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Continuous wave modulation (Amplitude, Frequency & Phase Modulation) [HD]
Continuous wave modulation (Amplitude, Frequency & Phase Modulation) [HD]
Published: 2017/04/16
Channel: Engineering Made Easy
K1OIK presents CW for the beginning ham
K1OIK presents CW for the beginning ham
Published: 2012/10/03
Channel: burt2481
Continuous Wave technique
Continuous Wave technique
Published: 2013/04/23
Channel: Dentsply Sirona Endodontics US, CA
10 - Hours Ocean Waves crashing onto the shore Ambient Sounds for meditation relaxation Sleep Sounds
10 - Hours Ocean Waves crashing onto the shore Ambient Sounds for meditation relaxation Sleep Sounds
Published: 2012/11/02
Channel: austinstrunk
Continuous Waves Of Galactic Energy/Perseus
Continuous Waves Of Galactic Energy/Perseus
Published: 2017/05/20
Channel: BPEarthWatch
Continuous Wave technique | Dentsply Sirona
Continuous Wave technique | Dentsply Sirona
Published: 2016/02/17
Channel: Dentsply Sirona USA
Security: Continuous Wave of Condensation
Security: Continuous Wave of Condensation
Published: 2016/08/22
Channel: Dental Engineering Laboratories
Continuous-wave Doppler
Continuous-wave Doppler
Published: 2016/02/01
Channel: Echocardiography step by step
Continuous wave
Continuous wave
Published: 2015/12/30
Channel: Audiopedia
Calming Seas #1 - 11 Hours Ocean Waves Sounds Nature Relaxation Yoga Meditation Reading Sleep Study
Calming Seas #1 - 11 Hours Ocean Waves Sounds Nature Relaxation Yoga Meditation Reading Sleep Study
Published: 2013/08/07
Channel: Relaxing Music & Yoga
Continuous Wave Of Condensation Elements Obturation System
Continuous Wave Of Condensation Elements Obturation System
Published: 2013/05/07
Channel: Gary Glassman
continous wave condensation Buchanan tehnique
continous wave condensation Buchanan tehnique
Published: 2008/11/07
Channel: Sergiu Nicola
Infrared Spectroscopy: Comparing Continuous Wave (CW) and Fourier Transform (FT) - part 2 of  6
Infrared Spectroscopy: Comparing Continuous Wave (CW) and Fourier Transform (FT) - part 2 of 6
Published: 2012/10/02
Channel: owen priest
Continous Wave Obturation Technique  (Dr.Vinod Kumar, Bangalore)
Continous Wave Obturation Technique (Dr.Vinod Kumar, Bangalore)
Published: 2013/09/02
Channel: Dr.Vinod Kumar
Elements Obturation Unit - Continuous Wave Obturation
Elements Obturation Unit - Continuous Wave Obturation
Published: 2013/03/01
Channel: AxisSybronEndo
lecture 16 - Continuous Wave Lasers
lecture 16 - Continuous Wave Lasers
Published: 2017/02/20
Channel: Quantum Computing
FMCW Radar
FMCW Radar
Published: 2015/03/20
Channel: Djremorse
Continuous wave radar explanation. 4
Continuous wave radar explanation. 4
Published: 2017/01/16
Channel: harsha mangipudi
Continuous Wave Condensation
Continuous Wave Condensation
Published: 2011/05/24
Channel: Svedent
Ultrasound Physics Scanning Modes Pulsed Wave Doppler
Ultrasound Physics Scanning Modes Pulsed Wave Doppler
Published: 2016/09/27
Channel: Point of Care Ultrasound Geek
continuous wave of condensation technique
continuous wave of condensation technique
Published: 2011/03/30
Channel: brightvisionled
ROOT CANAL FILLING / Continuous Wave Technique
ROOT CANAL FILLING / Continuous Wave Technique
Published: 2009/12/08
Channel: 服部操
16A. Pulmonary regurgitation continuous wave doppler
16A. Pulmonary regurgitation continuous wave doppler
Published: 2014/12/29
Channel: Luke Howard
Hot Tips - Probe Positioning for a Continuous-wave Doppler Technique
Hot Tips - Probe Positioning for a Continuous-wave Doppler Technique
Published: 2013/11/01
Channel: Gulfcoast Ultrasound Institute
Continuous-Wave Doppler with GNURadio on a laptop
Continuous-Wave Doppler with GNURadio on a laptop
Published: 2014/05/03
Channel: sm313
OBIS Laser Demo: Continuous Wave (CW) Modulation
