Signal Modulation: Why Does ASK/PSK (QAM) Need Bandwidth?

  • Thread starter Thread starter LostInSpace
  • Start date Start date
  • Tags Tags
    Modulation Signal
Click For Summary
SUMMARY

Amplitude Shift Keying (ASK) and Phase Shift Keying (PSK), including Quadrature Amplitude Modulation (QAM), require bandwidth due to the variations in signal characteristics. The modulation alters the amplitude and phase, leading to changes in the signal's frequency components over time. This results in a non-constant frequency, as evidenced by the varying slope (dV/dT) compared to an unmodulated sine wave. Therefore, bandwidth is essential for accommodating these frequency shifts during modulation.

PREREQUISITES
  • Understanding of signal modulation techniques, specifically Amplitude Shift Keying (ASK) and Phase Shift Keying (PSK).
  • Knowledge of Quadrature Amplitude Modulation (QAM) principles.
  • Familiarity with frequency domain analysis and signal characteristics.
  • Basic concepts of bandwidth and its significance in communication systems.
NEXT STEPS
  • Research the mathematical foundations of Amplitude Shift Keying (ASK) and Phase Shift Keying (PSK).
  • Explore the implications of bandwidth in digital communication systems.
  • Study the differences between QAM and other modulation techniques like Frequency Shift Keying (FSK).
  • Learn about the impact of signal slope (dV/dT) on bandwidth requirements in modulated signals.
USEFUL FOR

Electrical engineers, telecommunications professionals, and students studying signal processing and communication systems will benefit from this discussion.

LostInSpace
Messages
21
Reaction score
0
How come a signal modulated using Amplitud Shift Keying and/or Phase Shift Keying (such as QAM) require a bandwidth? I mean, since the frequence is constant; only the amplitude and phase is changed.

Thanks in advance!
 
Engineering news on Phys.org
LostInSpace said:
I mean, since the frequence is constant
It is not constant! The slope dV/dT changes from that of the unmodulated sine wave. This means that for a small periods of time it is different frequencies.
 

Similar threads

Modulation & demodulation of GPS output digital data
  • · Replies 10 ·
Replies
10
Views
2K
Why does increasing the message bandwidth decrease the FM bandwidth?
  • · Replies 5 ·
Replies
5
Views
2K
AM, FM modulation, sidebands question
  • · Replies 15 ·
Replies
15
Views
5K
Understand the concept of bandwidth
  • · Replies 24 ·
Replies
24
Views
3K
Frequency Shift Key Modulation: how are the carrier frequencies chosen
  • · Replies 5 ·
Replies
5
Views
2K
Frequency of Modulated Signal: Carrier vs Message
  • · Replies 3 ·
Replies
3
Views
4K
What causes the capture effect in FM modulation?
  • · Replies 5 ·
Replies
5
Views
10K
Mosfet, Mesfet vs Bipolar transistors in RF circuits
  • · Replies 28 ·
Replies
28
Views
6K
Am vs Fm variable capacitor receiver, what is the difference?
  • · Replies 2 ·
Replies
2
Views
3K
Can someone give me a better intuition of bandwidth?
  • · Replies 23 ·
Replies
23
Views
2K