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This is factually incorrect, because AM is incredibly inefficient. AM receivers can be electrically simple, but unless they are well designed and have very large and well-sited antennas, they have extremely poor practical sensitivity. Most clear channel AM broadcasters in the US operate at 50kW during the day; some international broadcasters operate at hundreds of kilowatts. AM broadcast transmitters are large and vulnerable pieces of infrastructure with little or no redundancy that require colossal amounts of power to operate effectively.

The amateur radio operators who are preparing to maintain communications "come the bomb" are moving in droves to modern digital modes, because of the huge advantages in weak signal performance - likewise for military and public safety radio. If you want to get a message through in tough conditions, it's a no-brainer to use a highly efficient modulation scheme with error correction.

AM receivers are widely available for legacy reasons, but that's about the only thing in AM's favour.

https://wsjt.sourceforge.io/wsjtx.html

https://meshtastic.org/docs/introduction/

It's range is largely due to the frequency as well, not the modulation scheme.

> it's a no-brainer to use a highly efficient modulation scheme with error correction.

And an audio codec with a good ecc scheme on top. You can shove huge amounts of data into the AM spectrum, there's no reason it should be filled with pops and fizzes.

Indeed, HD AM radio worked pretty well, but never became popular, thus stations turned off their HD transmissions one by one.

Depends on your primary goal. Digital signals don’t carry very far without significant infrastructure. “Come the bomb” quadrature encoding will not be helpful for wide area universally accessible communication…but analog signals distributed by transmitters that are still very much alive and active at every radio station (and many emergency facilities and private residences), or that can be made cheaply out of broadly available and very simple components, with wavelengths long enough to get bounced off the ionosphere, and zero dependence on large scale built infrastructure…

"bounced off the ionosphere, and zero dependence on large scale built infrastructure…"

Exactly, it seems the present generation is unfamiliar with the way traditional AM radio works. It's really worrying, as it demonstrates how very easily knowledge can be lost across only just a few generations.

You can bounce a digital signal off the ionosphere much more easily than an AM signal - see the first in my comment.

First, to your earlier point that my comment was factually incorrect and that AM is is incredibly inefficient. I was not comparing or even discussing modulation techniques here, that's a totally separate matter, in fact I agree with your comment.

The point I was making is that AM is not only simple (a crystal set/germanium diode will demodulate it) but more importantly it is the 100+ years of experience and especially the huge amount of existing AM infrastructure throughout the world including millions of car radios—including those in undeveloped countries which is important—that are key to why there's a push to maintain the service through legislation. I've already made comments to that effect in other posts so I'll leave it at that.

Second, I agree with your point here about digital signals and the ionosphere. Similarly, it's why I'm a great fan of Digital Radio Mondiale (DRM—badly named given its other meaning).

In fact, I'm upset and rather annoyed that it receives so little attention and that it's made so little penetration into HF bands but there's little I can do about it except whinge.

Unfortunately, just because something is good or better doesn't mean it gets adopted (remember VHS won out over Betamax although the latter was better, also Windows versus Linux is another comparable case). If you look at history often technical standards (and improved methods) are adopted after the event. Also, grandfathering technology is commonplace whether we like it or not. I learned this years ago when sitting on several preparatory committees for WARC/WRC and also when involved with television standards for industrial work. Things that make obvious sense technically often don't get up because of political and economic considerations—and stubbornness by those with entrenched views. It's a big problem (arguments over standards are common, are often heated, and invariably messy—and often the outcomes end up overly compromised).

That brings me back to my earlier point about AM, other systems are better but other factors stop them from being universally adopted.

"This is factually incorrect, because AM is incredibly inefficient."

What have said that's factually incorrect (please be specific)?

Why is AM is incredibly inefficient?

People used AM very effectively throughout the 20th Century to communicate around the world. My example of communicating half way around the world on three watts of AM is hardly inefficient. Frankly, it's truly remarkable.

What I was talking about had nothing to do with modulation schemes. It had to do with the ease and practicability of AM radio especially when technical support infrastructure is minimal and that includes expertise/technical personnel (there many no be any in certain emergencies).