OBIS Laser Demo: Continuous Wave (CW) Modulation
Published: 2014/11/13
Channel: Coherent Inc
Master Houdini - Continuous Waves with Flip Fluids
Master Houdini - Continuous Waves with Flip Fluids
Published: 2014/05/03
Channel: FX HIVE
CW (continuous wave ) morse code demo at Kings County Radio Club.
CW (continuous wave ) morse code demo at Kings County Radio Club.
Published: 2013/02/13
Channel: HowardB2
Gold Slow Foxtrot - Continuous Reverse Wave Ballroom Dance Lesson
Gold Slow Foxtrot - Continuous Reverse Wave Ballroom Dance Lesson
Published: 2011/06/02
Channel: Andy Wong
River Into ocean Waimea Bay Hawaii continuous wave
River Into ocean Waimea Bay Hawaii continuous wave
Published: 2017/02/12
Channel: David Butcher
CW Radar
CW Radar
Published: 2015/06/22
Channel: Vidya-mitra
Continuous Wave Technique
Continuous Wave Technique
Published: 2014/09/19
Channel: Takashi UMEDA D.D.S.
24GHz doppler radar (CW - Continuous Wave) - first test...
24GHz doppler radar (CW - Continuous Wave) - first test...
Published: 2016/04/27
Channel: sb5100MoD
Continuous Wave Condensation Technique
Continuous Wave Condensation Technique
Published: 2013/07/06
Channel: Carlos Vidal Tudela
elements™free - Cordless Continuous Wave Obturation
elements™free - Cordless Continuous Wave Obturation
Published: 2017/03/28
Channel: Kerr Corporation
Real-time absolute frequency measurement of continuous-wave terahertz radiation based on dual...
Real-time absolute frequency measurement of continuous-wave terahertz radiation based on dual...
Published: 2015/04/23
Channel: ScienceVio
Maxillary first molar. 4 root canals. Continuous wave condensation technique with microscope.
Maxillary first molar. 4 root canals. Continuous wave condensation technique with microscope.
Published: 2014/01/24
Channel: Pablo Salmerón
右上6 Continuous Wave Condensation Technique
右上6 Continuous Wave Condensation Technique
Published: 2017/07/10
Channel: 柳沢歯科医院
Kernis: Symphony in Waves - 1. Continuous Wave
Kernis: Symphony in Waves - 1. Continuous Wave
Published: 2017/01/23
Channel: Gerard Schwartz - Topic
Lightbulb + Continuous Wave Tesla Coil
Lightbulb + Continuous Wave Tesla Coil
Published: 2014/11/08
Channel: TESLA SCIENCE
Elements Obturation Unit - Continuous Wave Obturation
Elements Obturation Unit - Continuous Wave Obturation
Published: 2012/03/12
Channel: AxisDental
Continuous Wave Technique (Nex)
Continuous Wave Technique (Nex)
Published: 2015/10/08
Channel: Takashi UMEDA D.D.S.
Symphony in Waves: I. Continuous Wave
Symphony in Waves: I. Continuous Wave
Published: 2014/09/24
Channel: Various Artists - Topic
Keith Welborn Kalahari Body Boarding on Surf Continuous Wave Feb 2013
Keith Welborn Kalahari Body Boarding on Surf Continuous Wave Feb 2013
Published: 2013/02/20
Channel: William Herzog
Frequency-Modulated Continuous-Wave (FMCW) Radar
Frequency-Modulated Continuous-Wave (FMCW) Radar
Published: 2011/08/16
Channel: wolframmathematica
Continuous Wave & Hybrid Techs - Step-by-Step Sequence: Advanced Endodontics: Dr Cliff Ruddle
Continuous Wave & Hybrid Techs - Step-by-Step Sequence: Advanced Endodontics: Dr Cliff Ruddle
Published: 2012/10/03
Channel: Advanced Endodontics
Kelly Slater surfing river rapid wave at Waimea Bay Hawaii 2011.wmv
Kelly Slater surfing river rapid wave at Waimea Bay Hawaii 2011.wmv
Published: 2011/10/03
Channel: MrGoodone67
Retreatment #14 Continuous Wave Condensation Technique
Retreatment #14 Continuous Wave Condensation Technique
Published: 2015/12/05
Channel: S 精密歯科センター 御所南しげおかデンタルオフィス
continuous wave
continuous wave
Published: 2016/11/10
Channel: Baylee Robichaux
Meta Biomed EQ-V Instructional Video
Meta Biomed EQ-V Instructional Video
Published: 2017/02/22
Channel: Yohan Choe
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WIKIPEDIA ARTICLE

