actually has a little bit of measurable loss.

On 80 meters (3.5 MHz), even 100' of RG8X, if feeding a "matched" antenna (like a dipole or something with VSWR <3:1 or so), has such little loss that an extra 50' won't even be noticeable in terms of performance.

Normally, I trim all my coaxial cables to be only the length required to reach equipment, for a couple of reasons; the biggest and best reason is to maintain a neat appearance in the shack, and to prevent cables from all getting tangled together.

You know that per Murphy's Law, any two cables run anywhere near each other will tie themselves in a knot while you're not looking.

WB2WIK/6
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WA4PTZ
Member

Posts: 528




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« Reply #2 on: February 02, 2003, 08:27:28 AM »

I'd have to agree with WIK. But if you locate and
copy the specs for a type of coax, you will know
just how much loss it has at what frequency.
That way you can be informed. The "Wireman" has
such a chart and I'm sure there are many others.
73 - Tim
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WA9SVD
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Posts: 2198




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« Reply #3 on: February 08, 2003, 10:57:03 PM »

We can't really answer this unless we know the frequency where you will operate, AND the distance of the run!  If you have a 70' run, and are running 80-10M, the additional loss probably won't be enough to worry about.  If you have a 30' run, and are working 2M, then there it might be reasonable to cut the cable to the necessary length.  

    HOW long is the run from your antenna to rig, and what frequencies will you be using?
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