RADIO
Radio is the transmission of signals by modulation of
electromagnetic waves with frequencies below those of visible
light. Electromagnetic radiation travels by means of oscillating
electromagnetic fields that pass through the air and the vacuum
of space. Information is carried by systematically changing
(modulating) some property of the radiated waves, such as
amplitude, frequency, or phase. When radio waves pass an
electrical conductor, the oscillating fields induce an alternating
current in the conductor. This can be detected and transformed
into sound or other signals that carry information.
Etymology
Originally, radio or radiotelegraphy was called "wireless telegraphy", which was
shortened to "wireless" by the British. The prefix radio- in the sense of wireless
transmission, was first recorded in the word radioconductor, coined by the French
physicist Édouard Branly in 1897 and based on the verb to radiate (in Latin
"radius" means "spoke of a wheel, beam of light, ray"). "Radio" as a noun is said to
have been coined by the advertising expert Waldo Warren (White 1944). This
word also appears in a 1907 article by Lee De Forest, was adopted by the United
States Navy in 1912 and became common by the time of the first commercial
broadcasts in the United States in the 1920s. (The noun "broadcasting" itself came
from an agricultural term, meaning "scattering seeds widely".) The term was then
adopted by other languages in Europe and Asia. British Commonwealth countries
continued to mainly use the term "wireless" until the mid-20th century, though the
magazine of the BBC in the UK has been called Radio Times ever since it was first
published in the early 1920s.
In recent years the term "wireless" has gained renewed popularity through the rapid
growth of short-range computer networking, e.g., Wireless Local Area Network
(WLAN), WiFi, and Bluetooth, as well as mobile telephony, e.g., GSM and
UMTS. Today, the term "radio" often refers to the actual transceiver device or
chip, whereas "wireless" refers to the system and/or method used for radio
communication, hence one talks about radio transceivers and Radio Frequency
Identification (RFID), but about wireless devices and wireless sensor network.
Processes
Radio systems used for communications will have the following elements. With
more than 100 years of development, each process is implemented by a wide range
of methods, specialized for different communications purposes.
Each system contains a transmitter. This consists of a source of electrical energy,
producing alternating current of a desired frequency of oscillation. The transmitter
contains a system to modulate (change) some property of the energy produced to
impress a signal on it. This modulation might be as simple as turning the energy on
and off, or altering more subtle properties such as amplitude, frequency, phase, or
combinations of these properties. The transmitter sends the modulated electrical
energy to a tuned resonant antenna; this structure converts the rapidly-changing
alternating current into an electromagnetic wave that can move through free space
(sometimes with a particular polarisation).
Electromagnetic waves travel through space either directly, or have their path
altered by reflection, refraction or diffraction. The intensity of the waves
diminishes due to geometric dispersion (the inverse-square law); some energy may
also be absorbed by the intervening medium in some cases. Noise will generally
alter the desired signal; this electromagnetic interference comes from natural
sources, as well as from artificial sources such as other transmitters and accidental
radiators. Noise is also produced at every step due to the inherent properties of the
devices used. If the magnitude of the noise is large enough, the desired signal will
no longer be discernible; this is the fundamental limit to the range of radio
communications.
The electromagnetic wave is intercepted by a tuned receiving antenna; this
structure captures some of the energy of the wave and returns it to the form of
oscillating electrical currents. At the receiver, these currents are demodulated,
which is conversion to a usable signal form by a detector sub-system. The receiver
is "tuned" to respond preferentially to the desired signals, and reject undesired
signals.
Early radio systems relied entirely on the energy collected by an antenna to
produce signals for the operator. Radio became more useful after the invention of
electronic devices such as the vacuum tube and later the transistor, which made it
possible to amplify weak signals. Today radio systems are used for applications
from walkie-talkie children's toys to the control of space vehicles, as well as for
broadcasting, and many other applications.
Electromagnetic spectrum
Radio frequencies occupy the range from a few tens of hertz to three hundred
gigahertz, although commercially important uses of radio use only a small part of
this spectrum. Other types of electromagnetic radiation, with frequencies above the
RF range, are microwave, infrared, visible light, ultraviolet, X-rays and gamma
rays. Since the energy of an individual photon of radio frequency is too low to
remove an electron from an atom, radio waves are classified as non-ionizing
radiation.
