Radio masts and towers
Radio masts and towers are tall structures designed to support antennas for telecommunications and broadcasting, including television. There are two main types: self-supporting structures, they are among the tallest human-made structures. Masts are named after the broadcasting organizations that built them or use them. In the case of a mast radiator or radiating tower, the whole mast or tower is itself the transmitting antenna; the terms "mast" and "tower" are used interchangeably. However, in structural engineering terms, a tower is a self-supporting or cantilevered structure, while a mast is held up by stays or guys. Broadcast engineers in the UK use the same terminology. A mast is a ground-based or rooftop structure that supports antennas at a height where they can satisfactorily send or receive radio waves. Typical masts are of tubular steel construction. Masts themselves play no part in the transmission of mobile telecommunications. Masts tend to be cheaper to build but require an extended area surrounding them to accommodate the guy wires.
Towers are more used in cities where land is in short supply. There are a few borderline designs that are free-standing and guyed, called additionally guyed towers. For example: The Gerbrandy tower consists of a self-supporting tower with a guyed mast on top; the few remaining Blaw-Knox towers do the opposite: they have a guyed lower section surmounted by a freestanding part. Zendstation Smilde, a tall tower with a guyed mast on top with guys which go to ground. Torre de Collserola, a guyed tower with a guyed mast on top where the tower portion is not free-standing. Experimental radio broadcasting began in 1905, commercial radio broke through in the 1920s; until August 8, 1991, the Warsaw radio mast was the world's tallest supported structure on land. There are over 50 radio structures in the United States that are taller; the steel lattice is the most widespread form of construction. It provides great strength, low weight and wind resistance, economy in the use of materials. Lattices of triangular cross-section are most common, square lattices are widely used.
Guyed masts are used. When built as a tower, the structure may be taper over part or all of its height; when constructed of several sections which taper exponentially with height, in the manner of the Eiffel Tower, the tower is said to be an Eiffelized one. The Crystal Palace tower in London is an example. Guyed masts are sometimes constructed out of steel tubes; this construction type has the advantage that cables and other components can be protected from weather inside the tube and the structure may look cleaner. These masts are used for FM-/TV-broadcasting, but sometimes as mast radiator; the big mast of Mühlacker transmitting station is a good example of this. A disadvantage of this mast type is that it is much more affected by winds than masts with open bodies. Several tubular guyed masts have collapsed. In the UK, the Emley Moor and Waltham TV stations masts collapsed in the 1960s. In Germany the Bielstein transmitter collapsed in 1985. Tubular masts were not built in all countries. In Germany, France, UK, Czech Republic, Slovakia and the Soviet Union, many tubular guyed masts were built, while there are nearly none in Poland or North America.
In several cities in Russia and Ukraine several tubular guyed masts with crossbars running from the mast structure to the guys were built in the 1960s. All these masts, which are designed as 30107 KM, are used for FM and TV transmission and, except for the mast in Vinnytsia, are between 150–200-metre tall; the crossbars of these masts are equipped with a gangway that holds smaller antennas, though their main purpose is oscillation damping. Reinforced concrete towers are expensive to build but provide a high degree of mechanical rigidity in strong winds; this can be important when antennas with narrow beamwidths are used, such as those used for microwave point-to-point links, when the structure is to be occupied by people. In the 1950s, AT&T built numerous concrete towers, more resembling silos than towers, for its first transcontinental microwave route. In Germany and the Netherlands most towers constructed for point-to-point microwave links are built of reinforced concrete, while in the UK most are lattice towers.
Concrete towers can form prestigious landmarks, such as the CN Tower in Canada. In addition to accommodating technical staff, these buildings may have public areas such as observation decks or restaurants; the Stuttgart TV tower was the first tower in the world to be built in reinforced concrete. It was designed in 1956 by the local civil engineer Fritz Leonhardt. Fiberglass poles are used for low-power non-directional beacons or medium-wave broadcast transmitters. Carbon fibre monopoles and towers have traditionally been too expensive but recent developments in the way the carbon fibre tow is spun have resulted in solutions that offer strengths similar or exceeding steel for a fraction of the weight which has allowed monopoles and towers to be built in locations that were too expensive or difficult to access with the heavy lifting equipment, needed for a steel structure. Wood has been superseded in use by metal and composites for tower construction. Many wood towers were built in the UK during World War II because of a shortage of steel.
