Instructions for Frequency Modulation (FM)
- Step 1: Click on 'Generate Message' button to generate input message signal
- Step 2: Then click on 'Generate Carrier' button to generate carrier signal. The carrier frequency has to be more than the message frequency and You can change frequencies using sliders
- Step 3: Click on 'Generate Frequency Modulated Signal' button to generate Frequency Modulated Signal
- Step 4: Click the 'Show Frequency Spectrums' button to view the FM spectra.
- Here, β represents the frequency modulation index, given by β = kf*Am/fm, where Am is the amplitude of the message signal (assumed to be fixed), fm is its frequency, and kf is the frequency sensitivity
1Hz
Step 1:
10Hz
Step 2:
Kf (frequency sensitivity):
50
Step 3:
Step 4:
Frequency Demodulation
Fig 2: Frequency Demodulation using a PLL
The diagram shows the demodulation of an FM signal using a Phase-Locked Loop (PLL). A PLL is an electronic system that synchronizes the phase of a local oscillator with the phase of the incoming FM signal, allowing it to track variations in the instantaneous frequency.
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FM Signal Input: \( s(t) = A_c \cos\left[ 2\pi f_c t + 2\pi K_f \int m(\tau) d\tau \right] \).
This represents the received frequency-modulated signal, where:
- \( A_c \) = carrier amplitude
- \( f_c \) = carrier frequency
- \( K_f \) = frequency sensitivity of the modulator
- \( m(t) \) = message (modulating) signal
- Phase Detector (PD): Compares the incoming FM signal with the VCO output and generates an error voltage proportional to their phase difference. This error voltage reflects the instantaneous frequency deviation of the FM signal.
- Loop Filter: Filters and smooths the output of the phase detector, reducing high-frequency noise and maintaining stable PLL operation.
- Voltage-Controlled Oscillator (VCO): Varies its output frequency based on the filtered error voltage, thereby tracking the instantaneous frequency variations of the incoming FM signal.
Demodulated FM Output: The filtered error voltage produced by the loop represents the original message signal \( m(t) \), thereby recovering the baseband information from the FM signal.
