Amplitude-shift keying

Amplitude shift keying (english amplitude - shift keying, abbreviated ASK) is a digital modulation. The amplitude of the carrier is changed in order to transmit different values. Amplitude is the simplest form of the so-called on-off keying ( OOK ), wherein the carrier is switched on and off to provide a 1 or a 0 is to be transmitted.

Instead of only two different amplitude values, a plurality of gradations can be used. This can be per symbol step several bits encode. If, for example, four different amplitudes in a signal on each of these two bits represent amplitude (symbols: 00, 01, 10 and 11).

Applications

An example of amplitude shift keying is the German DCF77 signal of the clock, which is also called atomic clock. Other countries have implemented this idea on other frequencies. Here is a long-wave carrier of 77.5 kHz is attenuated at one second intervals in amplitude to 25% of rated power. The beginning of the attenuation is used for accurate time synchronization, and the duration of the weakening (100 ms or 200 ms) represents one bit. Within a minute, you have collected enough bits to represent the date, time, leap second, standard time / daylight saving time and possibly other information.

Another example is the beacon for localization. The carrier is modulated with a first tone in the audio range (e.g., 1 kHz). This in turn subcarrier is modulated with a Morse code as an identifier of the beacon ( keyed ).

Overview: Modulator

AM | FM | PM | VM | SSB | SSBSC | DSBSC

ASK | G | GFSK | QPSK | QAM | OFDM | DMT | TCM | VSB

PWM | PAM | PFM | PPM (1) | PPM (2) | PCM

• Modulation (technology)
• Digital Signal Processing