Invention
The meaning and usage of the word "radio" has developed in parallel with
developments within the field and can be seen to have three distinct phases:
electromagnetic waves and experimentation; wireless communication and technical
development; and radio broadcasting and commercialization. Many individuals --
inventors, engineers, developers, businessmen - contributed to produce the modern
idea of radio and thus the origins and 'invention' are multiple and controversial.
Early radio could not transmit sound or speech and was called the "wireless
telegraph".
Development from a laboratory demonstration to a commercial entity spanned
several decades and required the efforts of many practitioners. Experiments, later
patented, were undertaken by Thomas Edison and his employees of Menlo Park.
Edison applied in 1885 to the U.S. Patent Office for his patent on an electrostatic
coupling system between elevated terminals. The patent was granted as U.S. Patent
465,971 on December 29, 1891. The Marconi Company would later purchase
rights to the Edison patent to protect them legally from lawsuits. Tesla
demonstrating wireless transmissions during his high frequency and potential
lecture of 1891. After continued research, Tesla presented the fundamentals of
radio in 1893.
In 1893, in St. Louis, Missouri, Nikola Tesla made devices for his experiments
with electricity. Addressing the Franklin Institute in Philadelphia and the National
Electric Light Association, he described and demonstrated the principles of his
wireless work. The descriptions contained all the elements that were later
incorporated into radio systems before the development of the vacuum tube. He
initially experimented with magnetic receivers, unlike the coherers (detecting
devices consisting of tubes filled with iron filings which had been invented by
Temistocle Calzecchi-Onesti at Fermo in Italy in 1884) used by Guglielmo
Marconi and other early experimenters. A demonstration of wireless telegraphy
took place in the lecture theater of the Oxford University Museum of Natural
History on August 14, 1894, carried out by Professor Oliver Lodge and Alexander
Muirhead. During the demonstration a radio signal was sent from the neighboring
Clarendon laboratory building, and received by apparatus in the lecture theater.
In 1895 Alexander Stepanovich Popov built his first radio receiver, which
contained a coherer. Further refined as a lightning detector, it was presented to the
Russian Physical and Chemical Society on May 7, 1895. A depiction of Popov's
lightning detector was printed in the Journal of the Russian Physical and Chemical
Society the same year. Popov's receiver was created on the improved basis of
Lodge's receiver, and originally intended for reproduction of its experiments.
Commercialization
Telephone Herald in Budapest, Hungary (1901).
In 1896, Marconi was awarded the British patent 12039, Improvements in
transmitting electrical impulses and signals and in apparatus there-for, for radio.
In 1897 he established a radio station on the Isle of Wight, England. Marconi
opened his "wireless" factory in Hall Street, Chelmsford, England in 1898,
employing around 50 people.
The next advancement was the vacuum tube detector, invented by Westinghouse
engineers. On Christmas Eve, 1906, Reginald Fessenden used a synchronous
rotary-spark transmitter for the first radio program broadcast, from Ocean Bluff-
Brant Rock, Massachusetts. Ships at sea heard a broadcast that included Fessenden
playing O Holy Night on the violin and reading a passage from the Bible. This was,
for all intents and purposes, the first transmission of what is now known as
amplitude modulation or AM radio. The first radio news program was broadcast
August 31, 1920 by station 8MK in Detroit, Michigan, which survives today as all-
news format station WWJ under ownership of the CBS network. The first college
radio station began broadcasting on October 14, 1920, from Union College,
Schenectady, New York under the personal call letters of Wendell King, an
African-American student at the school. That month 2ADD, later renamed WRUC
in 1940, aired what is believed to be the first public entertainment broadcast in the
United States, a series of Thursday night concerts initially heard within a 100-mile
(160 km) radius and later for a 1,000-mile (1,600 km) radius. In November 1920, it
aired the first broadcast of a sporting event. At 9 pm on August 27, 1920, Sociedad
Radio Argentina aired a live performance of Richard Wagner's Parsifal opera from
the Coliseo Theater in downtown Buenos Aires. Only about twenty homes in the
city had receivers to tune in this radio program. Meanwhile, regular entertainment
broadcasts commenced in 1922 from the Marconi Research Centre at Writtle,
England.
American girl listens to radio during the Great Depression.
One of the first developments in the early 20th century (1900-1959) was that
aircraft used commercial AM radio stations for navigation. This continued until the
early 1960s when VOR systems finally became widespread (though AM stations
are still marked on U.S. aviation charts). In the early 1930s, single sideband and
frequency modulation were invented by amateur radio operators. By the end of the
decade, they were established commercial modes. Radio was used to transmit
pictures visible as television as early as the 1920s. Commercial television
transmissions started in North America and Europe in the 1940s. In 1954, the
Regency company introduced a pocket transistor radio, the TR-1, powered by a
"standard 22.5 V Battery".
In 1960, the Sony company introduced its first transistorized radio. It was small
enough to fit in a vest pocket, and able to be powered by a small battery. It was
durable, because it had no vacuum tubes to burn out. Over the next 20 years,
transistors replaced tubes almost completely except for very high-power
transmitter uses. By 1963, color television was being regularly broadcast
commercially (though not all broadcasts or programs were in color), and the first
(radio) communication satellite, Telstar, was launched. In the late 1960s, the U.S.
long-distance telephone network began to convert to a digital network, employing
digital radios for many of its links. In the 1970s, LORAN became the premier
radio navigation system. Soon, the U.S. Navy experimented with satellite
navigation, culminating in the invention and launch of the GPS constellation in
1987. In the early 1990s, amateur radio experimenters began to use personal
computers with audio cards to process radio signals. In 1994, the U.S. Army and
DARPA launched an aggressive, successful project to construct a software-defined
radio that can be programmed to be virtually any radio by changing its software
program. Digital transmissions began to be applied to broadcasting in the late
1990s.
Uses of radio
Early uses were maritime, for sending telegraphic messages using Morse code
between ships and land. The earliest users included the Japanese Navy scouting the
Russian fleet during the Battle of Tsushima in 1905. One of the most memorable
uses of marine telegraphy was during the sinking of the RMS Titanic in 1912,
including communications between operators on the sinking ship and nearby
vessels, and communications to shore stations listing the survivors.
Radio was used to pass on orders and communications between armies and navies
on both sides in World War I; Germany used radio communications for diplomatic
messages once it discovered that its submarine cables had been tapped by the
British. The United States passed on President Woodrow Wilson's Fourteen Points
to Germany via radio during the war. Broadcasting began from San Jose,
California in 1909, and became feasible in the 1920s, with the widespread
introduction of radio receivers, particularly in Europe and the United States.
Besides broadcasting, point-to-point broadcasting, including telephone messages
and relays of radio programs, became widespread in the 1920s and 1930s. Another
use of radio in the pre-war years was the development of detection and locating of
aircraft and ships by the use of radar (RAdio Detection And Ranging).
Today, radio takes many forms, including wireless networks and mobile
communications of all types, as well as radio broadcasting. Before the advent of
television, commercial radio broadcasts included not only news and music, but
dramas, comedies, variety shows, and many other forms of entertainment. Radio
was unique among methods of dramatic presentation in that it used only sound. For
more, see radio programming.
Audio
A Fisher 500 AM/FM hi-fi receiver from 1959.
AM radio uses amplitude modulation, in which the amplitude of the transmitted
signal is made proportional to the sound amplitude captured (transduced) by the
microphone, while the transmitted frequency remains unchanged. Transmissions
are affected by static and interference because lightning and other sources of radio
emissions on the same frequency add their amplitudes to the original transmitted
amplitude. In the early part of the 20th century, American AM radio stations
broadcast with powers as high as 500 kW, and some could be heard worldwide;
these stations' transmitters were commandeered for military use by the US
Government during World War II. Currently, the maximum broadcast power for a
civilian AM radio station in the United States and Canada is 50 kW, and the
majority of stations that emit signals this powerful were grandfathered in (see List
of 50kw AM radio stations in the USA). In 1986 KTNN received the last granted
50,000 watt license. These 50 kW stations are generally called "clear channel"
stations (not to be confused with Clear Channel Communications), because within
North America each of these stations has exclusive use of its broadcast frequency
throughout part or all of the broadcast day.
Bush House, home of the BBC World Service.
FM broadcast radio sends music and voice with higher fidelity than AM radio. In
frequency modulation, amplitude variation at the microphone causes the
transmitter frequency to fluctuate. Because the audio signal modulates the
frequency and not the amplitude, an FM signal is not subject to static and
interference in the same way as AM signals. Due to its need for a wider bandwidth,
FM is transmitted in the Very High Frequency (VHF, 30 MHz to 300 MHz) radio
spectrum. VHF radio waves act more like light, traveling in straight lines; hence
the reception range is generally limited to about 50-100 miles. During unusual
upper atmospheric conditions, FM signals are occasionally reflected back towards
the Earth by the ionosphere, resulting in long distance FM reception. FM receivers
are subject to the capture effect, which causes the radio to only receive the
strongest signal when multiple signals appear on the same frequency. FM receivers
are relatively immune to lightning and spark interference.
High power is useful in penetrating buildings, diffracting around hills, and
refracting in the dense atmosphere near the horizon for some distance beyond the
horizon. Consequently, 100,000 watt FM stations can regularly be heard up to 100
miles (160 km) away, and farther (e.g., 150 miles, 240 km) if there are no
competing signals. A few old, "grandfathered" stations do not conform to these
power rules. WBCT-FM (93.7) in Grand Rapids, Michigan, USA, runs 320,000
watts ERP, and can increase to 500,000 watts ERP by the terms of its original
license. Such a huge power level does not usually help to increase range as much
as one might expect, because VHF frequencies travel in nearly straight lines over
the horizon and off into space. Nevertheless, when there were fewer FM stations
competing, this station could be heard near Bloomington, Illinois, USA, almost
300 miles (500 km) away. FM subcarrier services are secondary signals
transmitted in a "piggyback" fashion along with the main program. Special
receivers are required to utilize these services. Analog channels may contain
alternative programming, such as reading services for the blind, background music
or stereo sound signals. In some extremely crowded metropolitan areas, the sub-
channel program might be an alternate foreign language radio program for various
ethnic groups. Sub-carriers can also transmit digital data, such as station
identification, the current song's name, web addresses, or stock quotes. In some
countries, FM radios automatically re-tune themselves to the same channel in a
different district by using sub-bands.
Aviation voice radios use VHF AM. AM is used so that multiple stations on the
same channel can be received. (Use of FM would result in stronger stations
blocking out reception of weaker stations due to FM's capture effect). Aircraft fly
high enough that their transmitters can be received hundreds of miles (or
kilometres) away, even though they are using VHF.
Marine voice radios can use single sideband voice (SSB) in the shortwave High
Frequency (HF—3 MHz to 30 MHz) radio spectrum for very long ranges or
narrowband FM in the VHF spectrum for much shorter ranges. Narrowband FM
sacrifices fidelity to make more channels available within the radio spectrum, by
using a smaller range of radio frequencies, usually with five kHz of deviation,
versus the 75 kHz used by commercial FM broadcasts, and 25 kHz used for TV
sound.
Government, police, fire and commercial voice services also use narrowband FM
on special frequencies. Early police radios used AM receivers to receive one-way
dispatches.
Civil and military HF (high frequency) voice services use shortwave radio to
contact ships at sea, aircraft and isolated settlements. Most use single sideband
voice (SSB), which uses less bandwidth than AM. On an AM radio SSB sounds
like ducks quacking, or the adults in a Charlie Brown cartoon. Viewed as a graph
of frequency versus power, an AM signal shows power where the frequencies of
the voice add and subtract with the main radio frequency. SSB cuts the bandwidth
in half by suppressing the carrier and (usually) lower sideband. This also makes the
transmitter about three times more powerful, because it doesn't need to transmit the
unused carrier and sideband.
TETRA, Terrestrial Trunked Radio is a digital cell phone system for military,
police and ambulances. Commercial services such as XM, WorldSpace and Sirius
offer encrypted digital Satellite radio.
Telephony
Mobile phones transmit to a local cell site (transmitter/receiver) that ultimately
connects to the public switched telephone network (PSTN) through an optic fiber
or microwave radio and other network elements. When the mobile phone nears the
edge of the cell site's radio coverage area, the central computer switches the phone
to a new cell. Cell phones originally used FM, but now most use various digital
modulation schemes. Recent developments in Sweden (such as DROPme) allow
for the instant downloading of digital material from a radio broadcast (such as a
song) to a mobile phone.
Satellite phones use satellites rather than cell towers to communicate.
Video
Television sends the picture as AM and the sound as AM or FM, with the sound
carrier a fixed frequency (4.5 MHz in the NTSC system) away from the video
carrier. Analog television also uses a vestigial sideband on the video carrier to
reduce the bandwidth required.