In Germany before World War II wooden towers were used at nearly all medium-wave transmission sites which hav
Fiberglass or fibreglass is a common type of fiber-reinforced plastic using glass fiber. The fibers may be flattened into a sheet, or woven into a fabric; the plastic matrix may be a thermoset polymer matrix—most based on thermosetting polymers such as epoxy, polyester resin, or vinylester—or a thermoplastic. Cheaper and more flexible than carbon fiber, it is stronger than many metals by weight, can be molded into complex shapes. Applications include aircraft, automobiles, bath tubs and enclosures, swimming pools, hot tubs, septic tanks, water tanks, pipes, orthopedic casts and external door skins. GRP covers are widely used in the water-treatment industry to help control odors. Other common names for fiberglass are glass-reinforced plastic, glass-fiber reinforced plastic or GFK; because glass fiber itself is sometimes referred to as "fiberglass", the composite is called "fiberglass reinforced plastic". This article will adopt the convention that "fiberglass" refers to the complete glass fiber reinforced composite material, rather than only to the glass fiber within it.
Glass fibers have been produced for centuries, but the earliest patent was awarded to the Prussian inventor Hermann Hammesfahr in the U. S. in 1880. Mass production of glass strands was accidentally discovered in 1932 when Games Slayter, a researcher at Owens-Illinois, directed a jet of compressed air at a stream of molten glass and produced fibers. A patent for this method of producing glass wool was first applied for in 1933. Owens joined with the Corning company in 1935 and the method was adapted by Owens Corning to produce its patented "Fiberglas" in 1936. Fiberglas was a glass wool with fibers entrapping a great deal of gas, making it useful as an insulator at high temperatures. A suitable resin for combining the fiberglass with a plastic to produce a composite material was developed in 1936 by du Pont; the first ancestor of modern polyester resins is Cyanamid's resin of 1942. Peroxide curing systems were used by then. With the combination of fiberglass and resin the gas content of the material was replaced by plastic.
This reduced the insulation properties to values typical of the plastic, but now for the first time the composite showed great strength and promise as a structural and building material. Confusingly, many glass fiber composites continued to be called "fiberglass" and the name was used for the low-density glass wool product containing gas instead of plastic. Ray Greene of Owens Corning is credited with producing the first composite boat in 1937, but did not proceed further at the time due to the brittle nature of the plastic used. In 1939 Russia was reported to have constructed a passenger boat of plastic materials, the United States a fuselage and wings of an aircraft; the first car to have a fiber-glass body was a 1946 prototype of the Stout Scarab, but the model did not enter production. Unlike glass fibers used for insulation, for the final structure to be strong, the fiber's surfaces must be entirely free of defects, as this permits the fibers to reach gigapascal tensile strengths. If a bulk piece of glass were defect-free, it would be as strong as glass fibers.
The process of manufacturing fiberglass is called pultrusion. The manufacturing process for glass fibers suitable for reinforcement uses large furnaces to melt the silica sand, kaolin clay, colemanite and other minerals until a liquid forms, it is extruded through bushings, which are bundles of small orifices. These filaments are sized with a chemical solution; the individual filaments are now bundled in large numbers to provide a roving. The diameter of the filaments, the number of filaments in the roving, determine its weight expressed in one of two measurement systems: yield, or yards per pound. Examples of standard yields are 450yield, 675yield. Tex, or grams per km. Examples of standard tex are 1100tex, 2200tex; these rovings are either used directly in a composite application such as pultrusion, filament winding, gun roving, or in an intermediary step, to manufacture fabrics such as chopped strand mat, woven fabrics, knit fabrics or uni-directional fabrics. Chopped strand mat or CSM is a form of reinforcement used in fiberglass.
