Amplitude modulation (AM) broadcast-band radio is so “old news”. In this day of ubiquitous MP3 players, streaming audio, XM and Sirius satellite, among other options, AM radio is truly an anachronism. Despite the feverish promotions of commercial broadcasters, claiming that nearly everyone in the US “listens” to AM radio for at least 15 minutes at least once a week (a very low bar, indeed), the role and need for conventional AM broadcast radio has severely diminished (although it does have a major place in emergency and disaster notification).
So it was with some trepidation at appearing very much “out of it” that I took a portable AM radio out with me last week, just to hear what was going on in this first electronic mass medium. (Let's not forget that development of AM receivers also drove a lot of technology, including the superheterodyne architecture of E.H. Armstrong, standardized and low-cost vacuum tubes, and much more.)
What I heard was not what I expected, but should have. Sure, I could pick up some stations when outdoors, but the radio's output when inside various buildings was another story. Signals were barely audible except near the window, and the background broadband noise was high. It was not a pleasant SNR situation.
But what really struck me were the specific sounds I heard. I used the radio's ferrite antenna, with its modest directionality, to localize many of the sounds and identify the source. There was the whine from the electric motor of a nearby service cart; you could judge its rpm by the pitch. There were loud snaps from switches in nearby heavy machinery. PC power supplies and display oscillators added their own noise to the mix. Laser printers provided more electronic clunks, bumps and grinds. There was splatter from cell phones in use in the area. Many I couldn't make out, some constant, some intermittent.
All in all, it was not a pretty (audio) picture. I actually felt somewhat bad for the AM radio world, given its long and honorable history and place in society. Of course, it's not the modulation that is the primary problem, although AM has very little noise immunity. It's mostly the frequency band used for broadcast AM, from about 500 to 1600 kHz, that is the problem.
I could have decided to toss the radio in the pile of semi-obsolete but still functioning electronic stuff I have. But in today's world, it's all about spin and re-positioning your assets and attributes. I took out my Brother P-Touch electronic labeler, made up a 18-point-size label that clearly announced “500 to 1600 kHz RF Sniffer”, and felt I had done the radio justice.
But maybe, in keeping with the reality, it would have been more appropriate to use my venerable Dymo label-maker? 😉
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