Digital television uses 8VSB modulation in North America (under the ATSC
digital television standard), and COFDM modulation elsewhere in the world (using
the DVB-T standard). A Reed–Solomon error correction code adds redundant
correction codes and allows reliable reception during moderate data loss. Although
many current and future codecs can be sent in the MPEG-2 transport stream
container format, as of 2006 most systems use a standard-definition format almost
identical to DVD: MPEG-2 video in Anamorphic widescreen and MPEG layer 2
(MP2) audio. High-definition television is possible simply by using a higher-
resolution picture, but H.264/AVC is being considered as a replacement video
codec in some regions for its improved compression. With the compression and
improved modulation involved, a single "channel" can contain a high-definition
program and several standard-definition programs.
Navigation
All satellite navigation systems use satellites with precision clocks. The satellite
transmits its position, and the time of the transmission. The receiver listens to four
satellites, and can figure its position as being on a line that is tangent to a spherical
shell around each satellite, determined by the time-of-flight of the radio signals
from the satellite. A computer in the receiver does the math.
Radio direction-finding is the oldest form of radio navigation. Before 1960
navigators used movable loop antennas to locate commercial AM stations near
cities. In some cases they used marine radiolocation beacons, which share a range
of frequencies just above AM radio with amateur radio operators. LORAN systems
also used time-of-flight radio signals, but from radio stations on the ground. VOR
(Very High Frequency Omnidirectional Range), systems (used by aircraft), have an
antenna array that transmits two signals simultaneously. A directional signal
rotates like a lighthouse at a fixed rate. When the directional signal is facing north,
an omnidirectional signal pulses. By measuring the difference in phase of these
two signals, an aircraft can determine its bearing or radial from the station, thus
establishing a line of position. An aircraft can get readings from two VORs and
locate its position at the intersection of the two radials, known as a "fix." When the
VOR station is collocated with DME (Distance Measuring Equipment), the aircraft
can determine its bearing and range from the station, thus providing a fix from only
one ground station. Such stations are called VOR/DMEs. The military operates a
similar system of navaids, called TACANs, which are often built into VOR
stations. Such stations are called VORTACs. Because TACANs include distance
measuring equipment, VOR/DME and VORTAC stations are identical in
navigation potential to civil aircraft.
Radar
Radar (Radio Detection And Ranging) detects objects at a distance by bouncing
radio waves off them. The delay caused by the echo measures the distance. The
direction of the beam determines the direction of the reflection. The polarization
and frequency of the return can sense the type of surface. Navigational radars scan
a wide area two to four times per minute. They use very short waves that reflect
from earth and stone. They are common on commercial ships and long-distance
commercial aircraft.
General purpose radars generally use navigational radar frequencies, but modulate
and polarize the pulse so the receiver can determine the type of surface of the
reflector. The best general-purpose radars distinguish the rain of heavy storms, as
well as land and vehicles. Some can superimpose sonar data and map data from
GPS position.
Search radars scan a wide area with pulses of short radio waves. They usually scan
the area two to four times a minute. Sometimes search radars use the Doppler
effect to separate moving vehicles from clutter. Targeting radars use the same
principle as search radar but scan a much smaller area far more often, usually
several times a second or more. Weather radars resemble search radars, but use
radio waves with circular polarization and a wavelength to reflect from water
droplets. Some weather radar use the Doppler effect to measure wind speeds.
Data (digital radio)
Most new radio systems are digital, see also: Digital TV, Satellite
Radio, Digital Audio Broadcasting. The oldest form of digital
broadcast was spark gap telegraphy, used by pioneers such as
Marconi. By pressing the key, the operator could send messages
in Morse code by energizing a rotating commutating spark gap.
The rotating commutator produced a tone in the receiver, where
a simple spark gap would produce a hiss, indistinguishable from
static. Spark gap transmitters are now illegal, because their
transmissions span several hundred megahertz. This is very
wasteful of both radio frequencies and power.
The next advance was continuous wave telegraphy, or CW (Continuous Wave), in
which a pure radio frequency, produced by a vacuum tube electronic oscillator was
switched on and off by a key. A receiver with a local oscillator would "heterodyne"
with the pure radio frequency, creating a whistle-like audio tone. CW uses less
than 100 Hz of bandwidth. CW is still used, these days primarily by amateur radio
operators (hams). Strictly, on-off keying of a carrier should be known as
"Interrupted Continuous Wave" or ICW or on-off keying (OOK).
