more at http://scitech.quickfound.net "FREQUENCY MODULATION - PART I - BASIC PRINCIPLES: FUNDAMENTALS OF AM AND FM RADIO COMMUNICATION, HOW FM ELIMINATES PROBLEM OF ELECTRICAL INTERFERENCE, FUNCTIONING OF FM RADIO EXAMINED IN DETAIL." Reupload of a previously uploaded film, in one piece instead of multiple parts, and with improved video & sound. US Army Training Film TF11-3482 The 1944 film "Basic Principles of Frequency Modulation" is also excellent: https://www.youtube.com/watch?v=mu3ASt2kwFo Public domain film from the US National Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied. The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original). http://creativecommons.org/licenses/by-sa/3.0/ http://en.wikipedia.org/wiki/Frequency_modulation In telecommunications and signal processing, frequency modulation (FM) conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant. In analog applications, the difference between the instantaneous and the base frequency of the carrier is directly proportional to the instantaneous value of the input-signal amplitude. Digital data can be sent by shifting the carrier's frequency among a range of settings, a technique known as frequency-shift keying. FSK (digital FM) is widely used in data and fax modems. Morse code transmission has been sent this way, and FASK was used in early telephone-line modems. Radioteletype also uses FSK. FM modulation is also used in telemetry, radar, seismic prospecting and newborn EEG seizure monitoring. Frequency modulation is known as phase modulation when the carrier phase modulation is the time integral of the FM signal. FM is widely used for broadcasting music and speech, two-way radio systems, magnetic tape-recording systems and some video-transmission systems. In radio systems, frequency modulation with sufficient bandwidth provides an advantage in cancelling naturally-occurring noise. Radio Edwin Howard Armstrong (1890--1954) was an American electrical engineer who invented wideband frequency modulation (FM) radio. He patented the regenerative circuit in 1914, the superheterodyne receiver in 1918 and the super-regenerative circuit in 1922. Armstrong presented his paper, "A Method of Reducing Disturbances in Radio Signaling by a System of Frequency Modulation", (which first described FM radio) before the New York section of the Institute of Radio Engineers on November 6, 1935. The paper was published in 1936. As the name implies, wideband FM (WFM) requires a wider signal bandwidth than amplitude modulation by an equivalent modulating signal; this also makes the signal more robust against noise and interference. Frequency modulation is also more robust against signal-amplitude-fading phenomena. As a result, FM was chosen as the modulation standard for high frequency, high fidelity radio transmission, hence the term "FM radio" (although for many years the BBC called it "VHF radio" because commercial FM broadcasting uses part of the VHF band—the FM broadcast band). FM receivers employ a special detector for FM signals and exhibit a phenomenon known as the capture effect, in which the tuner "captures" the stronger of two stations on the same frequency while rejecting the other (compare this with a similar situation on an AM receiver, where both stations can be heard simultaneously)... An FM signal can also be used to carry a stereo signal; this is done with multiplexing and demultiplexing before and after the FM process. The FM modulation and demodulation process is identical in stereo and monaural processes. A high-efficiency radio-frequency switching amplifier can be used to transmit FM signals (and other constant-amplitude signals)... Normal (analog) TV sound is also broadcast using FM...

• published: 08 Sep 2015
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