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Amplitude Modulation (AM), simulation with Python and NumPy
AM is one of the easiest modulation techniques, and as a result it was the first modulation to be used. Developed during the first quarter of the 20th century, the first AM trasnmission was done using a spark gap transmitter. Nowadays, this modulation technique is still used in shortwave radio or amateur radio. A classification of more modulation techniques can be found in this article.
AM Theory
The AM technique is an analog modulation which modifies the amplitude of the carrier signal according to the message signal (the modulation signal). Considering a carrier signal with amplitude A𝒸 and frequency f𝒸:
The AM signal is:
Where A x(t) is the modulation signal. Below, an example of an AM signal for a given modulation and carrier signal.
Modulation index
Taking the AM signal, we can derive the following expression:
Where m is the modulation index, which is defined as:
This index express the level of excursions which the AM signal to the level of the carrier signal. As an example, the following figure shows 2 AM signals for different modulation index. In the first signal, with a modulation index of 0.5, the modulation signal produces variation of…
