>What have said that's factually incorrect (please be specific)? This: "AM radio communications is the best value for money of any communications system outsi

>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.