What is Modulation?
Modulation is the process in which some characteristic of carrier wave is varied in accordance with instantaneous value of the message or modulating signal.
Sometimes we can say Modulation means a change of tone.
Modulation helps in noise immunity, attentuation and it depends on the physical medium.
Why Modulation is essential?
There are some problems with transmitting baseband signals:
1) Antennas are not effective in transmission at low frequencies.
2) Noise and interference at low frequencies.
3) For long distance transmissions.
4) To reduce signal power loss.
So Modulation helps in following ways:
1) Easier to transmit carrier at higher frequency
2) By modulating different signals to different frequency bands,they can be transmitted simultaneously over the same channel
3) Antennas can be smaller
4) Antennas and other components easier to design
5) Effective bandwidth utilization.
TYPES OF MODULATION
As there are two types of signals,so Modulation is also of two types:
ANALOG MODULATION AND TYPES
Amplitude modulation (AM): In this the voltage(amplitude) applied to the carrier is varied over time.“AM” radio band 500 to 1600 kHz.
Frequency modulation (FM):In this the frequency of the carrier waveform is varied in accordance with message signal.“FM” radio band 88 to 108 MHz
Phase modulation (PM): In this the phase of the carrier is varied with the instantaneous value of message signal.
FM and PM closely related.
DIGITAL MODULATION AND TYPES
Pulse Code Modulation
It is used to encode both digital and analog information in a binary way.
Complex forms of modulation are:
• QPSK (Quadrature Phase Shift Keying)
• FSK (Frequency Shift Keying)
• MSK (Minimum Shift Keying)
• QAM (Quadrature Amplitude Modulation)
This process of recovering the original signal coming from the sender end in modulating form. We can say that its function is opposite to that of modulation process. It is done at the receiver side.
Simply, retrieving the message signal from the carrier signal without damaging the message is Demodulation.
In all the cases ,generally the Carrier is at higher frequency than the message or modulating signal.
We will discuss about each and every type of modulation separately in detail in upcoming posts.