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In my country (Germany) we have frequency-modulated (FM) and amplitude-modulated (AM) radio broadcasts. However, the reality is that no one ever listens to the AM since you just don't hear anything (I don't need to explain to you the downsides of amplitude modulation). :)

So, I asked myself why the AM part is still active? Does amplitude modulation have any huge advantages over frequency modulation that it's worth keeping the hardware alive?

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    \$\begingroup\$ What country are you from? In the United States we have quite a lot of emergency and talk radio stations operating in the AM bands. \$\endgroup\$ – Adam Haun Sep 6 '16 at 6:05
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    \$\begingroup\$ @OddDev Do note that Germany actually shut down medium-wave AM stations and the long-wave broadcast station it has is transmitting in French. \$\endgroup\$ – AndrejaKo Sep 6 '16 at 6:32
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    \$\begingroup\$ @OddDev: some clarification: The German word "Radio" is better translated into English by the word "broadcast". You probably don't mean "AM radio" but "AM broadcast". "Radio" in English means any form of communication via electromagnetic waves (in a certain frequency range); in German that's called "Funk". I guess you didn't mean to say that in Germany almost nobody uses "AM Funk" (see Adam Haun's comment above. Another example: also Aircraft Radio ("Flugfunk") uses AM; even in Germany). \$\endgroup\$ – Curd Sep 6 '16 at 8:01
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    \$\begingroup\$ Dunno if that's an Americanism, but in British English we would always use "AM radio". "Radio" is the normal word for audio-only transmissions over the air, not "broadcast". \$\endgroup\$ – patstew Sep 6 '16 at 11:15
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    \$\begingroup\$ Not a full answer, but AM Radio broadcasting is alive and well in Australia, where you want radio signals to cover vast, vast almost empty regions where the costs of putting FM transmitters to cover the same space is not economical. \$\endgroup\$ – Mark Henderson Sep 6 '16 at 19:46
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In a nutshell: One antenna will give you a usable radius of 100...1000 km, depending on the power used.

In Germany, for the example of my favored news station Deutschlandfunk, we used to have two long-wave AM stations (153 and 207 kHz, IIRC), and I do miss them every once in a while. The one at 207 kHz covered pretty much all of Southern Germany, and while I admit that the quality was low (as in: landline telephone-ish low), you could listen to the program with no trouble, anywhere in your house, and understand every word well.

Now, for terrestrial distribution, they just use FM, which works in a few small places only, or you could try DAB+, and I'm not sure if the latter works in all places. I do miss the robustness and the beautiful simplicity of long or medium wave AM.

It's not so much the type of modulation (AM vs. FM). It's the low-ish frequencies that tend to work well over wide areas and even through big walls, for example if you're downstairs.

It's not true that no one ever listened, and in contrast to North America, for example, Germany used to have only very few good stations on AM in the decade before they pulled the plug on it, which gives you another very important reason why few people listened.

A personal note: It twists my stomach to see how AM has already vanished, and to know that some want to abandon analog FM as well.

If you were to get cynical, you could argue there is some strong political will to seriously srew up anything terrestrial for good, at least in Germany. A bit off-topic here, and a rant, but terrestrial TV broadcasting shows you how bad it can become, and it's a fine example of unclever engineering: Analog terrestrial TV was shut down not long ago, in the early 2000s, with DVB-T as a replacement. Soon, (mostly private) stations stopped broadcasting on DVB-T, and now, DVB-T2 is about to be introduced, and of course, it's not backwards compatible to DVB-T, so any DVB-T receiver will be a piece of useless junkTM very soon. Considering the beauty of analog TV, this is sickening. There was black-and-white TV. Then they figured out how to put color into the signal while black-and-white receivers would still decode black-and-white and the new color TV signal, and color TV receivers would decode old black-and-white signals just as well as new color TV signals. Then, they put all other sorts of fancy stuff into the signel (stereo, videotext, ...) and everything was still forward and backward compatible. That's what I call good engineering, even more so if you put it into the context of its time and consider how advanced things were with respect to what was possible with the available technology.

