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radio-feature issue on mobile-phones . . . |
*Jojo*
Joined: Oct 15, 2003
Posts: > 500
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I am WONDERING (as I've been ALWAYS . . .) why there's NO - AM (amplitude modulation) in ALL  fone models which have RADIO-feature on it (and in all other brands of mobile phones too . . .), only - FM (frequency modulation) . . . 
AM (Amplitude Modulation) :
Amplitude modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent. For example, changes in the signal strength can be used to reflect the sounds to be reproduced by a speaker, or to specify the light intensity of television pixels. (Contrast this with frequency modulation, also commonly used for sound transmissions, in which the frequency is varied; and phase modulation, often used in remote controls, in which the phase is varied.)
In the mid-1870s, a form of amplitude modulation—initially called "undulatory currents"—was the first method to successfully produce quality audio over telephone lines. Beginning with Reginald Fessenden's audio demonstrations in 1906, it was also the original method used for audio radio transmissions, and remains in use today by many forms of communication—"AM" is often used to refer to the mediumwave broadcast band (see AM radio).
FM (Frequency Modulation) :
In telecommunications, frequency modulation (FM) conveys information over a carrier wave by varying its frequency (contrast this with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant). In analog applications, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. Digital data can be sent by shifting the carrier's frequency among a set of discrete values, a technique known as frequency-shift keying.
FM is commonly used at VHF radio frequencies for high-fidelity broadcasts of music and speech (see FM broadcasting). Normal (analog) TV sound is also broadcast using FM. A narrowband form is used for voice communications in commercial and amateur radio settings. The type of FM used in broadcast is generally called wide-FM, or W-FM. In two-way radio, narrowband narrow-fm (N-FM) is used to conserve bandwidth. In addition, it is used to send signals into space.
FM is also used at intermediate frequencies by most analog VCR systems, including VHS, to record the luminance (black and white) portion of the video signal. FM is the only feasible method of recording video to and retrieving video from magnetic tape without extreme distortion, as video signals have a very large range of frequency components — from a few hertz to several megahertz, too wide for equalisers to work with due to electronic noise below -60 dB. FM also keeps the tape at saturation level, and therefore acts as a form of audio noise reduction, and a simple limiter can mask variations in the playback output, and the FM capture effect removes print-through and pre-echo. A continuous pilot-tone, if added to the signal — as was done on V2000 and many Hi-band formats — can keep mechanical jitter under control and assist timebase correction.
FM is also used at audio frequencies to synthesize sound. This technique, known as FM synthesis, was popularized by early digital synthesizers and became a standard feature for several generations of personal computer sound cards.
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jcwhite_uk
Joined: Feb 18, 2004
Posts: > 500
From: Dorset, UK Phone:Xperia Z1
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There are 2 reasons why phones only use FM.
1. There are getting less and less AM radio stations.
2. The aerial required for AM reception is a largish ferrite rod that is really not ideal in a phone as it would make it a lot larger.
Checkout my photos at My Website"Duct tape is like the force. It has a light side, a dark side, and it holds the world together." |
*Jojo*
Joined: Oct 15, 2003
Posts: > 500
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@jc - OK, thanks for the INFO mate . . . 
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sadeghi85
Joined: Oct 13, 2007
Posts: 341
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Nice tutorials about communications, if anyone interested:
complextoreal.com
AM
FM |
*Jojo*
Joined: Oct 15, 2003
Posts: > 500
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@sade - Thanks for the LINKS . . .
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sadeghi85
Joined: Oct 13, 2007
Posts: 341
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On 2008-01-12 00:31:55, jcwhite_uk wrote:
1. There are getting less and less AM radio stations.
reason:
Limitations of AM radio |
*Jojo*
Joined: Oct 15, 2003
Posts: > 500
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. . . but at my END, I guess we just have the SAME (if NOT almost) AM radio stations with that of the - FM
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Access the forum with a mobile phone via esato.mobi
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Posted: 2008-01-12 00:28
