![]() In noncoherent BFSK, there may be discontinuity in the phase when one signal element ends and the next begins. There are two implementations of BFSK: noncoherent and coherent. It can be shown that the minimum value should be at least S for the proper operation of modulation and demodulation. What should be the minimum value of 2Δ f ? In the above figure, we have chosen a value greater than (1 + d )S. If the difference between the two frequencies is 2Δf, then the required bandwidth is We can think of FSK as two ASK signals, each with its own carrier frequency ( f1 or f2). Again, the carrier signals are only simple sine waves, but the modulation creates a nonperiodic composite signal with continuous frequencies. The same figure also shows the bandwidth of FSK. The difference between the two frequencies is 2Δf. Both f1 and f2 are Δf apart from the midpoint between the two bands. The following figure shows how we can simply implement binary ASK.Īs the above figure shows, the middle of one bandwidth is f1 and the middle of the other is f2. However, the simple ideas behind the implementation may help us to better understand the concept itself. The complete discussion of ASK implementation is beyond the scope of this article. We can shift the resulting bandwidth to match what is available. This is in fact the most important advantage of digital-to-analog conversion. This means if we have a bandpass channel available, we can choose our f c so that the modulated signal occupies that bandwidth. The middle of the bandwidth is where f c, the carrier frequency, is located. The most important point here is the location of the bandwidth. The formula shows that the required bandwidth has a minimum value of S and a maximum value of 2S. This means that the bandwidth can be expressed as shown, where S is the signal rate and the B is the bandwidth. However, there is normally another factor involved, called d, which depends on the modulation and filtering process. As we expect, the bandwidth is proportional to the signal rate (baud rate). This signal has a continuous set of frequencies. ![]() Although the carrier signal is only one simple sine wave, the process of modulation produces a nonperiodic composite signal. The previous figure also shows the bandwidth for ASK. Binary amplitude shift keying Bandwidth for ASK
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