damped wave Damping is an influence within or upon an oscillatory system that has the effect of reducing or preventing its oscillation. In physical systems, damping is produced by processes that dissipate the energy stored in the oscillation. Examples inc ...

was an early method of

radio transmission Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitt ...

produced by the first

radio transmitter In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the ...

s (

spark gap transmitter A spark-gap transmitter is an obsolete type of radio transmitter which generates radio waves by means of an electric spark."Radio Transmitters, Early" in Spark-gap transmitters were the first type of radio transmitter, and were the main type use ...

s) which consisted of a series of damped

radio wave Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (short ...

s. Information was carried on this signal by

telegraphy Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas p ...

, turning the transmitter on and off ( on-off keying) to send messages in

Morse code Morse code is a method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code is named after Samuel Morse, one of ...

. Damped waves were the first practical means of radio communication, used during the

wireless telegraphy Wireless telegraphy or radiotelegraphy is transmission of text messages by radio waves, analogous to electrical telegraphy using cables. Before about 1910, the term ''wireless telegraphy'' was also used for other experimental technologies for ...

era which ended around 1920. In

radio engineering Broadcast engineering is the field of electrical engineering, and now to some extent computer engineering and information technology, which deals with radio and television broadcasting. Audio engineering and RF engineering are also essential par ...

it is now generally referred to as "Class B" emission. Such transmissions have a wide

bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...

and generate electrical "noise" (

electromagnetic interference Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electros ...

) which interferes with other radio transmissions. Because of their potential to cause interference and their resulting wasteful use of

radio spectrum The radio spectrum is the part of the electromagnetic spectrum with frequencies from 0 Hz to 3,000 GHz (3 THz). Electromagnetic waves in this frequency range, called radio waves, are widely used in modern technology, particula ...

resources, there is an international prohibition against the use of class B damped wave radio emissions (except in the USA under Part 15: "§15.521 Technical requirements applicable to all UWB devices. (i) The prohibition in §2.201(f) and 15.5(d) of this chapter against Class B (damped wave) emissions does not apply to UWB devices operating under this subpart."), established by the

International Telecommunication Union The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Unio ...

in 1938. individual nations enforce this prohibition in their communication laws. In the United States this is implemented in regulations of the Federal Communications Commission: However the definition of "damped waves" in these regulations is unclear when applied to modern technology, and recently there have been moves to amend this prohibition to exempt emerging radio technologies such as ultra-wideband transmission systems. {{cite web , title = Notice of Inquiry: Revision of Part 15 of the Commission's Rules Regarding Ultra-Wideband Transmission Systems , work = ET Docket No. 98-153 , publisher = US Federal Communications Commission , date = August 20, 1998 , url = http://sss-mag.com/pdf/UWBRULES.pdf , accessdate = 2010-03-04

References

External links

Sparks Telegraph Key Review
A complete listing with photos of damped wave telegraph keys (spark keys) by manufacturer.

FCC rules where "Type B damped wave emissions" are forbidden. Radio modulation modes

See also

References

External links