This question was previously asked in

ALP CBT 2 Electronic Mechanic Previous Paper: Held on 21 Jan 2019 Shift 1

Option 1 : A finite number of amplitude are used

CT 1: Network Theory 1

11608

10 Questions
10 Marks
10 Mins

Digital Modulation Techniques:

1) Amplitude shift key

2) Frequency shift key

3) Phase Shift key

4) QAM

__ASK System__:

1. In the ASK modulation scheme, a finite number of amplitudes are used for binary 1 and 0 transmission.

2. For ASK Transmitter on-off keying is used.

3. In Amplitude Shift Keying (ASK) binary 1 is represented with the presence of carrier and binary 0 is represented with the absence of the carrier.

1 : s1(t) = Ac cos 2πfct

0 : s2 (t) = 0

Hence,

ASK = [± 10 V, 0, ± 10 V, ± 10 V, ± 10 V, ± 10 V, 0, 0]

__FSK (Frequency Shift Keying)__:

In FSK (Frequency Shift Keying) binary 1 is represented with a high-frequency carrier signal and binary 0 is represented with a low-frequency carrier, i.e. In FSK, the carrier frequency is switched between 2 extremes.

For binary ‘1’ → S1 (A) = Acos 2π fHt

For binary ‘0’ → S2 (t) = A cos 2π fLt . The constellation diagram is as shown:

__PSK(Phase Shift Keying)__:

In PSK (phase shift keying) binary 1 is represented with a carrier signal and binary O is represented with 180° phase shift of a carrier

For binary ‘1’ → S_{1} (A) = Acos 2π f_{c}t

For binary ‘0’ → S_{2} (t) = A cos (2πf_{c}t + 180°) = - A cos 2π f_{c}t

The Constellation Diagram Representation is as shown: