On Jun 10, 2012, at 7:43 PM, Jim Lux wrote: > On 6/10/12 4:24 PM, Chris Albertson wrote: >> On Sun, Jun 10, 2012 at 2:50 PM,<b...@lysator.liu.se> wrote: >> >>> ... 3m >>> of antenna cable is no problem. Antenna position is more important than >>> the exact type of antenna. I'd rather have a decent antenna at a very good >>> site, than a very good antenna at a slightly worse antenna site >> >> >> >> 3M is trivial. 30M will work fine too. >> >> I agree about the location really mattering more than anything else. What >> I did was drill a 2" hole through the roof up from the attic and push a 10 >> foot gallanvised iron plumbing pipe up. > > you would probably want appropriate flashing around that to prevent water > (and vermin) ingress. > > > The antenna sits on thop ithe >> pipe and is higher then the roof top ridge and then the cable go down the >> center of the pipe. I pipe flange on top of the pipe makes a perfect >> mounting platform. I used a timing antenna comes inside a white pointed >> plastic radome. These sell for just under $30 on eBay. Maybe it is >> coincidence or not but the four holes pin the standard pipe flange match up >> with the four holes in the bottom of my antenna and there is enough room >> inside the hole in the center for an "N" connector. It is worth getting >> the antenna "done right" because it is the most important part of the >> entire system. Those dome type antenna are worth it. the shape is >> designed to shed both bird poop, and snow. Birds can be an issue with a >> flat top antenna, no snow here. > > You probably get snow every few decades (it snowed in Malibu a couple years > ago, for instance), but I wouldn't worry about snow loads, even so. <grin> > > > HOWEVER, your scheme is going to be tricky to pass muster with the National > Electrical Code. Two aspects need attention: > You need to have a ground wire from the mast to the ground point > and > You need to have some form of ground of the coax shield at the point where > the coax enters the building. (a "listed antenna discharge unit" is the > usual way). > > > While Southern California isn't exactly the lightning capital of the world, > we do get some. A bigger concern (and the primary reason for the code > requirement) is that above ground power lines can come down and touch your > antenna. > > And someone living in a more lightning prone area is going to want to take > those precautions. > > The installations I've seen typically use the same general "pipe" scheme > (using rigid conduit, which looks a lot like pipe, but has a smooth inside > with no burrs) to a box on the roof, and then regular conduit running down > the outside of the building. Then at the point of entrance, the ground > bonding conductor goes from the conduit to ground, and there's a coax > grounding block in a box at the place where the hole in the wall is. > > > Granted, if lightning does hit, everything connected to the antenna is going > to fry, unless you have some sort of reradiation scheme to provide an air > gap. That's what we do when we test GPS receivers destined for space, where > you don't want to take the risk of killing the expensive flight hardware. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.
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