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Title: coiling foam dialectric coax Post by: K6JEK 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? Title: Re: coiling foam dialectric coax Post by: N8ETQ 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 Title: Re: coiling foam dialectric coax Post by: WA1GFZ on October 19, 2011, 08:46:06 AM I used it in my first 4-1000A rig. It migrated and shorted.
Title: Re: coiling foam dialectric coax Post by: Jim, W5JO 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.
Title: Re: coiling foam dialectric coax Post by: K6JEK on October 19, 2011, 12:03:24 PM Thanks, guys.
Title: Re: coiling foam dialectric coax Post by: WD5JKO 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. ;) my 2 ¢, Jim WD5JKO |