4 ms·

This is factually incorrect, because AM is incredibly inefficient. AM receivers can be electrically simple, but unless they are well designed and have very larg

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://wsjt.sourceforge.io/wsjtx.html https://meshtastic.org/docs/introduction/ https://meshtastic.org/docs/introduction/

cogman10 2y ago
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.
- geerlingguy 2y ago
  Indeed, HD AM radio worked pretty well, but never became popular, thus stations turned off their HD transmissions one by one.
nativeit 2y ago
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…
- hilbert42 2y ago
  "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.
- jdietrich 2y ago
  You can bounce a digital signal off the ionosphere much more easily than an AM signal - see the first in my comment.
  - hilbert42 2y ago
    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.
hilbert42 2y ago
"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.
- jdietrich 2y ago
  >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.

cogman10 2y ago

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.

geerlingguy 2y ago
Indeed, HD AM radio worked pretty well, but never became popular, thus stations turned off their HD transmissions one by one.

nativeit 2y ago

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…

hilbert42 2y ago
"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.
jdietrich 2y ago
You can bounce a digital signal off the ionosphere much more easily than an AM signal - see the first in my comment.
- hilbert42 2y ago
  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.

hilbert42 2y ago

"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.

jdietrich 2y ago
>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.