Itís not news that AM broadcast radio is having a difficult time. With so many alternatives for real-time transmission of news, sports, music, and more via the Internet directly to PCs, handheld mobile devices, and cars, as well as availability of downloaded and stored playback, the need which AM fills is shrinking. Despite the upbeat statistics from the broadcasters which spin the sketchy data in the most positive way possible, the reality is that occasional and dedicated listenership has fallen, and most people seem to get their dose of AM, if any, as accidental background sound at the luncheonette.
AM is not the only broadcast medium which is struggling. The audience of its younger sibling FM is also shrinking for many of the same reasons. The drop has been less severe, since FM at least has the virtue of better quality audio due to its bandwidth and modulation technique, as well as much greater noise immunity (AM is inherently very susceptible to atmospheric and other noise sources).
The standard time-domain representation of amplitude versus frequency modulation does not show the tradeoff: FM is far more resistant to ubiquitous amplitude-induced noise sources, but at a cost of requiring more bandwidth for a given modulating signal
However, standard FM Ė which uses analog frequency modulation of a carrier Ė may also be have limited days. According to a news report, Norway will be the first county to switch off all analog FM broadcasts by 2017 and replace them with digital audio broadcasting (DAB), sometimes called digital radio and high-definition radio. Other countries are considering similar moves.
In DAB, the analog audio is digitized, compressed using an MPEG algorithm, and then modulates the carrier using coded orthogonal frequency division multiplexing (COFDM). DAB was first deployed commercially in 1995 and is in widespread use in Europe, but has no coverage in the United States and just a little in Canada (see Digital Audio Broadcasting--Wikipedia ).
The advantages of DAB are that you can pack more channels into the spectrum, a precious and limited resource. According to the article, the Norwegian authorities claim "the DAB system in Norway already offers 22 national channels, compared to just five on the FM band, and has the capacity for 20 more." In addition, the decoding algorithm used for DAB can accommodate fading and multipath, which conventional FM cannot do. The channel encoding can also provide information about what is being played (song title, artist, length, upcoming playlist) which users now expect from their music sources. Although the decoding process is more complex than analog FM, today's ICs and single-chip receivers make the difference negligible, while the benefits are substantial.
[Interestingly, key elements of both AM and FM broadcasting were developed largely by one man, Major E. H. Armstrong. After he invented the superregenerative receiver, he went on to invent the superheterodyne receiver architecture used which formed the basis for low-cost, mass-market five-tube AM radios. After that triumph, Armstrong conceived of and built the first FM transmitter and receiver (it had over 200 vacuum tubes!) to get around the inherent static and other noise susceptibility of AM. Although conventional expert wisdom said he was going the wrong way by using wideband FM, and that narrower bandwidth was the way to reduce channel input noise, he realized that you could trade off bandwidth for amplitude noise resistance, if you used a frequency-modulation scheme. ]
Are we going to miss FM radio itself? I donít think so. But as FM and AM broadcasts fade away, literally as well as figuratively, itís important to at least recognize what these two major modulation and demodulation techniques have done to spur wireless circuit design, component development, and system design (filters, for example). In fact, the modulation techniques themselves are disappearing, as they are the basis of almost all wireless and many wireless communication systems, whether analog or digital. Modulation is an analog process, even if the modulating signal is digital Ė that's physics, you can't get away from it.
What's your view on the potential disappearance of analog FM (and AM) broadcasts? Are you going to miss them, is it an "it's about time" situation, or is it a "don't care" scenario?
AM Radio: The Beat Goes On (for a Little Bit Longer)
What Does Your Noise Nemesis Look Like?