These are difficult times for the commercial broadcast-radio business, both AM and FM. According to various articles, such as this one from The Los Angeles Times, listener ratings are continuing to fall, and some carmakers -- where most radio listening is done, apparently -- are considering eliminating radios in the car completely, and not even offering it as an available option. Today’s drivers don’t need old-time radio (a.k.a. "terrestrial radio") for music, weather, traffic, news, or whatever, as they have smartphone connectivity, MP3 players, satellite radio, and much more.
Despite the attempt at positive spin that this article from The Wall Street Journal tries to put on the situation (sorry, may be behind a paywall), most people hearing AM radio now get snippets of it as little more than background noise, such as when they are on a short drive or in a store; a lot fewer people deliberately turn to listen to a given show than did so just a few years ago. The only successful remaining AM stations, relatively speaking, are talk shows covering sports, politics, and religion; as a music-delivery vehicle, AM radio is pretty much dead. We’ve come a long way from top-40 radio and the “hit maker” stations of yesteryear, that’s for sure.
Ironically, putting an AM radio into a car was actually once a very big deal. Companies such as Motorola prospered by designing tube-based radios that could fit into the car’s console space, withstand the vibration, and operate from the car’s 12-VDC supply. To boost that DC voltage to the much-higher voltages needed by those tubes, an interrupter device was used to chop the DC into rough AC, after which it went to a step-up transformer and then was rectified.
Was this switching supply -- which is conceptually the same as today's far more elegant and sophisticated ones -- fairly crude? Yes, indeed. Was it effective? Also yes, and it was the only solution available. It also generated lots noise in the AM band, so it actually advanced the design and production of filter technology as well. You think you have thermal and dissipation issues? Just try designed a multitube radio to work in the console of a car.
Should we care about this sharp decline in both casual and dedicated AM radio listenership? It’s always a little sad when a system, which has served us for decades and done so much to advance technology through mass-market production and needs, fades out (here, literally and figuratively), but progress is progress. The “joy” of finding and catching those enticing and perhaps mysterious far-away stations at night, when propagation signals in the broadcast band support long-distance skip, now seems so retro and quaint. After all, you can get streaming broadcasts from just about anywhere in the word via the Internet, and without the hassles of tuning, antenna configuration, propagation fading, and many other idiosyncrasies of the wireless world between 550 and 1,600 kHz.
Even the venerable and brilliant superheterodyne architecture developed by Major E.H. Armstrong, used in all AM radios as well as nearly all other receiver signal architectures, is now seeing serious competition from zero-IF and direct-to-digital topologies. Note that Armstrong developed the superhet to improve on the vagaries of his previous topology of the super-regenerative receiver; after the superhet, he developed FM to overcome the effects of atmospheric noise on AM signals. Again, broadcast radio opportunities both drove technology and manufacturing advances in low-cost, mass-market products.
Even though AM (and to a lesser extent, FM) broadcast radio may be declining, that doesn’t mean that amplitude modulation itself is falling away. In fact, advanced data-encoding techniques use increasingly sophisticated and complex forms of AM, such as 256 QAM, to impress more data onto a given signal within a fixed bandwidth. AM radio has spurred many advances in both transmitter and receiver technology; just check out the 50 kW transmitter tubes at one end, and the amazing simplicity of a basic crystal radio at the receiving end.
Do you see any downsides to the impending demise of AM radio in cars and other venues? Will you care if your next car has no terrestrial radio? Do you know of any other technologies that have had their days of glory, and for which you feel some loss, and even a twinge of regret, that they are also on the way out?