It was discovered that by applying a modulation index of 0.5, phase continuity could be maintained and FSK schemes such as MSK (Minimum Shift Keying) and GFSK (Gaussian Frequency Shift Keying) could be realised.Phase-shift keying ( PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency reference signal (the carrier wave). However without careful timing, phase discontinuities will be present extending the sidebands into neighbouring channels causing interference across the spectrum.
This makes FSK suitable for battery powered operation.įSK can be implemented by switching 2 oscillators of different frequency in response to our digital signal. A further advantage of FSK is that since there are no amplitude changes, non-linear amplifiers that are more power efficient can be used.
Similar to FM, FSK is more resistant to noise than ASK since information is carried by frequency shifts instead of amplitude shifts. This is known as Frequency Shift Keying or FSK. If instead of a continuous signal we input voltage pulses, the result is a radio wave carrier with shifts in frequency corresponding to the “HIGH” and “LOW” level in our signal. By varying the frequency of the radio wave carrier with our message signal we can transmit analogue information such as a voice signal. In the article, Analogue modulation, we talked about frequency modulation or FM. This is known as Amplitude Shift Keying or ASK. If instead of a continuous signal we input voltage pulses, the result is a radio wave carrier with shifts in amplitude corresponding to the “HIGH” and “LOW” level in our signal. The result is a radio wave carrier, s(t) with amplitude fluctuations. By varying the amplitude of the radio wave carrier with our message signal, m(t) we can transmit analogue information such as a voice signal. In the article, Analogue modulation, we talked about amplitude modulation or AM. The 3 main methods used to modulate digital signals are amplitude shift keying (ASK), frequency shift keying (FSK) and phase shift keying (PSK). If a similar technique is applied to digital signals, the output will be amplitude, frequency or phase shifts (where each shift is a transition from 0 to 1 and 1 to 0). In analogue communication, we change the radio carrier’s amplitude (AM), frequency (FM) or phase (PM) in response to the input signal. How do we transmit a bit stream?Ī bit stream is just a signal with transitions from LOW to HIGH voltage levels instead of continuous variations.
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In the next section, we will talk about how to modulate these bit streams so they can be transmitted over radio waves. This is amplified and fed into a loudspeaker.ĭigital communications taking place between computersĭigital communication over radio include digital television broadcasts (DVB-S2, ISDB etc.), digital radio (DAB etc.), GPS systems and mobile phone communication. The signal is amplified and demodulation extracts the superimposed voice signal from the carrier. The modulated radio frequency signal is amplified and delivered to the station antenna for transmission.Īt the receiver the radio wave is picked by the receiver antenna and converted back to the radio frequency signal. For this Frequency Modulation (FM) or Amplitude modulation (AM) is used. This signal is amplified and passed to the modulator where it is superimposed onto a radio frequency carrier. The microphone converts the voice into a continuously varying electrical signal. Difference between analogue and digital communication Example of analogue communicationĪn example of an analogue communication system is a typical AM or FM radio broadcast.
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Moving on from this topic, in this article we will discuss digital communication and digital modulation techniques and how they are used to transport non-continuous signals such as binary or serial data. Various techniques such as AM, FM and PM were discussed. Thus the voice signal is recovered, amplified and can be fed to a loudspeaker. Analogue modulation takes a continuously varying signal such as voice signal and superimposes it onto a radio frequency carrier and demodulation at the receiver separates and extracts the signal. In another article, Analogue modulation, we talked about analogue communication systems.
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