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coiling foam dialectric coax




 
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Author Topic: coiling foam dialectric coax  (Read 1022 times)
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K6JEK
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RF in the shack


« on: October 18, 2011, 11:56:07 PM »

I  have always avoided making coax coil choke baluns with foam dielectric coax.  I think I read somewhere the center conductor will migrate.

Am I right about this or can I actually coil up the LMR-400 ultraflex I got my hands on at the feed point of the hexbeam?
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N8ETQ
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Mort


« Reply #1 on: October 19, 2011, 05:04:21 AM »


     It's true, The term I heard was "Cold Flow". There should be a
"Minimum Bend Radius" specified that if not exceeded it wont
happen.  Your mileage may vary.

GL

/Dan
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WA1GFZ
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« Reply #2 on: October 19, 2011, 08:46:06 AM »

I used it in my first 4-1000A rig. It migrated and shorted.
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Jim, W5JO
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« Reply #3 on: October 19, 2011, 09:21:40 AM »

Normally the bend ratio is ten times the diameter of the wire.  I would not use foam coax for this purpose.
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K6JEK
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RF in the shack


« Reply #4 on: October 19, 2011, 12:03:24 PM »

Thanks, guys. 
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WD5JKO
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WD5JKO


« Reply #5 on: October 19, 2011, 06:20:32 PM »


I agree with the comments and recommendations. Still if the coax is out of the sun, exceptions to the rules can work. I have a 10' piece of Radio Shack RG-8X from the shack to the base of the antenna where I have a shorting knife switch. I take that coax 1' from the knife switch, and wound 6 turns through a 2" OD ferrite toroid to make a common mode choke. After about 3 years it is still working, and I've at times ran legal limit power with non-perfect SWR. Oh, antenna got a direct hit by lightning too, and vaporized part of my feedline to the knife switch. That tight radius turning around the 'roid' has yet to fail.  Wink

my 2 ,

Jim
WD5JKO
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