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

  • Thread starter Thread starter LostInSpace
  • Start date Start date
  • Tags Tags
    Modulation Signal
AI Thread Summary
Amplitude Shift Keying (ASK) and Phase Shift Keying (PSK), including Quadrature Amplitude Modulation (QAM), require bandwidth because the modulation alters the signal's characteristics, leading to variations in frequency. Although the carrier frequency remains constant, the modulation introduces changes in amplitude and phase that result in different instantaneous frequencies. This variation in frequency over time necessitates a broader bandwidth to accommodate the signal's changes. The slope of the signal, represented as dV/dT, differs from that of an unmodulated sine wave, indicating that the signal is not constant. Therefore, bandwidth is essential for effectively transmitting modulated signals.
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.
 

Thread 'Query on Isentropic relationships (such as PV^gamma = constant)'

Hi all, I have a question. So from the derivation of the Isentropic process relationship PV^gamma = constant, there is a step dW = PdV, which can only be said for quasi-equilibrium (or reversible) processes. As such I believe PV^gamma = constant (and the family of equations) should not be applicable to just adiabatic processes? Ie, it should be applicable only for adiabatic + reversible = isentropic processes? However, I've seen couple of online notes/books, and...
View full post »
Thread 'How can I find the cleanout for my building drain?'

Thread 'How can I find the cleanout for my building drain?'

I am a long distance truck driver, but I recently completed a plumbing program with Stratford Career Institute. In the chapter of my textbook Repairing DWV Systems, the author says that if there is a clog in the building drain, one can clear out the clog by using a snake augur or maybe some other type of tool into the cleanout for the building drain. The author said that the cleanout for the building drain is usually near the stack. I live in a duplex townhouse. Just out of curiosity, I...
View full post »

Thread 'Dry sump pump issue'

I have an engine that uses a dry sump oiling system. The oil collection pan has three AN fittings to use for scavenging. Two of the fittings are approximately on the same level, the third is about 1/2 to 3/4 inch higher than the other two. The system ran for years with no problem using a three stage pump (one pressure and two scavenge stages). The two scavenge stages were connected at times to any two of the three AN fittings on the tank. Recently I tried an upgrade to a four stage pump...
View full post »

Similar threads

Modulation & demodulation of GPS output digital data
Replies
10
Views
1K
Why does increasing the message bandwidth decrease the FM bandwidth?
Replies
5
Views
1K
Why AM wave is multiplication of carrier and message signal?
Replies
4
Views
3K
AM, FM modulation, sidebands question
Replies
15
Views
4K
Understand the concept of bandwidth
Replies
24
Views
3K
A Imperfectly Phase-Modulated Light / Residual Amplitude Modulation
Replies
2
Views
1K
Frequency Shift Key Modulation: how are the carrier frequencies chosen
Replies
5
Views
2K
I Why is saxophone growling produced by modulation of the sound waves?
2
Replies
92
Views
5K
Frequency of Modulated Signal: Carrier vs Message
Replies
3
Views
3K
What causes the capture effect in FM modulation?
Replies
5
Views
10K

Hot Threads

Recent Insights

Back
Top