Continuous wave
Continuous wave (English for uninterrupted wave ) or continuous waveform , abbreviated to CW , denotes an undamped, i.e. time-constant, emitted wave .
At the beginning of radio and radio technology at the end of the 19th century, transmissions took place in the form of muffled , interrupted waves. The first functional transmitters for the wireless transmission of Morse code were electrical spark transmitters such as bang , shock and extinguishing spark transmitters . They transmitted by charging a capacitor alternately and then discharging it via the transmitter coil in the form of a spark breakdown. This repetitive process produced muffled, interrupted waves with regular pauses due to the charging. Therefore, as well as because of their very large bandwidth , the more frequent possible interferences due to insufficient frequency selection and the loud bang each time the transmission radio is set off, these devices were "dirty" transmitters from a later perspective.
At the beginning of the twentieth century, Valdemar Poulsen and Reginald Fessenden invented more modern types of transmitters, each with an electric arc transmitter and a machine transmitter, which emitted undamped waves. This marked the beginning of a new era not only in telegraphy , but also for the first time in the broadcasting of language and music; with the intermittently working spark transmitters, a usable transmission of sounds was not possible.
Typically, CW uses a narrow band signal so that all the energy is concentrated in a narrow spectrum. This means that CW transmissions have a long range even with low transmission power, as the signal can still be decoded using narrow-band filters even with a poor signal-to-noise ratio - the filter bandwidths can be up to 250 Hz or less.
Meaning as "continuous line"
A Morse key can be used to generate the dot character with a short press or the line character of the Morse code with a longer press . The term continuous wave was derived from this Morse line , because constant pressure leaves the antenna with constant transmission power . This is how the term continuous wave radar came about for a certain type of radar device : a radiated, unmodulated signal in the microwave range is reflected and partially intercepted again. Non-pulsating lasers are also called continuous wave or CW lasers . In particle accelerators , is spoken by CW or continuous wave, when the accelerated particle beam is not interrupted (pulsed).
literature
- Apurba Das: Signal Conditioning: An Introduction to Continuous Wave Communication and Signal Processing . Springer, 2012, ISBN 978-3-642-28818-0 .