In amplitude modulation (AM), when two signals of slightly different frequencies (f1 and f2) are combined, an interference phenomenon called beats occurs. This results in a new signal with an amplitude that varies sinusoidally with a frequency (fbeat) equal to the difference between the two original frequencies (fbeat = |f1 – f2|). The resulting signal’s amplitude envelope frequency (fbeat) and the beat frequency are inversely related to the difference in the original frequencies.
Beats in Amplitude Modulation
Amplitude modulation (AM) is a modulation technique in which the amplitude of the carrier wave is varied in accordance with the modulating signal. The resulting AM wave contains sidebands that are located above and below the carrier frequency.
The beat frequency is the difference between the frequencies of the two sidebands. It is equal to twice the modulating frequency.
The beat frequency can be used to demodulate the AM wave. This is done by using a filter to remove one of the sidebands. The remaining sideband is then demodulated to recover the original modulating signal.
The bandwidth of an AM wave is twice the bandwidth of the modulating signal. This is because the AM wave contains two sidebands, each of which has a bandwidth equal to the bandwidth of the modulating signal.
The power of an AM wave is proportional to the square of the amplitude of the modulating signal. This is because the power of a wave is proportional to the square of its amplitude.
The following table summarizes the key characteristics of AM waves:
| Characteristic | Value |
|---|---|
| Carrier frequency | fc |
| Modulating frequency | fm |
| Beat frequency | 2fm |
| Bandwidth | 2fm |
| Power | Proportional to the square of the amplitude of the modulating signal |
Question 1:
What constitutes beats in the context of amplitude modulation?
Answer:
Beats in amplitude modulation (AM) refer to periodic fluctuations in the amplitude of the modulated wave, resulting from the interference of two or more waves with slightly different frequencies.
Question 2:
How does the beat frequency relate to the carrier and modulating frequencies in AM?
Answer:
The beat frequency in AM is equal to the difference between the carrier frequency and the modulating frequency, creating a low-frequency oscillation superimposed on the carrier wave.
Question 3:
What is the significance of beats in AM systems?
Answer:
Beats in AM systems are important for synchronous detection, which allows the recovery of the original modulating signal from the modulated wave by filtering out the higher-frequency carrier.
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