After electromagnetic radiation leaves the legal domain of the ITU, its behavior becomes even more remarkable, as it segues into infrared, then visible light, then ultraviolet, Xrays, gamma rays and cosmic rays.
From the point of view of physics, there's a strangely arbitrary quality to the political decisions of the ITU. For instance, it would seem very odd if there were an international regulatory body deciding who could license and use the color red. Visible colors are a form of electromagnetism, just like radio and microwaves. "Red" is a small piece of the electromagnetic spectrum which happens to be perceivable by the human eye, and yet it would seem shocking if somebody claimed exclusive use of that frequency. The spectrum really isn't a "territory" at all, and can't really be "owned," even though it can be, and is, literally auctioned off to private bidders by national governments for very large sums. Politics and commerce don't matter to the photons. But they matter plenty to the people who build and use towers.
The ITU holds regular international meetings, the World Administrative Radio Conferences, in which various national players jostle over spectrum usage. This is an odd and little-recognized species of diplomacy, but the United States takes it with utter seriousness, as do other countries. The resultant official protocols of global spectrum usage closely resemble international trade documents, or maybe income-tax law. They are very arcane, very specific, and absolutely riddled with archaisms, loopholes, local exceptions and complex wheeler-dealings that go back decades. Everybody and his brother has some toehold in the spectrum: ship navigation, aircraft navigation, standard time signals, various amateur ham radio bands, industrial remote-control radio bands, ship- to-shore telephony, microwave telephone relays, military and civilian radars, police radio dispatch, radio astronomy, satellite frequencies, kids' radio-controlled toys, garage-door openers, and on and on.
The spectrum has been getting steadily more crowded for decades. Once a broad and lonely frontier, inhabited mostly by nutty entrepreneurs and kids with crystal sets, it is now a thriving, uncomfortably crowded metropolis. In the past twenty years especially, there has been phenomenal growth in the number of machines spewing radio and microwave signals into space. New services keep springing up: telephones in airplanes, wireless electronic mail, mobile telephones, "personal communication systems," all of them fiercely demanding elbow-room.
AM radio, FM radio, and television all have slices of the spectrum. They stake and hold their claim with towers. Towers have evolved to fit their specialized environment: a complex interplay of financial necessity, the laws of physics, and government regulation.
Towers could easily be a lot bigger than they are. They're made of sturdy galvanized steel, and the principles of their construction are well-understood. Given four million dollars, it would be a fairly simple matter to build a broadcast tower 4,000 feet high. In practice, however, you won't see towers much over 2,100 feet in the United States, because the FCC deliberately stunts them. A broadcast antenna atop a 4000-ft tower would hog the spectrum over too large a geographical area.
Almost every large urban antenna-tower, the kind you might see in everyday life, belongs to some commercial entity. Military and scientific-research antennas are more discreet, usually located in remote enclaves. Furthermore, they just don't look like commercial antennas. Military communication equipment is not subject to commercial restraints and has a characteristic appearance: rugged, heavy-duty, clunky, serial-numbered, basically Soviet-looking. Scientific instruments are designed to gather data with an accuracy to the last possible decimal point. They may look frazzled, but they rarely look simple. Broadcast tower equipment by contrast is designed to make money, so it looks cheerfully slimmed-down and mass-produced and gimcrack.
Of course, a commercial antenna must obey the laws of physics like other antennas, and has been designed to do that, but its true primary function is generating optimal revenue on capital investment. Towers and their antennas cost as little as possible, consonant with optimal coverage of the market area, and the likelihood of avoiding federal prosecution for sloppy practices. Modern antennas are becoming steadily more elaborate, so as to use thinner slices of spectrum and waste less radiative power. More elaborate design also reduces the annoyance of stray, unwanted signals, so-called "electromagnetic pollution."
Towers fall under the aegis of not one but two powerful bureaucracies, the FCC and the FAA, or Federal Aviation Administration. The FAA is enormously fond of massive air-traffic radar antennas, but dourly regards broadcast antennas as a "menace to air navigation." This is the main reason why towers are so flauntingly obvious. If towers were painted sky-blue they'd be almost invisible, but they're not allowed this. Towers are hazards to the skyways, and therefore they are striped in glaring "aviation white" and gruesome "international orange," as if they were big traffic sawhorses.
Both the FCC and FAA are big outfits that have been around quite a while. They may be slow and cumbersome, but they pretty well know the name of the game. Safety failures in tower management can draw savage fines of up to a hundred thousand dollars a day. FCC regional offices have mandatory tower inspection quotas, and worse yet, the fines on offenders go tidily right into the FCC's budget.
That orange and white paint costs a lot. It also peels off every couple of years, and has to be replaced, by hand. Depending on the size of the tower, it's sometimes possible to get away with using navigation- hazard lights instead of paint, especially if the lights strobe. The size of the lights, and their distribution on the tower structure, and their wattage, and even their rate and method of flashing are all spelled out in grinding detail by the FCC and FAA.
In the real world -- and commercial towers are very real-world structures -- lights aren't that much of an advantage over paint. The bulbs burn out, for one thing. Rain shorts out the line. Ice freezes solid on the high upper reaches of the tower, plummets off in big thirty- pound chunks, cracking the lights off (not to mention cracking the lower-mounted antennas, the hoods and windshields of utility trucks, and the skulls of unlucky technicians). The lights' power sometimes fails entirely.
And people shoot the lights and steal them. In the real world, people shoot towers all the time. Something about towers -- their dominating size, their lonely locales, or maybe it's that color-scheme and that pesky blinking -- seems to provoke an element of trigger-happy lunacy in certain people. Bullet damage is a major hassle for the tower owner and renter.
People, especially drunken undergraduates in college towns, often climb the towers and steal the hazard lights as trophies. If you visit the base of a tower, you will usually find it surrounded with eight-foot, padlocked galvanized fencing and a mean coil of sharp razor-wire. But that won't stop an active guy with a pickup, a ladder, and a six-pack under his belt.
The people who physically build and maintain towers refer to themselves as "tower hands." Tower engineers and designers refer to these people as "riggers." The suit- and-tie folks who actually own broadcasting stations refer to them as "tower monkeys." Tower hands are blue-collar industrial workers, mostly agile young men, mostly nonunionized. They're a special breed. Not everybody can calmly climb 2,000 feet into their air with a twenty- pound tool-belt of ohmmeters, wattmeters, voltage meters, and various wrenches, clamps, screwdrivers and specialized cutting tools. Some people get used to this and come to enjoy it, but those who don't get used to it, *never* get used to it.