New England is full of ruins. Woods everywhere are veined with stone walls, relics of an agrarian age that ended when the industrial one began. Shipping canals, which were thick with horse-drawn cargo when the Thoreau brothers rowed past them up the Concord & Merrimack Rivers, were abandoned once railroads did the same job better. Mills along canals and rivers have long since been torn down or turned into museums, stores or condos. Bypassed by cars and trucks on highways, old railroad beds have lost their easements or turned into bike trails.

So now what happens to radio and TV — two more old industries with landmarks on landscapes? I visited the subject to some degree over in Linux Journal yesterday, with What if they gave a DTV transition and nobody came? Here I want to go farther, and look at an industry we know is going to die — and to start doing it well before the end arrives.

AM radio, which operates on such low frequencies that signals are radiated by entire broadcast towers, are built as single or multi-tower “arrays” sitting on buried conductors: “ground systems” that can take up more space in soil than their towers occupy in the air above. Most of these facilities were built between the 20s and 80s. Since then scarce land and environmental restrictions have slowed their spread. I would add that available frequencies are also scarce, but that hasn’t stopped the FCC from easing rules, over and over, turning the band at night (when signals bounce off the sky to reach hundreds of miles from their transmitters) into wall-to-wall hash.

FM radio has only been around in a serious way since the 1950s. Operating on a VHF band, where the antennas themselves don’t need to be large (as they do on AM), FM does best when radiated from altitude, meaning the tops of mountains, buildings and high towers. Some of the latter grow to the legal limit of 2000 feet.

With its VHF and UHF signals, television also requires transmission from altitude. When you see a very high tower standing on landscape, or a bristle of short towers atop mountains and skyscrapers, you’re looking at sources of TV, FM or both. A huge percentage of the world’s tallest masts (a category that includes buildings and towers) stand in the U.S., and many are the full 2000-foot height. Most were built for TV stations. (Wikipedia has a comprehensive list of these. Also of tower collapses — a remarkably long list.)

The first set of these to go the way of ship canals is low-band VHF TV. That is, channels 2-6. After June 12, no antenna broadcasting on those channels in the U.S. will continue to operate. Most high-band VHF TV channels — ones operating on channels 7-13 — will also be abandoned, though a few will continue to transmit digital signals. All stations that formerly occupied channels 2-6 will move to a UHF channel (14 to 50).

Old analog TV transmitters are mostly worthless and can’t be re-purposed. (Here’s an excellent piece on that subject, from The Current.)

What I’m wondering about are the towers. The Current’s story suggests that they’re too expensive to take down (not worth enough in scrap), and that most will be re-purposed in any case.

I don’t think so.

It might be easy enough to re-purpose a few former Channel 2 or Channel 4 towers. But what happens when AM and FM transmission is obsoleted by webcasting? This hasn’t happened yet. There are many architectural and UI challenges, plus the added legal burden of copyright restrictions, which are much tougher on music broadcast on the Web than on the air (at least in the U.S.) But the end will come. The brightest writing on the wall right now is the Public Radio Tuner, a project of CPB and several public radio organizations. Last I heard (disclosure: I’m involved in the project), downloads of the free tuner for iPhone were past 1.6 million. This and other tuners, on the iPhone and other portable devices, will account for more and more listening, especially as more cell phone data plans take the ceilings off data consumption — as AT&T has already done for the iPhone.

Some have suggested that TV and FM towers can be re-purposed for cellular use, and to some degree that’s true. But cellular coverage requires many sites at low elevations, rather than a few at high elevations. As one Cisco guy told me, “they might be able to lease out the bottom 200 feet” of a tower.

Still, ends always come, and The End is in sight for over-the-air radio as well as TV. Then what?

Bonus linkage: Scott Fybush‘s amazing series of visits to broadcast towers, over many years; and a few of my own photos of transmitting sites, many shot from altitude. Also the blog and tweets of George Clark, both of which led to this digression.