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Frequency Modulation in Wireless Microphone System

Frequency Modulation in Wireless Microphone System. EECE 252 Project Spring 2012 Presented by: Haolin Wang, Muhamad Fuad Harun , Baihaqis Bahran. Introduction. Introduction.

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Frequency Modulation in Wireless Microphone System

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  1. Frequency Modulation in Wireless Microphone System EECE 252 Project Spring 2012 Presented by: HaolinWang, MuhamadFuadHarun, BaihaqisBahran

  2. Introduction

  3. Introduction One of the applications of frequency modulation in real life is the usage of a wireless microphone. Wireless Microphone System requires a wireless transmitter, and a wireless receiver. The wireless transmitter can be built into the microphone itself or connected by a short cable to a body pack transmitter. The wireless receiver is tuned to the same electromagnetic wavelength as the transmitter and is physically attached to an output device. Wireless Microphone System uses FM to transmit the signal.

  4. Project Goals • To apply the knowledge about Frequency Modulation learned in class • To investigate the possible modes of failure for Wireless FM Microphone System • To reach to aconclusion of how we can Reduce The Modes of Failure

  5. System Block Diagram

  6. Assumption and Focus • We assume that the channel is an all pass channel • We focus on two parameters of the system, the sampling rate and the frequency deviation (important parameter in FM transmission) and how they affect the output of the system (original voice signal) • Problems we ignore: Interference, random noise from the surrounding

  7. Method and Procedure

  8. Matlab: • Matlabwas used to record a 5 seconds long sound through the built-in microphone on the laptop and the sound was sampled at frequency 44100 Hz.

  9. Figure 1.1: The plot of the original sound in time.

  10. Resampling and Modulation • We resampled the sound signal with a higher sampling rate to provide more frequency spaces for modulation and demodulations. • The signal was modulated through direct FM modulation with a carrier frequency of 100 kHz.

  11. Resampled Signal in Frequency Domain

  12. Modulated Signal in Frequency Domain

  13. Demodulation • We demodulated the signal by using envelope detector • First we differentiate the modulated signal by using differentiator • Then we use a low pass filter to get the signal that we need

  14. Derivative of The Modulated Signal

  15. Low Pass Filter

  16. Demodulated Signal

  17. Demodulated Signal In Time Domain

  18. We repeat the same procedures with different values of Fs (sampling rate) and deltaF (frequency deviation) to observe the behavior of the system

  19. Results and Conclusion

  20. Results

  21. Default Configuration

  22. Audio Signal Graph

  23. Default Setting vs Setting 2

  24. Default Setting vs Setting 3

  25. Default Setting vs Setting 4

  26. Default Setting vs Setting 5

  27. Conclusion • In summary, we used the radio and played around with the parameters, Fs_Hi and DeltaF and compared the result (demodulated signal) with the original signal. • Apparently, an increase in Fs_Hi will amplify the arbitrary noise that appeared due to the approximation process of the differentiation. • A lower Fs_Hi will decrease the noise in the demodulated signal. An increase in DeltaF will decrease the noise significantly and a decrease in DeltaF results in an increase in noise and destruction of the original signal (i.e., when the demodulated signal is played, the original message cannot be heard).

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