Amplitude Shift Keying (ASK) -Digital To Analog Conversion and Transmission Tutorials Part II

Amplitude Shift Keying (ASK)is implemented by changing the amplitude of a carrier signal to reflect amplitude levels in the digital signal.

For example: a digital “1” could not affect the signal, whereas a digital “0” would, by making it zero.

The line encoding will determine the values of the Analog waveform to reflect the digital data being carried.

Bandwidth of ASK

The bandwidth B of ASK is proportional to the signal rate S.
B = (1+d)S
“d” is due to modulation and filtering, lies between 0 and 1.


Binary amplitude shift keying




Implementation of binary ASK





Problem Example 1:

We have an available bandwidth of 100 kHz which spans from 200 to 300 kHz. What are the carrier frequency and the bit rate if we modulated our data by using ASK with d = 1?


Solution

The middle of the bandwidth is located at 250 kHz. This means that our carrier frequency can be at fc = 250 kHz. We can use the formula for bandwidth to find the bit rate (with d = 1 and r = 1).


Problem Example 2:

In data communications, we normally use full-duplex links with communication in both directions. We need to divide the bandwidth into two with two carrier frequencies, as shown in Figure below. The figure shows the positions of two carrier frequencies and the bandwidths. The available bandwidth for each direction is now 50 kHz, which leaves us with a data rate of 25 kbps in each direction.

Bandwidth of full-duplex ASK

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