Incidentally, digital modes have their place and I've no argument with that, but I'd take issue with your broad statement about "the huge advantages in weak signal performance". Would you explain precisely what you mean? The info in your links isn't helpful here.

BTW, I got my amateur ticket when I was 15 in high school many decades ago, I'm very familiar with how the amateur movement works and with the tech that we use.

>What have said that's factually incorrect (please be specific)?

This:

"AM radio communications is the best value for money of any communications system outside of telegraphy (wired or wireless). It's cheap, simple, easy to construct, and it's scalable to any size (and transmission distance) that's needed."

AM is technically simple, but it isn't cheap, practically simple or easy to construct. You need to throw an enormous amount of power into the air relative to a more efficient mode, which means big transmitters, big masts, big power bills, big repair costs. AM broadcast stations are being closed down at a rapid rate because they're very expensive to run and maintain. That infrastructure is inherently vulnerable to whatever end-of-the-world scenario you might be worried about.

You can get a very long distance contact on AM, but you need good propagation conditions and a great deal of luck; a suitable digital mode will do that on a long wire hanging out of an apartment window during a solar minimum.

>Why is AM is incredibly inefficient?

The carrier signal and half the sideband is completely wasted power, hence SSB. The majority of the power going into your antenna carries no information whatsoever, it just compensates for the crudeness of the receiver. With AM there is a 1:1 relationship between the SNR at RF and baseband; the only way to overcome noise local to the receiver is to throw a louder signal out of the transmitter.

Even FM has an advantage here, but a digital mode can operate on incredibly tight SNR margins. The modulation scheme can run pretty close to the Shannon-Hartley limit, and (if you need voice) you can drastically reduce your data rate with a good voice codec. If you don't need voice, then you can use a very data rate and work on incredibly low (or even substantially negative) SNR. Spectral efficiency and power efficiency are two sides of the same coin.

As I said in my original comment, AM receivers are commonplace, but that's the only thing going in AM's favour. If we were to design a communications system of last resort today, there are a multitude of better options. Relying on the existing AM broadcast infrastructure for emergency communications is mostly wishful thinking if you compare that to a really serious system like Japan's J-alert.

"As I said in my original comment, AM receivers are commonplace, but that's the only thing going in AM's favour."

Thanks, you're correct. And as I've said elsewhere that's why it's being mandated.

The problem is that radio stations typically don't have anyone in the booth most of the time, if ever:

https://en.wikipedia.org/wiki/Minot_train_derailment

> The Minot train derailment occurred just west of Minot, North Dakota, United States, on January 18, 2002, when a Canadian Pacific Railway freight train derailed, spreading ammonia gas across the city, delaying rescue operations. The cause was found to be small fatigue cracks in the rails and joint bars, not detectable by the inspection routines then enforced by Canadian Pacific.

[snip]

> Because it was the middle of the night, there were few people at local radio stations, all operated by Clear Channel with mostly automated programming. No formal emergency warnings were issued for several hours while Minot officials located station managers at home. North Dakota's public radio network, Prairie Public Broadcasting, was notified and did broadcast warnings to citizens.

And Minot is one of the bigger cities in North Dakota.

Seems like it would not be difficult to pass a piece of legislation mandating some form of registered on-call responsibility for the licensees of these spectrum bands?

A lot of things that aren't hard never, in point of fact, get done.

"The problem is that radio stations typically don't have anyone in the booth most of the time, if ever:"

Agreed, it's a serious issue, and the first thing one notices about prerecorded and netwoked programs is the lack of spontaneity and liveliness of the content (personally I don't like stations that are run like this).

This, of course, is a regulatory matter. There's no reason why programs cannot be interrupted by an actual human in such emergencies, even if not a professional announcer, an emergency worker or police perhaps.

You've made a very solid case for AM radio continuing to be a relevant technology today and far into the future.

I do not, however find that to be a compelling argument for mandating its inclusion in cars. While market forces may be inadequate for driving crash safety, emissions, or fuel economy standards, they seem very well-suited to determining whether cars include AM radios. I suspect the answer will be that most car buyers don't care, and a cheap portable receiver is an adequate solution for many who do.

It's like this. AM is the lowest common denominator and that's why it's being mandated. There's nearly 100 years of experience of having AM radios in vehicles, it's easy, very cheap and it works. Everyone knows how it work and millions still listen to it.

