Sine waves are commonly used to represent signals in communication systems because they have simple and regular oscillatory behavior. While sine waves themselves do not inherently carry information, they serve as carriers for encoding information using modulation techniques.
In signal communication, the information is typically encoded by modifying one or more properties of the carrier wave. The two most common modulation techniques are amplitude modulation (AM) and frequency modulation (FM).
Amplitude Modulation (AM): In AM, the information is encoded by varying the amplitude of the carrier wave. The modulating signal, which contains the information to be transmitted, is used to alter the amplitude of the carrier wave. The variations in amplitude correspond to the variations in the original signal, allowing the information to be carried.
Frequency Modulation (FM): In FM, the information is encoded by varying the frequency of the carrier wave. The modulating signal is used to change the instantaneous frequency of the carrier wave. The variations in frequency correspond to the variations in the original signal, carrying the information.
In both AM and FM, the carrier wave itself is typically a sine wave with a fixed frequency and amplitude. The variations in amplitude or frequency encode the information, while the carrier wave provides the medium for transmitting the modulated signal.
It's important to note that the variations in amplitude or frequency do not change the fundamental nature of the carrier wave. The changes in these properties occur within the envelope of the carrier wave, allowing the encoded information to be extracted at the receiver using appropriate demodulation techniques.
So, to answer your question, in signal communication using modulation techniques, varying the amplitude or frequency of the carrier wave is how information is encoded, while the carrier wave itself maintains its basic properties such as wavelength and amplitude.