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    \$\begingroup\$ Thanks for your input! I'm mid-20 and for me the AM button always was just something to gain murmur :) \$\endgroup\$ – OddDev Sep 6 '16 at 6:29
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    \$\begingroup\$ The point about the beautiful engineering of analog TV is something I agree with totally!! \$\endgroup\$ – bobby Sep 6 '16 at 8:02
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    \$\begingroup\$ +1 for the rant on the transition to digital. In Austria terrestrial TV was also switched to DVB-T. And since then, we have digital artefacts in our TV. Even drop-outs, which is heavily annoying when watching sports, such as skiing or ski-jumping. There, a second outage is not cool. The DVB-T2 story also showed us, that planned/technical/functional obsolescence is now a thing with TVs too, not only with smart phones and other gadgets. Also, building an AM reciever with little more than an antenna, a diode and head-phones is a very illustrative experiment in an electronics class. Sadly, gone. \$\endgroup\$ – Dohn Joe Sep 6 '16 at 9:18
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    \$\begingroup\$ Good that you mention it. Common analog standards, such as AM and FM radio allow you to distribute propaganda. Apart from the example of FM4, West Germany installed powerful sending stations in the east to provide Western German TV for the people of East Germany. Imagine this in the age of DVB-T and DVB-stalin? With the common analog standard for TV and radio West Germany could always claim, that this was not intentional. If West Germany installed DVB-stalin senders, which are not in use in the west, it would clearly be a deliberate act. So much for plausible deniability. \$\endgroup\$ – Dohn Joe Sep 6 '16 at 10:55
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    \$\begingroup\$ As for DVB-T receivers becoming useless tech junk: If you are reasonably lucky, your receiver will come with a tuner supported by the RTL-SDR project. Lo and behold, you have gained yourself a free Software Defined Radio receiver! :) You can even find software decoders for DAB+ that work with RTL-SDR dongles! \$\endgroup\$ – AdrianoKF Sep 7 '16 at 7:38
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Besides that also in Germany you can very well listen to AM stations, although the transmissions may not be as crisp clear as wide FM stations. There are several reasons that come to my mind why they might still operate:

  • Old AM equipment may just still be there and function, and investing in replacing with FM is prohibitively expensive
  • An FM frequency slot may not be available or the license be too expensive (FM is done usually on quite different frequencies)
  • The range where you can receive (especially at night) can be many times as big as for FM, making reaching the same audience difficult to expensive to impossible (depending on the range)
  • For political reasons you want to be received in other countries, but can not output that much FM power
  • You want to bring radio of your language to a far away different country, but can't afford the usually many times higher prices FM license
  • Sometimes an AM station is just transmitting the same "data" as some FM station, just for reachability or similar reasons
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    \$\begingroup\$ AM and FM are methods of signal modulation. MF, HF, VHF are frequency ranges. For broadcast radio, AM is commonly used in MF and HF, and FM is commonly used in VHF, but there's nothing saying it has to be that way. Though FM in MF in particular comes with its own set of challenges because of FM's relatively wide RF signal bandwidth, though you can cram a FM signal into about the same bandwidth as an AM signal and get roughly the same fidelity as with AM... (6 kHz AM and 6.25 kHz FM can both allow for about 2500-3000 Hz baseband signal bandwidth.) \$\endgroup\$ – user Sep 7 '16 at 6:03
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Others have mentioned that old equipment is often still used. Just to expand a little bit upon this: Unlike many of new technologies of today, where the lifetime of the technology itself is very short, AM radio comes from an era of long-lasting technologies. Much of the infrastructure is quite old and is still working fine.

It should be noted that this goes both ways: For broadcasters as well as for the audience. Pretty much every radio made in the last 80 or so years will be capable of receiving at least medium-wave AM stations. It's been only in the last 10 or so years that VHF-only radios have gained popularity.

