Those of you who are interested have probably already seen these, but just in case... Recently KMSP's replaced their primary antenna on their Shoreview tower (the taller single tower, not the twin Telefarm towers). They switched from circular to horizontal polarization. Between that and the reduced strength required for DTV (plus not running two signals after the switch), they're going to save a ton of power (88% less on the main amps, probably 90% less than the transition power). I have some other info, but I'm not sure if it should be posted on the web, so I'm not doing that for now. In any case, of course local techs/hams took a bunch of pictures of the process, and those are posted online.
Yea, antennas are basically just a metal element (or multiple elements) opposite a ground. The elements are tuned based on the transmit frequency, generally designed to achieve as much antenna gain as possible (and also be the appropriate strength/complexity/cost). The pipes are a large coax, just with pipes rather than flexible cable and air rather than a solid insulator between the two conductors.
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Wow, those pictures were sweet. I didn't realize that the antenna parts were just made out of galvanized steel. I thought it would be something a little fancier. Do you know how those things work? I'd imagine the copper pipe/conduit things transmit power to the arrays but that's the best I can guess.