Many of the currently available electric vehicles (EVs) on the market have a wonderful array of bells and whistles you won't get in a gas-powered car, but some new EV owners are surprised by the lack of one feature: an AM radio (referred to by radio amateurs as "ancient modulation" because it was the first radiotelephony technology to be invented).
Now for most younger readers, an AM radio is not going to be missed. While radio in general still has its uses for mobile platforms that can't yet conveniently connect to the Internet (although this problem will eventually go away too), AM radio is the oldest and lowest-quality medium in the broadcast hierarchy. Consequently, much of its programming is devoted to talk shows, sports, and the kind of music that doesn't suffer much from the thunderstorm crackles, power-line buzzes, and night-time fading that AM radio is subject to. Nevertheless, millions of people listen to AM stations across the U. S. and in other countries, and probably a majority of them do it in their cars.
So why do many EV makers leave out the AM-radio feature? It has to do with an obscure branch of electrical engineering called "electromagnetic interference" (EMI).
EMI studies how electric, magnetic, and electromagnetic fields and their related voltages and currents go from one electronic subsystem (quaintly sometimes called the "aggressor") to another subsystem (called the "victim") and mess up the victim's functioning somehow. As our world becomes increasingly digital, casual experience with EMI is no longer common, as the characteristic of most digital systems is to work flawlessly until the interference reaches a certain threshold. Then the whole thing collapses and you get nothing.
Analog systems—the old analog TV that went away about 2009, conventional AM radio that is still with us, and to some extent, FM radio—are different. As the interference gets stronger, if you were watching an analog TV picture, you'd first see some little random black specks here and there, then solid rows of them, then wider bands and the sound would start to feature a buzz-saw noise, and finally you'd lose everything in a kind of snowstorm (video noise was in fact called "snow".)
AM radio is the same: a few pops in the speaker here and there, then a steady buzz, and finally the signal is overwhelmed.
So why don't most EVs have AM radios? Because the thing that makes EVs go is kilowatts of electric power, hundreds of volts at dozens of amps, being switched on and off thousands of times a second. And the efficiency of the electronics depends on how fast those switches work.
Unfortunately, switching large amounts of power on and off very fast generates tons (metaphorically speaking) of energy that runs roughshod through the whole AM broadcast spectrum, which ranges from 540 kHz to 1600 kHz. And a typical EV is just full of such currents, voltages, and magnetic fields, because the currents run through cables by necessity from the battery through the control electronics to the motors.
I've never tried the experiment, but if you had a Tesla or other EV running on a test stand, and you got a little cheap portable AM radio, tuned it to an empty spot in the band, and moved it close to the car, you would in all likelihood be greeted with a banshee set of howls and growls that would be a good soundtrack for a horror film.
Most of the energy thus produced is probably in the form of near-field magnetic fields. These don't radiate very far (that's why I've been passed by many Teslas on the road while listening to an AM station and never noticed a problem), but within a few feet, which is where you are when you try to put everything into one vehicle, they can be quite intense. And in contrast to electric fields, which are fairly simple to shield against with conductive screens, magnetic fields are very hard to enclose and shield against. It takes special types of magnetic metals that are (a) expensive, (b) fragile, and (c) hard to shape, as they are usually supplied in the form of thin tapes that have to be hand-wrapped around the thing to be shielded.
Despite what the automakers say, it would be possible to make an EV that wouldn't interfere with an AM radio on board. Take a standard EV to any big military contractor and tell them what you want. They'll put a bunch of EMI experts to work, and they'll redesign the whole vehicle. It'll probably weigh another few hundred pounds when they're finished and cost twice as much as it did before they went to work, but you'll be able to play your AM radio and drive at the same time.
See the problem? That's one of the reasons the EV makers have just quietly dropped the AM radio, because it would mess up everything else if they put it in and made it work.
I don't see any good outcomes of this problem for standard AM broadcast services. There's something called HD radio, as well as several other competing digital-radio services. The basic idea is to use the allocated FCC frequency band granted to a station (plus maybe some parts of the adjacent channels) and stick a sophisticated orthogonal-frequency-division-multiplexed digital signal in there to carry as many as four audio channels. This is being tried both with AM and FM, but I suspect the digital AM is wrecked just as thoroughly by EV EMI as the conventional AM is.
So the alternative that at least one article posed, is to hope that in your metropolitan area, your favorite AM signal is also being carried by an HD-radio FM station and you can pick it up that way. FM signals use much higher frequencies (88-108 MHz), which are much less affected by the electromagnetic trash that EV power electronics puts out.
But I just went to the HD radio website and checked, and poor little San Marcos, halfway between San Antonio and Austin, doesn't have any HD radio signals. Dallas-Fort Worth is another matter.
So it may be that AM radio for cars, at least the old-fashioned kind, may go the way of buggy-whip holders on automobile dashboards. Nobody missed those then, and maybe nobody much will miss AM radio in the future.
Sources: Numerous articles are available on the absence of AM radio in EVs, and I referred to this one: https://www.motorbiscuit.com/am-radio-absence-why-evs-dont-have/. I also referred to the HD radio website https://hdradio.com/why-hd-radio/ and the Wikipedia article on HD radio.
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