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A continuous wave or continuous waveform (CW) is an electromagnetic wave of constant amplitude and frequency; almost always a sine wave, that for mathematical analysis is considered to be of infinite duration. Continuous wave is also the name given to an early method of radio transmission, in which a sinusoidal carrier wave is switched on and off. Information is carried in the varying duration of the on and off periods of the signal, for example by Morse code in early radio. In early wireless telegraphy radio transmission, CW waves were also known as "undamped waves", to distinguish this method from damped wave signals produced by earlier spark gap type transmitters.

Radio[edit]

Transmissions before CW[edit]

Very early radio transmitters used a spark gap to produce radio-frequency oscillations in the transmitting antenna. The signals produced by these spark-gap transmitters consisted of strings of brief pulses of sinusoidal radio frequency oscillations which died out rapidly to zero, called damped waves. The disadvantage of damped waves was that their energy was spread over an extremely wide band of frequencies; they had wide bandwidth. As a result, they produced electromagnetic interference (RFI) that spread over the transmissions of stations at other frequencies.

This motivated efforts to produce radio frequency oscillations that decayed more slowly; had less damping. There is an inverse relation between the rate of decay (the time constant) of a damped wave and its bandwidth; the longer the damped waves take to decay toward zero, the narrower the frequency band the radio signal occupies, so the less it interferes with other transmissions. As more transmitters began crowding the radio spectrum, reducing the frequency spacing between transmissions, government regulations began to limit the maximum damping or "decrement" a radio transmitter could have. Manufacturers produced spark transmitters which generated long "ringing" waves with minimal damping.

Transition to CW[edit]

It was realized that the ideal radio wave for radiotelegraphic communication would be a sine wave with zero damping, a continuous wave. An unbroken continuous sine wave theoretically has no bandwidth; all its energy is concentrated at a single frequency, so it doesn't interfere with transmissions on other frequencies. Continuous waves could not be produced with an electric spark, but were achieved with the vacuum tube electronic oscillator, invented around 1913 by Edwin Armstrong and Alexander Meissner. After World War I, transmitters capable of producing continuous wave, the Alexanderson alternator and vacuum tube oscillators, became widely available.

Damped wave spark transmitters were replaced by continuous wave vacuum tube transmitters around 1920, and damped wave transmissions were finally outlawed in 1934.

Key clicks[edit]

In order to transmit information, the continuous wave must be turned off and on with a telegraph key to produce the different length pulses, "dots" and "dashes", that spell out text messages in Morse code, so a "continuous wave" radiotelegraphy signal consists of pulses of sine waves with a constant amplitude interspersed with gaps of no signal.

In on-off carrier keying, if the carrier wave is turned on or off abruptly, communications theory can show that the bandwidth will be large; if the carrier turns on and off more gradually, the bandwidth will be smaller. The bandwidth of an on-off keyed signal is related to the data transmission rate as: where is the necessary bandwidth in hertz, is the keying rate in signal changes per second (baud rate), and is a constant related to the expected radio propagation conditions; K=1 is difficult for a human ear to decode, K=3 or K=5 is used when fading or multipath propagation is expected.[1]

The spurious noise emitted by a transmitter which abruptly switches a carrier on and off is called key clicks. The noise occurs in the part of the signal bandwidth further above and below the carrier than required for normal, less abrupt switching. The solution to the problem for CW is to make the transition between on and off to be more gradual, making the edges of pulses soft, appearing more rounded, or to use other modulation methods (e.g. phase modulation). Certain types of power amplifiers used in transmission may aggravate the effect of key clicks.