The result of that is that AM is a well-entrenched technology which is difficult to update.
At first the issue was technical: good sounding FM transmissions need much more bandwidth than AM ones do, which, at frequencies where one might encounter AM radio, is simply not available.
Afterwards, with technology progress, new modulation types became available which resulted in standards such as Digital Radio Mondiale. In a standard 9-kHz European long and medium wave channel, it could provide much better sounding audio than AM, send additional data, similar to what's available on DAB/DAB+ or have two AM-quality voice programs at the same time. The downside of this was that, like for DAB, you'd need a new receiver.
This is where the problem appears: Because there are so few receivers available, stations don't want to upgrade their equipment to new standards, and on the other hand, because there are so few broadcasters, manufacturers don't want to start making DRM receivers in large amount. So today, even if you wanted to buy a DRM receiver, it will be difficult. Of course, there's the price as well, because the DRM receivers are much more expensive than usual AM/FM receivers and even FM/DAB receivers.

On the other hand, I suspect that this expectation of technology change has also reduced acceptance of backwards-compatible upgrades to AM broadcasting. Only a few stations support the AM Signalling System, which allows transmission of station identification and other information, similar to RDS on FM. I've also not seen any receivers that can decode AMSS.

Furthermore, medium-wave AM is used for regional and intra-continental coverage, while short-wave is usually used for intercontinental coverage. Countries that need medium-wave to cover their territory usually have relatively low population density, are poor or are a combination of both. The result is that the countries that need this technological update the most, can't afford it and need to stick with old-style AM.

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    \$\begingroup\$ +1, I couldn't agree more. I, myself, am hesitant to buy new receivers (like DVB-T) because even if they're not expensive, I don't want to support trow-away-ism and I hate to waste environmental resources for something that will not be able to decode a signal less than ten years from now, not because it's broken, but because the signal gets shut down. When I climb my roof to install an antenna, I want it to be usable for a long time. Same thing when I check out a new receiver. This year, the world's resources were spent on August 8. Since then, we're creating debt we can never pay back. \$\endgroup\$ – zebonaut Sep 8 '16 at 8:55
  • \$\begingroup\$ @zebonaut In this whole transition story, I'm just happy that my country decided to skip DVB-T altogether and move directly to DVB-T2. On the other hand, we've had issues with manufacturers who were trying to force sales of DVB-T1 TVs that would never be useful! \$\endgroup\$ – AndrejaKo Sep 8 '16 at 13:19
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I live in Hong Kong and listen to am864 (and sometimes am567) all the time. All of the programming content for FM stations in HK are not good (DAB is awful). However, the content of some AM stations in HK are quite good and listen to all of the time. When I was growing up I would enjoy listening to KNX1040 from my hometown of Santa Barbara - especially the radio drama hour while camping deep in the mountains. That was on only radio station you could get sometimes. Santa Barbara could not pickup FM stations from Los Angeles easily, but received AM stations easily; especially at night. I have been an avid radio amateur all of my life and I prefer to listen to AM/SSB/CW modulated signals. AM stations are more exotic and fun to listen to because it is magical to hear something transmitted from a far away place. I do agree there is a decline in the popularity of AM, but I hope it will never go away.

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Does amplitude modulation have any huge advantages over frequency modulation that it's worth keeping the hardware alive?

In one word, simplicity. It is trivial to both "encode" and transmit AM signals, and receive and "decode" them. The AM process is well-known and low-cost, so remains a valid medium for some. And since "decoding" is so easy, even very very weak signals (from far away) can still be heard. AM also utilizes a lower carrier frequency. Lower RF frequencies tend to "bend" around obstacles more than higher frequencies would. (This is why 2.5GHz WiFi works better in some homes than 5GHz, all other things being equal.)

Modern encoding schemes (other than AM) achieve higher quality by sacrificing this simple scheme for more complex ones. Here is a nice comparison between AM and FM. The end result is that yes, FM may sound better, but it uses more complex modulation (frequency domain) and a higher carrier frequency. There are a slew of reasons why modern signal modulation types are not as robust as AM. A few of these are:

  • Higher frequencies tend to be more line-of-sight, so are more obstructed by trees, buildings, clouds, etc.
  • Higher-frequency reflections can more easily interfere with themselves, especially since they are more reflective.
  • FM has higher bandwidth than AM, so thus can carry more information, but occupies a larger RF frequency band. AM uses only one frequency (for standard AM.)
  • FM is "cleaner" than AM since the modulation is frequency-shift (which noise does not contribute as much to, on average) versus amplitude-shift (which noise does contribute to.)
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