Ground radials on the roof?

Radial systems on a roof are no different from a radial system in the ground or laid on the surface of the ground. Difference is that for lightning protection, you need to run a ground line from your elevated system to Earth ground and into a ground rod. This can be done through a plumbing vent pipe which would probably be better as that vent pipe would be surrounded by the structure material and may provide some attenuation to any emitted signal from the vent pipe. Adding a choke between the vent pipe and the ground radial system will further reduce any chance of the vent pipe from radiating. Without it, it might produce an excessive field strength even with the vent pipe being surrounded by building material.

RFB

Thanks as always RFB!

So in the case of a radial roof system, what do folks use and how do they keep it from blow around without penetrating the roofing surface.

I suspect on a roof radial install, using lightweight 16 gauge wire might be the best and easiest install type. Windblown cables would quickly create a mess though.

Would the idea be to run these to the eaves and tack them down there into say wood?

What do you think?

My ATU was fairly well centered on my roof, mounted atop the TV antenna about 5 feet above the roof.

From the ATU, my radials ran in opposite directions, equal in length. The ends were attached to the spikes holding the gutter to the overhang. The radials were insulated from the gutter.

There were 6 radials fanned out equal and opposite each other.

Thank mram!

Any idea of what you used for the radials? Gauge, twisted or solid wire, coated or uncoated.

Easier to try the true and tested than do things in improvised error prone manner.

"Would the idea be to run these to the eaves and tack them down there into say wood?"

It might be a good idea to make a windsock and determine which way the prevailing winds come in at so you can get an idea of where the most tacking down would have to be.

You don't want to use too light of wire as they can slap and bang in the wind against the roof and end up being torn apart. But at the same time you don't want too heavy of wire as that really doesn't improve anything but add to the cost.

Typical stranded and insulated hookup wire of the 16 gauge or slightly larger is good. Use blotches of weather silicone every foot or so along the wire's length to help secure it, and tack down at the ends either with a larger blotch of silicone or tack nails if there is enough wood to do so without punching a hole through the roof which would cause leaks.

One roof top ground system I set up years ago used eye hooks with threaded ends. I threaded those into the overhang and attached the ground radial wires to the eye hooks. Each eye hook were of the type that had the hard plastic ring inside the hook eye. I simply tied the wire in a knot through the eye of the hook and then took weather silicone and filled the eye with the silicone and made sure the end of the wire was inside that blotch of silicone..sealing it from weather corrosion.

RFB

Winds here are gusty and from all directions. It's an effect of being above common grade and being at the end of about 200 feet of open space. Deal with the mess it brings all the time with windblown yard stuff.

I have a good amount of experience weatherizing and siliconing things. Eye hooks I use all the time. Just not in this application. Fortunately, the eves and edges of roof are wood, so fairly simple to install aside from borrowing a very big ladder (i.e. 35-40 footer).

The 16 gauge wire gets pricey quick. Big uptick in wire costs in past few years. Need about 20 ft for each radial arm. Reading that folks recommend at minimum a dozen radials and actually more like two dozen. At 24 radials = 480ft = 500ft roll. Doable 🙂

24 radials seem good or overkill?

If you've got a shingled roof, you could carefully pry up the some tabs of the shingles, slide the wire radials under and use a dab of asphalt roofing cement to stick the shingle tabs back down.

"24 radials seem good or overkill?"

Na not really. The more the better. Think of them as being a catch bucket for a self feeding water fountain. The bigger the catch bucket, the more water recollected from the spout.

RFB

While more is definitely better, you'll get significantly diminished benefit at over 8 radials.

And the radials need to be perpendicular to the antenna system, otherwise they will radiate (and therefore could be considered part of that antenna system).

My 6-12 foot radials were of 18 awg stranded hookup wire (some type of plastic insulation.)

Some on here have used extension cords, lamp cords, etc. One guy said he left the ends on the extension cords allowing him to just plug in more as needed.

In his Ultimate Antenna instruction PhilB has specified the recommended ground radials for a part 15 AM system:

32 to 64 ground radials at least 30-feet long.

Of course that means a total of 60-feet, counting the opposite side.

32 radials is quite a bit of wire, especially in elevated installations (i.e. roofs). Getting less concerned with the cost of radials and more concerned with managing the wire mess, wind blown potential and long term maintenance.

Big question for Part 15'ers is with their existing radial installations, what are they using for radial collar (ring around radiator to which the radial wires are attached)? I've seen a pretty common square aluminum solution widely used elsewhere, but it's pricey (i.e. $50-$100) and seems targeted at ground level installs that are also cemented in place.

Theory and experience both show...

Radials buried in the earth should be as long and as numerous as possible. An AM broadcast station typically uses 120 x 1/4-wave buried radials extending out around the tower base, spaced at 3 degree intervals.

Wires used as an elevated counterpoise can be far fewer in number than when they are buried. There are examples of successful AM broadcast stations using only 4 x 1/4-wave radial wires elevated 10-12 feet above the earth.

The groundwave fields produced when using either of those radial systems have been measured to be virtually identical, for the same tower height, applied power, frequency, and earth conductivity.

As shown in the NEC study I linked to in another thread, even two elevated radials both much less than 1/4-wavelength are still useful.

Great info Rich! Starting to understand the theory and pieces more clearly.

Would using counterpoise/radials in raised roof installation be redundant/unnecessary where mounting immediately above large aluminum roof? Or does it seem possible to still receive benefit from wiring radials along the surface of said metal roof?