Persistence of radio telegraphy[edit]

A commercially manufactured paddle for use with electronic keyer to generate Morse code

Early radio transmitters could not be modulated to transmit speech, and so CW radio telegraphy was the only form of communication available. CW still remains a viable form of radio communication many years after voice transmission was perfected, because simple, robust transmitters can be used, and because its signals are the simplest of the forms of modulation able to penetrate interference. The low bandwidth of the code signal, due in part to low information transmission rate, allows very selective filters to be used in the receiver, which block out much of the radio noise that would otherwise reduce the intelligibility of the signal.

Continuous-wave radio was called radiotelegraphy because like the telegraph, it worked by means of a simple switch to transmit Morse code. However, instead of controlling the electricity in a cross-country wire, the switch controlled the power sent to a radio transmitter. This mode is still in common use by amateur radio operators.

In military communications and amateur radio the terms "CW" and "Morse code" are often used interchangeably, despite the distinctions between the two. Aside from radio signals, Morse code may be sent using direct current in wires, sound, or light, for example. For radio signals, a carrier wave is keyed on and off to represent the dots and dashes of the code elements. The carrier's amplitude and frequency remains constant during each code element. At the receiver, the received signal is mixed with a heterodyne signal from a BFO (beat frequency oscillator) to change the radio frequency impulses to sound. Though most commercial traffic has now ceased operation using Morse it is still popular with amateur radio operators. Non-directional beacons used in air navigation use Morse to transmit their identifier.

Radar[edit]

Morse code is all but extinct outside the amateur service, so in non-amateur contexts the term CW usually refers to a continuous-wave radar system, as opposed to one transmitting short pulses. Some monostatic (single antenna) CW radars transmit and receive a single (nonswept) frequency, often using the transmitted signal as the local oscillator for the return; examples include police speed radars and microwave-type motion detectors and automatic door openers. This type of radar is effectively "blinded" by its own transmitted signal to stationary targets; they must move toward or away from the radar quickly enough to create a Doppler shift sufficient to allow the radar to isolate the outbound and return signal frequencies. This kind of CW radar can measure range rate but not range (distance).

Other CW radars linearly or pseudo-randomly "chirp" (frequency modulate) their transmitters rapidly enough to avoid self-interference with returns from objects beyond some minimum distance; this kind of radar can detect and range static targets. This approach is commonly used in radar altimeters, in meteorology and in oceanic and atmospheric research. The landing radar on the Apollo Lunar Module combined both CW radar types.

CW bistatic radars use physically separate transmit and receive antennas to lessen the self-interference problems inherent in monostatic CW radars.

Laser physics[edit]

In laser physics and engineering, "continuous wave" or "CW" refers to a laser that produces a continuous output beam, sometimes referred to as "free-running," as opposed to a q-switched, gain-switched or modelocked laser, which has a pulsed output beam.

The continuous wave semiconductor laser was invented by Japanese physicist Izuo Hayashi in 1970.[citation needed] It led directly to the light sources in fiber-optic communication, laser printers, barcode readers, and optical disc drives, commercialized by Japanese entrepreneurs,[2] and opened up the field of optical communication, playing an important role in future communication networks.[3] Optical communication in turn provided the hardware basis for internet technology, laying the foundations for the Digital Revolution and Information Age.[4]

See also[edit]

References[edit]

  1. ^ L. D. Wolfgang, C. L. Hutchinson (ed) The ARRL Handbook for Radio Amateurs, Sixty Eighth Edition, (ARRL, 1991) ISBN 0-87259-168-9, pages 9-8, 9-9
  2. ^ Johnstone, Bob (2000). We were burning : Japanese entrepreneurs and the forging of the electronic age. New York: BasicBooks. p. 252. ISBN 9780465091188. 
  3. ^ S. Millman (1983), A History of Engineering and Science in the Bell System, page 10, AT&T Bell Laboratories
  4. ^ The Third Industrial Revolution Occurred in Sendai, Soh-VEHE International Patent Office, Japan Patent Attorneys Association

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