Radio teletypes usually operate on short-wave (HF) and are much loved by the
military because they create written information without a skilled operator. They
send a bit as one of two tones. Groups of five or seven bits become a character
printed by a teletype. From about 1925 to 1975, radio teletype was how most
commercial messages were sent to less developed countries. These are still used by
the military and weather services.
Aircraft use a 1200 Baud radioteletype service over VHF to send their ID, altitude
and position, and get gate and connecting-flight data. Microwave dishes on
satellites, telephone exchanges and TV stations usually use quadrature amplitude
modulation (QAM). QAM sends data by changing both the phase and the
amplitude of the radio signal. Engineers like QAM because it packs the most bits
into a radio signal when given an exclusive (non-shared) fixed narrowband
frequency range. Usually the bits are sent in "frames" that repeat. A special bit
pattern is used to locate the beginning of a frame.
Communication systems that limit themselves to a fixed
narrowband frequency range are vulnerable to jamming. A variety
of jamming-resistant spread spectrum techniques were initially
developed for military use, most famously for Global Positioning
System satellite transmissions. Commercial use of spread
spectrum began in the 1980s. Bluetooth, most cell phones, and
the 802.11b version of Wi-Fi each use various forms of spread
spectrum.
Systems that need reliability, or that share their frequency with other services, may
use "coded orthogonal frequency-division multiplexing" or COFDM. COFDM
breaks a digital signal into as many as several hundred slower subchannels. The
digital signal is often sent as QAM on the subchannels. Modern COFDM systems
use a small computer to make and decode the signal with digital signal processing,
which is more flexible and far less expensive than older systems that implemented
separate electronic channels. COFDM resists fading and ghosting because the
narrow-channel QAM signals can be sent slowly. An adaptive system, or one that
sends error-correction codes can also resist interference, because most interference
can affect only a few of the QAM channels. COFDM is used for Wi-Fi, some cell
phones, Digital Radio Mondiale, Eureka 147, and many other local area network,
digital TV and radio standards.
Heating
Radio-frequency energy generated for heating of objects
is generally not intended to radiate outside of the
generating equipment, to prevent interference with
other radio signals. Microwave ovens use intense
radio waves to heat food. Diathermy equipment is
used in surgery for sealing of blood vessels. Induction
furnaces are used for mel
Amateur radio service
Amateur radio, also known as "ham radio", is a hobby in which
enthusiasts are licensed to communicate on a number of bands in
the radio frequency spectrum non-commercially and for their own
enjoyment. They may also provide emergency and public service
assistance. This has been very beneficial in emergencies, saving
lives in many instances. Radio amateurs use a variety of modes,
including nostalgic ones like Morse code and experimental ones
like Low-Frequency Experimental Radio. Several forms of radio
were pioneered by radio amateurs and later became
commercially important including FM, single-sideband (SSB), AM,
digital packet radio and satellite repeaters. Some amateur
frequencies may be disrupted by power-line internet service.
Unlicensed radio services
Unlicensed, government-authorized personal radio services such as Citizens'
band radio in Australia, the USA, and Europe, and Family Radio Service and
Multi-Use Radio Service in North America exist to provide simple, (usually) short
range communication for individuals and small groups, without the overhead of
licensing. Similar services exist in other parts of the world. These radio services
involve the use of handheld units.
Free radio stations, sometimes called pirate radio or "clandestine" stations, are
unauthorized, unlicensed, illegal broadcasting stations. These are often low power
transmitters operated on sporadic schedules by hobbyists, community activists, or
political and cultural dissidents. Some pirate stations operating offshore in parts of
Europe and the United Kingdom more closely resembled legal stations,
maintaining regular schedules, using high power, and selling commercial
advertising time.
Radio control (R C)
Radio remote controls use radio waves to transmit control data to a remote object
as in some early forms of guided missile, some early TV remotes and a range of
model boats, cars and airplanes. Large industrial remote-controlled equipment such
as cranes and switching locomotives now usually use digital radio techniques to
ensure safety and reliability.
In Madison Square Garden, at the Electrical Exhibition of 1898, Nikola Tesla
successfully demonstrated a radio-controlled boat. He was awarded U.S. patent
No. 613,809 for a "Method of and Apparatus for Controlling Mechanism of
Moving Vessels or Vehicles."
