The only pipes I know of that stick out of roof tops are plumbing-stack vent pipes, and I don't think they are always metal nor are the sections electrically bonded, I think they have something like glue or putty sealing the joins.
If an electrically sound grounded pipe stuck out of the roof it would be a lightning rod.
But I am not a roofing expert.
slight recap of where i was at: i had left one radial extra long to drop over the side of my house so i could attach it to my grounding rod. with it attached to the grounding rod i could not get past 3.5V and with it disconnected but still draped over the wall i was able to get about 11.5V.
today i cut the long radial down to the same length as the others (8ft) so that it is on my roof. immediately my voltage jumped up to 14V.
why is that? and what exactly does the voltage in this situation indicate? is it the amount of power being coupled to the antenna? and if so is higher always better?
edit: i had adjusted the radials and checked the voltage at about 2:30pm today. i just checked the voltage again (9:30pm) and its back down to 10.5V. is it possible for the antenna tuning to drift throughout the day or is it more likely i was somehow making a faulty reading earlier today?
My radials don't hang over the side of the roof. They extend straight out from the base, equally spaced around the base.
I don't have a separate earth ground on the system. Rather, the ATU grounds through an inline coax protector near the entrance to the house.
The coax couples to the tuner through a toroid transformer which I think isolates the coax sheild from the ATU common ground. If that is so, the radials are not tied to earth ground through the coax sheild.
At the risk of thread-jacking, I'm curious to know what the effect would be with the same setup dietnews describes, but mounted on a sheet metal roof? While the ideal may be ground mounting with radials, not every situation will allow ground mounting. Since the relevant section of Part 15 refers to the "ground lead" (FCC's words) as being part of the overall 3M antenna length, what if a base-loaded antenna as described in this thread were to be mounted on a second story metal roof with a short ground lead attached directly to the roof itself? Inquiring minds, etc.