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eHam Forums => Station Building => Topic started by: KJ4RWH on March 16, 2010, 04:39:31 PM



Title: Elevate coax on dark roof
Post by: KJ4RWH on March 16, 2010, 04:39:31 PM
Soon I'll be mounting a 2 meter vertical on my chimney. About 20' of the RG8 will be traveling across the dark shingles and I thought it might last longer if I could elevate the coax a couple of inches to allow air flow. Has anyone found some type of non conductive disk that the coax would pass thru like an axle to provide a standoff function?


Title: RE: Elevate coax on dark roof
Post by: KH6AQ on March 17, 2010, 05:40:53 AM
I have not heard of polyethylene coax being damaged by a hot roof. You could use Teflon coax and have no worries.


Title: RE: Elevate coax on dark roof
Post by: WB5JEO on March 17, 2010, 08:30:25 AM
Might be easier to make that run through flex plastic conduit. It's gray. It's cheap. And the ribs keep most of it out of contact with the roof.


Title: RE: Elevate coax on dark roof
Post by: W3LK on March 17, 2010, 02:03:50 PM
Soon I'll be mounting a 2 meter vertical on my chimney. About 20' of the RG8 will be traveling across the dark shingles and I thought it might last longer if I could elevate the coax a couple of inches to allow air flow. Has anyone found some type of non conductive disk that the coax would pass thru like an axle to provide a standoff function?

Waste of time. The coax radiates no heat to dissipate and it is highly unlikely that the roof will ever get hot enough to have any effect on the coax. I had runs of RG8 across an asphalt roof in downtown baltimore for about 15 years with effect upon the coax whatsoever.



Title: RE: Elevate coax on dark roof
Post by: WB2WIK on March 17, 2010, 02:09:07 PM
Just use good coax.

Its insulation is good to 80 degrees C (176 degrees F).

If your roof is hotter than that, I'd move.


Title: RE: Elevate coax on dark roof
Post by: KJ4RWH on March 17, 2010, 03:08:57 PM
Thanks fella's. I guess I was worried about nothing. Barring a lightning storm, it'll go up Saturday. Jeff


Title: RE: Elevate coax on dark roof
Post by: W3LK on March 18, 2010, 08:15:56 AM
Thanks fella's. I guess I was worried about nothing. Barring a lightning storm, it'll go up Saturday. Jeff

Not to throw water on your project, but is your chimney an active one; does it vent an active fireplace in the winter or your heating system? If so, you need to rethink the mounting. Flue gases will eat an aluminum antenna in just a couple of years (or less) and it will turn any fiberglass radome brittle to the point of crumbling in not too much longer an amount of time.

And then there's the lateral stress on a structure that was never designed for such stress.