It consists of glass fibers held together by a binder. It is processed using the hand lay-up technique, where sheets of material are placed on a mold and brushed with resin; because the binder dissolves in resin, the material conforms to different shapes when wetted out. After the resin cures, the hardened product finished. Using chopped strand mat gives a fiberglass with isotropic in-plane material properties. A coating or primer is applied to the roving to: help protect the glass filaments for processing and manipulation. Ensure proper bonding to the resin matrix, thus allowing for transfer of shear loads from the glass fiber
Lattice masts, or cage masts, are a type of observation mast common on major warships in the early 20th century. They are a type of hyperboloid structure, whose weight-saving design was invented by the Russian engineer Vladimir Shukhov, they were used most prominently on American dreadnought battleships and armored cruisers of the World War I era. In the age of sail masts were required to support the sails, lookouts were posted on them; the purpose of the lattice structure was to make the posts less vulnerable to shells from enemy ships, to better absorb the shock caused by firing heavy guns, isolating the delicate fire control equipment mounted on the mast tops. However, the masts were found to be damaged by the inclement weather experienced at sea by naval ships during typhoons and hurricanes: the USS Michigan's mast was bent right down to the deck by such a storm in 1918; as the caliber and range of ships' guns increased, heavier rangefinders were required, the powerful guns and engines created shock and vibrations.
The South Carolina-class battleships were the first class of American battleships to feature lattice masts, which were to become a standard fixture on all American battleships, many cruiser classes. Older vessels, including the first modern American battleship, were modernized with lattice masts during the period. In January 1918, the lattice mast of the battleship USS Michigan collapsed in a severe storm; the incident spurred an investigation by the Bureau of Construction and Repair, which found that the collapse was in part due to the fact that the mast had been lengthened, with a new section spliced in where the mast broke. In addition, fragments from a recent explosion in one of the ship's 12-inch guns had damaged the mast, the damage had not been adequately repaired; the investigation found that the mast aboard the battleship Connecticut showed signs of buckling. Throughout the 1920s and 1930s, the Navy found evidence of structural problems in the masts, in large part due to the corrosive effects of funnel gases.
At the same time as the Michigan incident, US Navy officers were gaining experience with British tripod masts for the first time while serving with the Grand Fleet during World War I. Unlike lattice masts, the heavier tripods did not suffer from vibration when steaming at high speed, they were not as susceptible to shock from gunfire, which caused the lattice masts to whip from the concussion. All American battleships, up to the Colorado-class battleships were equipped with lattice masts, although in the 1920s to 1930s, the older battleships had their lattice masts replaced with more modern tripod masts, concomitant with the addition of larger, much heavier fire-control director tops; the newer Tennessee and Colorado classes retained their original lattice masts, of heavier construction than those on earlier ships, at the start of World War II. Only four battleships were completed with lattice masts for other navies; the two Andrei Pervozvanny-class battleships of the Imperial Russian Navy had lattice masts until they were replaced with conventional masts in the beginning of the First World War.
The two United States-built Rivadavia-class battleships of the Argentine Navy, ARA Rivadavia and ARA Moreno, had lattice masts. They were the only dreadnought-type battleships built for export by the USA. Two other battleships, the US pre-dreadnoughts Mississippi and Idaho were sold to Greece in 1914; some navies considered lattice masts for their ships. Following their experience with the Andrei Pervozvannys, the Russians designed the four Gangut-class battleships with lattice masts, but constructed with pole ones; the German Imperial Navy designed its first battlecruiser, SMS Von der Tann, with lattice masts, but she was instead completed with pole masts. A lattice fire-control mast was installed on Fort Drum, a fort built by the United States to guard the entrance of Manila Bay; the mast directed the fire of the fort's 14-inch main batteries. Friedman, Norman. U. S. Battleships: An Illustrated Design History. Annapolis, Maryland: Naval Institute Press. ISBN 978-0-87021-715-9. OCLC 12214729. Hore, Peter.
Battleships of World War I. London: Southwater Books. ISBN 978-1-84476-377-1. Morison, S. L.. The American Battleship. Zenith. ISBN 0-7603-0989-2. Hythe, Thomas A. ed.. The Naval Annual.. Portsmouth: J. Griffin & Co. Melnikov, R. M.. Lineyny korabl "Andrey Pervozvanny". Saint Petersburg: Korabli i srazheniya.. McGovern, Terrance C.. American Defenses of Corregidor and Manila Bay 1898-1945. Osprey. ISBN 1-84176-427-2. Staff, Gary. German Battlecruisers: 1914–1918. Oxford: Osprey Books. ISBN 978-1-84603-009-3
Mühlacker radio transmitter
The Mühlacker Broadcasting Transmission Facility is a radio transmission facility near Mühlacker, first put into service on November 21, 1930. It uses two guyed steel tube masts as aerials and one guyed steel framework mast, which are insulated against ground, it has two transmission aerials for shortwave and one free standing steel framework tower for directional radio services. The shortwave transmitter was shut off on October 19, 2004. At time of inauguration in 1930 the transmitter, which had a power of 60 kW, used a T-type antenna spun between two 100 m high wooden lattice towers placed 310 m apart; as this antenna produced large amounts of skywave, the area of undistorted fading-free reception - was in spite of its high transmission power - at night not as large as planned and so it was planned to replace this antenna by an aerial with better skywave suppression. So in 1933-34, a 190 m high wooden tower - the tallest structure built of wood - was built, in which a vertical wire antenna, electrically enlengthened by a metal ring with 10.6 metres diameters on the top of the tower, was hung up.
