Frequency modulation

In telecommunications and signal processing, frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. This contrasts with amplitude modulation, in which the amplitude of the carrier wave varies, while the frequency remains constant.

In analog frequency modulation, such as FM radio broadcasting of an audio signal representing voice or music, the instantaneous frequency deviation, the difference between the frequency of the carrier and its center frequency, is proportional to the modulating signal.

Digital data can be encoded and transmitted via FM by shifting the carrier's frequency among a predefined set of frequencies representing digits - for example one frequency can represent a binary 1 and a second can represent binary 0. This modulation technique is known as frequency-shift keying (FSK). FSK is widely used in modems and fax modems, and can also be used to send Morse code.Radioteletype also uses FSK.

FM broadcasting

FM broadcasting is a VHF broadcasting technology, pioneered by Edwin Howard Armstrong, which uses frequency modulation (FM) to provide high-fidelity sound over broadcast radio. The term "FM band" describes the frequency band in a given country which is dedicated to FM broadcasting. This term is slightly misleading, as it equates a modulation method within a range of frequencies.

Broadcast bands

Throughout the world, the FM broadcast band falls within the VHF part of the radio spectrum. Usually 87.5 to 108.0 MHz is used, or some portion thereof, with few exceptions:

The frequency of an FM broadcast station (more strictly its assigned nominal center frequency) is usually an exact multiple of 100 kHz. In most of South Korea, the Americas, the Philippines and the Caribbean, only odd multiples are used. In some parts of Europe, Greenland and Africa, only even multiples are used. In the UK odd or even are used. In Italy, multiples of 50 kHz are used. There are other unusual and obsolete standards in some countries, including 0.001, 0.01, 0.03, 0.074, 0.5, and 0.3 MHz. However, to minimise cross-channel interference, stations operating from the same or geographically close transmitters tend to keep to at least a 0.5 MHz frequency separation even when closer spacing is technically permitted, with closer tunings reserved for more distantly spaced transmitters as potentially interfering signals are already more attenuated and so have less effect on neighbouring frequencies. RCA stereo models use multiples of 0.2 MHz, starting at 87.50 and ending at 107.90.

United States Army

The United States Army (USA) is the largest branch of the United States Armed Forces and performs land-based military operations. It is one of the seven uniformed services of the United States, and is designated as the Army of the United States in the United States Constitution, Article 2, Section 2, Clause 1 and United States Code, Title 10, Subtitle B, Chapter 301, Section 3001. As the largest and senior branch of the U.S. military, the modern U.S. Army has its roots in the Continental Army, which was formed (14 June 1775) to fight the American Revolutionary War (1775–83)—before the U.S. was established as a country. After the Revolutionary War, the Congress of the Confederation created the United States Army on 3 June 1784, to replace the disbanded Continental Army. The United States Army considers itself descended from the Continental Army, and dates its institutional inception from the origin of that armed force in 1775.

Frequency

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency. The period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example, if a newborn baby's heart beats at a frequency of 120 times a minute, its period – the interval between beats – is half a second (60 seconds (i.e., a minute) divided by 120 beats). Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio (sound) signals, radio waves, and light.

Definitions

For cyclical processes, such as rotation, oscillations, or waves, frequency is defined as a number of cycles per unit time. In physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by the Greek letter or ν (nu) (see e.g. Planck's formula). The period, usually denoted by T, is the duration of one cycle, and is the reciprocal of the frequency f:

Kent Smith

Kent Smith (March 19, 1907 – April 23, 1985) was an American actor who had a lengthy career in film, theater, and television.

Biography and acting career

Born Frank Kent Smith in New York, New York, Smith made his acting debut on Broadway in 1932 in Men Must Fight and, after spending a few years there, moved to Hollywood, California, where he made his film debut in The Garden Murder Case.

His biggest successes occurred during the 1940s in films such as Cat People (1942), Hitler's Children (1943), This Land Is Mine (1943), Three Russian Girls (1943), Youth Runs Wild (1944), The Curse of the Cat People (1944), The Spiral Staircase (1946), Nora Prentiss (1947), Magic Town (1947), My Foolish Heart (1949), The Fountainhead (1949), and The Damned Don't Cry! (1950). He continued acting in films such as Comanche (1956), Sayonara (1957), Party Girl (1958), The Mugger (1958), Imitation General (1958), The Badlanders (1958), This Earth Is Mine (1959), Strangers When We Meet (1960), Susan Slade (1961), The Balcony (1963), A Distant Trumpet (1964), Youngblood Hawke (1964), The Young Lovers (1964), The Trouble with Angels (1966), A Covenant with Death (1967), Games (1967), The Money Jungle (1968), Kona Coast (1968), Assignment to Kill (1968), Death of a Gunfighter (1969), The Games (1970), Pete 'n' Tillie (1972), Die Sister, Die! (1972), Lost Horizon (1973) and Billy Jack Goes to Washington (1977).