Even if you never use the AM radio in your car someday someone else may do so to get emergency info (it has a much longer range than FM).

BTW, most of my radio experience has been in FM broadcasting, so I'd naturally choose that as a better quality broadcast medium. But we're not talking about that here, but rather the fact that AM radio is the LCD for a multitude of reasons.

Incidentally, I've also worked on the transmission side of television and I've been involved with spectrum management from a policy perspective. What I've notice in these posts is the tendency to dismiss AM simply because people have become unfamiliar with it given the many media options available today.

What people forget or have never understood is that to get that high quality video and sound on your smartphone, or on your widescreen OLED TV requires a huge amount of very complex infrastructure, and it takes many people and many organizations to do so. Only the slightest thing has to go wrong and the whole edifice will come crashing down. An idiot, terrorist and or natural disaster can kill it in an instant, whereas the low tech widely distributed AM TX network is much, much harder to bring to a halt. We saw this on many occasions in WWII, there were many instances where cities were left in ruins but the AM broadcast from those cities were either left intact or gotten up and running again within only a few hours. Again, that's what this whole discussion is about and why AM car radios are being mandated.

As I mentioned elsewhere, heaven help us come the next Carrington Event (which it will), none of that lovely media infrastructure will be left standing. Similar scenarios can result for certain emergency situations. When all communications fail then AM radio will be by far the easiest to reestablish, and with millions of cars having an AM receiver that will have services up and running much faster.

I know AM is not fashionable but it works and it's easy to establish, same can be said for sewer pipes but we don't chuck them away because they're not fashionable or because they're low tech.

You just about have me convinced to buy a battery-powered AM radio, but I think we might have very different thresholds for mandating things.

AM is awful and outdated. The only benefits it currently has, aren't actually related to the amplitude modulation, but simply a property of the reserved frequency bands it uses.

"AM is awful and outdated."

This, simply, isn't the issue.

If we're going to talk about emergency communications, let's go full send. "Come the bomb", I'm thinking I'm going to want short wave, 10M (citizens band), FRS. Rather than relying on a few huge transmitters, I'm imagining we'll want to make use of the ham radio equipment that is distributed around the world.

Honestly, in my 35+ years of driving, I've used CB/FRS way more often than AM.

Mind the difference between AM and SSB (which may be considered a subset of AM). The efficiency increases with SSB, when compared to usual AM.

I think that ssb is great but it targets bands of radius around you

I'm not sure AM has the same issues

Here's a chart that illustrates skywave bounce

    2 MHz 200-400 miles
    4 MHz 400-600 miles
    6 MHz 600-1,200 miles
    8 MHz 800-1,600 miles
    12 MHz 1,200-2,400 miles
    16 MHz 1,600-3,200 miles
    22 MHz 2,200-4,000 miles plus
    26 MHz unpredictable during our solar cycle minimum

But of course any of that is completely independent of whether using SSB or not. Modulation used doesn't really change wave characteristics to such significant extent. It's just that SSB is much more effective, this way or another, so it will probably get used in cases like that.

"Modulation used doesn't really change wave characteristics to such significant extent,"

True, except when the ionosphere is changing rapidly and phases change across the bandwidth (as in fading). SSB helps and it's really great for narrow band comms but without the carrier the demodulated audio has pitch problems. Not an issue for basic comms but it is if audio has to be on frequency.

SSB reduced carrier and synchronous detection is another solution.

My internet was out recently and I realized I don’t even have a radio (or TV antenna) in my house. Just cut off from the world when the internet is failing.

I went out and bought a radio in case that awful day comes.

> Years ago during a sunspot maxima, I watched a friend of mine located in NSW Australia talk to someone in California on 27MHz AM using only three watts of power (from a handheld CB radio) and using only a whip antenna.

This example makes me think that these wavelengths will be heavily congested in the event of a major global, or even local, disaster.

(I know next to nothing about radio)

I imagine this would depend on who can transmit "louder"? In the case of a disaster, that would likely be emergency services of some kind

Yes and no; think of a loud room where everyone is shouting because that's the only way to be heard due to everyone shouting.