At this time transmission power was increased from 60 kW to 100 kW. After inauguration of this antenna, the two original wooden towers were dismantled. One of them was rebuilt at the other at Frankfurt-Heiligenstock. In 1939/1940 a second 100 kW transmitter was installed, it used as antenna a system of 3 T-antennas, which were mounted on 3 50 metres tall guyed masts arranged in a triangle. In opposite to the first transmitter, it was including its aerial designed for a quick change of broadcasting frequency, done in case of air attacks in order to form a single frequency network with other transmitters, which hindered hostile aircraft using the signals for navigation purpose. On April 6, 1945, the wooden tower and the masts carrying the system of T-antennas were blown up by the SS to prevent its capture by the Allies in World War II. Today, the most important aerial mast in Mühlacker is a 273 m high guyed steel tube mast with a diameter of 1.67 m, located at 48°56′31″N 8°51′14″E. This mast, built in 1950, is used as a transmitter for the mediumwave frequency 576 kHz and is therefore insulated against ground.
It is is therefore double-feedable and insulated. The mast is topped with a butterfly aerial for FM-broadcasting transmitters, it is remarkable that there are flight safety lamps near the ground end of the guy ropes, to make the span of the guy ropes more visible. Two other radio masts, with heights of 130 m and 80 m, are located at the Mühlacker site; the 130 m high mast, situated at 48°56′36″N 8°51′21″E, is a steel tube mast, insulated against ground. Before 1996, it was used as a director during a spare during daytime. Transmission power was reduced to 100 kW in 1996 and the mast is now obsolete and used only as a spare aerial; the 80 m high radio mast, located at 48°56′29″N 8°51′10″E, is an insulated guyed steel framework mast with a triangular cross section. It was built in 1977, it is now used to carry aerials for mobile phone services. The three masts are arranged in a nearly straight line on the site. A T-type aerial for shortwave transmission is fixed between two small guyed steel framework masts, but was shut down on October 19, 2004.
In 1948, a 110 m tall guyed steel framework mast was built on the site at 48°56′33″N 8°51′2″E This served as a transmission aerial for the American Forces Network until 1963. From 1963 until its demolition in November 1993, the mast was used as part of a directional aerial for a mediumwave transmitter, it served as a spare FM transmitter with a butterfly aerial installed on top. The mast was demolished because it was deemed no longer necessary. Plans for a new mast have not been realized. Located here at 48°56′30″N 8°51′5″E was a 50 m steel framework mast insulated against ground, it was part of the directional aerial for the AFN transmitter described above. After 1963, it was only used as an aerial for the internal mobile radio service of the transmission facility, it was demolished in April, 2004 and replaced in the summer of 2004 with a 93 m high freestanding steel framework tower carrying aerials for directional services. List of masts List of towers Mühlacker Transmission Tower at Structurae Mühlacker AFN Radio Mast at Structurae Sendemast Mühlacker at Structurae Mühlacker Short-wave Transmitters at Structurae Ausblendmast Mühlacker at Structurae Reflektormast Mühlacker at Structurae Mühlacker Directional Radio Transmittor at Structurae http://www.magischesauge.de/muehlacker_chronik.htm http://www.skyscraperpage.com/diagrams/?b40728 http://www.skyscraperpage.com/cities/?buildingID=40731 http://www.skyscraperpage.com/diagrams/?b28031 http://www.skyscraperpage.com/diagrams/?b62537 http://www.skyscraperpage.com/diagrams/?b40733 http://www.skyscraperpage.com/diagrams/?b47129 Satellite Picture
Low frequency or LF is the ITU designation for radio frequencies in the range of 30 kilohertz to 300 kHz. As its wavelengths range from ten kilometres to one kilometre it is known as the kilometre band or kilometre wave. LF radio waves exhibit low signal attenuation, making them suitable for long-distance communications. In Europe and areas of Northern Africa and Asia, part of the LF spectrum is used for AM broadcasting as the "longwave" band. In the western hemisphere, its main use is for aircraft beacon, navigation and weather systems. A number of time signal broadcasts are broadcast in this band; because of their long wavelength, low frequency radio waves can diffract over obstacles like mountain ranges and travel beyond the horizon, following the contour of the Earth. This mode of propagation, called ground wave, is the main mode in the LF band. Ground waves must be vertically polarized, so vertical monopole antennas are used for transmitting; the attenuation of signal strength with distance by absorption in the ground is lower than at higher frequencies.
