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F m-modulation-and-demodulation
Frequency modulation (FM) involves varying the frequency of a carrier wave based on the instantaneous amplitude of a modulating signal. FM provides improved signal-to-noise ratio and less interference between stations compared to amplitude modulation, but uses much more bandwidth and requires more complex transmitter and receiver circuits. The document discusses modulation index, frequency deviation, Carson's bandwidth rule for FM signals, and includes a circuit diagram for a frequency modulator and demodulator that is used to generate and recover a message signal.
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F m-modulation-and-demodulation
- 1. DESIGN OF FM MODULATOR AND DEMODULATOR
- 2. INTRODUCTION It is aprocess in which the frequency of the carrier is varied in accordance with the instantaneous value of modulating voltage. The amount of change in frequency is determined by the amplitude of the modulating signal.
- 4. FREQUENCY MODULATION VS AMPLITUDEMODULATION The main advantages of FM over AM are: • Improved signal to noise ratio (about 25dB). • Smaller geographical interference between neighbouring stations. • Less radiated power. • Well defined service areas for given transmitter power. Disadvantages of FM: • Much more Bandwidth (as much as 20 times as AM). • More complicated receiver and transmitter.
- 5. • MODULATION INDEX: It is defined as the ratio of frequency deviation to the frequency of the modulating signal. m = ΔF/f m • FREQUENCY DEVIATION : The frequency deviation ΔF represents the maximum shift between the modulated signal frequency, over and under the frequency of the carrier ΔF = (Fmax-Fmin)/2
- 6. BANDWIDTH OF FM Carson'sBandwidth Rule states that 98% of the signal power is contained within a bandwidth equal to the deviation frequency, plus the modulation frequency doubled, i.e.: • The bandwidth of a frequency modulated signal varies with both deviation and modulating frequency. • The frequency modulation bandwidth increases with modulation frequency but it is not directly proportional to it.
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- 9. CONCLUSION We have designeda Frequency Generator which can produce Square, Triangular and Sinusoidal waveforms up to 15 kHz (approx..) frequency. When the Sinusoidal message signal is fed to the Frequency Modulator circuit we get a frequency modulated output. The modulated wave when passed through the Frequency Demodulator circuit we get back the message signal in a distorted form.
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