Low frequency ground waves can be received up to 2,000 kilometres from the transmitting antenna. Low frequency waves can occasionally travel long distances by reflecting from the ionosphere, although this method, called skywave or "skip" propagation, is not as common as at higher frequencies. Reflection occurs at F layers. Skywave signals can be detected at distances exceeding 300 kilometres from the transmitting antenna. In Europe and Japan, many low-cost consumer devices have since the late 1980s contained radio clocks with an LF receiver for these signals. Since these frequencies propagate by ground wave only, the precision of time signals is not affected by varying propagation paths between the transmitter, the ionosphere, the receiver. In the United States, such devices became feasible for the mass market only after the output power of WWVB was increased in 1997 and 1999. Radio signals below 50 kHz are capable of penetrating ocean depths to 200 metres, the longer the wavelength, the deeper.
The British, Indian, Swedish, United States and other navies communicate with submarines on these frequencies. In addition, Royal Navy nuclear submarines carrying ballistic missiles are under standing orders to monitor the BBC Radio 4 transmission on 198 kHz in waters near the UK, it is rumoured that they are to construe a sudden halt in transmission of the morning news programme Today, as an indicator that the UK is under attack, whereafter their sealed orders take effect. In the US, the Ground Wave Emergency Network or GWEN operated between 150 and 175 kHz, until replaced by satellite communications systems in 1999. GWEN was a land based military radio communications system which could survive and continue to operate in the case of a nuclear attack; the 2007 World Radiocommunication Conference made this band a worldwide amateur radio allocation. An international 2.1 kHz allocation, the 2200 meter band, is available to amateur radio operators in several countries in Europe, New Zealand and French overseas dependencies.
The world record distance for a two-way contact is over 10,000 km from near Vladivostok to New Zealand. As well as conventional Morse code many operators use slow computer-controlled Morse code or specialized digital communications modes; the UK allocated a 2.8 kHz sliver of spectrum from 71.6 kHz to 74.4 kHz beginning in April 1996 to UK amateurs who applied for a Notice of Variation to use the band on a noninterference basis with a maximum output power of 1 Watt ERP. This was withdrawn on 30 June 2003 after a number of extensions in favor of the European-harmonized 136 kHz band. Slow Morse Code from G3AQC in the UK was received 3,275 miles away, across the Atlantic Ocean, by W1TAG in the US on 21-22 November 2001 on 72.401 kHz. In the United States, there is a exemption within FCC Part 15 regulations permitting unlicensed transmissions in the frequency range of 160 to 190 kHz. Longwave radio hobbyists refer to this as the' LowFER' band, experimenters, their transmitters are called'LowFERs'.
This frequency range between 160 kHz and 190 kHz is referred to as the 1750 Meter band. Requirements from 47CFR15.217 and 47CFR15.206 include: The total input power to the final radio frequency stage shall not exceed one watt. The total length of the transmission line and ground lead shall not exceed 15 meters. All emissions below 160 kHz or above 190 kHz shall be attenuated at least 20 dB below the level of the unmodulated carrier; as an alternative to these requirements, a field strength of 2400/F microvolts/meter may be used. In all cases, operation may not cause harmful interference to licensed services. Many experimenters in this band are amateur radio operators. A regular service transmitting RTTY marine meteorological information in SYNOP code on LF is the German Meteorological Service; the DWD operates station DDH47 on 147.3 kHz using standard ITA-2 alphabet with a transmission speed of 50 baud and FSK modulation with 85 Hz shift. In parts of the world where there is no longwave broadcasting service, Non-directional beacons used for aeronavigation operate on 190–300 kHz.
In Europe and Africa, the NDB allocation starts on 283.5 kHz. The LORAN-C radio navigation system operated on 100 kHz. In the past, the Decca Navigator System operated betw
In electronics and telecommunications, a transmitter or radio transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, applied to the antenna; when excited by this alternating current, the antenna radiates radio waves. Transmitters are necessary component parts of all electronic devices that communicate by radio, such as radio and television broadcasting stations, cell phones, walkie-talkies, wireless computer networks, Bluetooth enabled devices, garage door openers, two-way radios in aircraft, spacecraft, radar sets and navigational beacons; the term transmitter is limited to equipment that generates radio waves for communication purposes. Generators of radio waves for heating or industrial purposes, such as microwave ovens or diathermy equipment, are not called transmitters though they have similar circuits; the term is popularly used more to refer to a broadcast transmitter, a transmitter used in broadcasting, as in FM radio transmitter or television transmitter.
This usage includes both the transmitter proper, the antenna, the building it is housed in. A transmitter can be a separate piece of electronic equipment, or an electrical circuit within another electronic device. A transmitter and a receiver combined in one unit is called a transceiver; the term transmitter is abbreviated "XMTR" or "TX" in technical documents. The purpose of most transmitters is radio communication of information over a distance; the information is provided to the transmitter in the form of an electronic signal, such as an audio signal from a microphone, a video signal from a video camera, or in wireless networking devices, a digital signal from a computer. The transmitter combines the information signal to be carried with the radio frequency signal which generates the radio waves, called the carrier signal; this process is called modulation. The information can be added to the carrier in several different ways, in different types of transmitters. In an amplitude modulation transmitter, the information is added to the radio signal by varying its amplitude.
In a frequency modulation transmitter, it is added by varying the radio signal's frequency slightly. Many other types of modulation are used; the radio signal from the transmitter is applied to the antenna, which radiates the energy as radio waves. The antenna may be enclosed inside the case or attached to the outside of the transmitter, as in portable devices such as cell phones, walkie-talkies, garage door openers. In more powerful transmitters, the antenna may be located on top of a building or on a separate tower, connected to the transmitter by a feed line, a transmission line. Electromagnetic waves are radiated by electric charges undergoing acceleration. Radio waves, electromagnetic waves of radio frequency, are generated by time-varying electric currents, consisting of electrons flowing through a metal conductor called an antenna which are changing their velocity or direction and thus accelerating. An alternating current flowing back and forth in an antenna will create an oscillating magnetic field around the conductor.
The alternating voltage will charge the ends of the conductor alternately positive and negative, creating an oscillating electric field around the conductor. If the frequency of the oscillations is high enough, in the radio frequency range above about 20 kHz, the oscillating coupled electric and magnetic fields will radiate away from the antenna into space as an electromagnetic wave, a radio wave. A radio transmitter is an electronic circuit which transforms electric power from a power source into a radio frequency alternating current to apply to the antenna, the antenna radiates the energy from this current as radio waves; the transmitter impresses information such as an audio or video signal onto the radio frequency current to be carried by the radio waves. When they strike the antenna of a radio receiver, the waves excite similar radio frequency currents in it; the radio receiver extracts the information from the received waves. A practical radio transmitter consists of these parts: A power supply circuit to transform the input electrical power to the higher voltages needed to produce the required power output.
An electronic oscillator circuit to generate the radio frequency signal. This generates a sine wave of constant amplitude called the carrier wave, because it serves to "carry" the information through space. In most modern transmitters, this is a crystal oscillator in which the frequency is controlled by the vibrations of a quartz crystal; the frequency of the carrier wave is considered the frequency of the transmitter. A modulator circuit to add the information to be transmitted to the carrier wave produced by the oscillator; this is done by varying some aspect of the carrier wave. The information is provided to the transmitter either in the form of an audio signal, which represents sound, a video signal which represents moving images, or for data in the form of a binary digital signal which represents a sequence of bits, a bitstream. Different types of transmitters use different modulation methods to transmit information: In an AM transmitter the amplitude of the carrier wave is varied in proportion to the modulation signal.
In an FM transmitter the frequency of the carrier is varied by the modulation signal. In an FSK transmitter, which transmits digital data, the frequency of the carrier is shifted between two frequencies which represent the two binary digits, 0 and 1. Many oth