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FM and AM in Radio Broadcasting

FM and AM in Radio Broadcasting. EECE 252 PROJECT SPRING 2014 Presented by: Peizhen Sun Nor Asma Mohd Sidik. INTRODUCTION. Radio broadcasting is a one-way wireless transmission that transmits audio (sound) through the air as radio waves from a transmitter to an antenna (i.e. receiver).

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FM and AM in Radio Broadcasting

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  1. FM and AM in RadioBroadcasting EECE 252 PROJECT SPRING 2014 Presented by: Peizhen Sun Nor AsmaMohdSidik

  2. INTRODUCTION • Radio broadcasting is a one-way wireless transmission that transmits audio (sound) through the air as radio waves from a transmitter to an antenna (i.e. receiver). • Broadcasting by the radio takes several forms including AM and FM stations. • FM transmits information (sound) by varying the frequency of the wave, while the amplitude remains constant. AM works by modulating the amplitude of the signal, while the frequency remains constant.

  3. OPERATING CONDITIONS • FM radio has a higher spectrum, with ranges between 88MHz to 108MHz. • AM radio operates at a lower spectrum, with ranges between 535kHz to 1605kHz. WHAT IS THE POSSIBLE MODE OF FAILURE? • Answer: Noise

  4. Project Goal • To find the effect of noise on the recovered signal in FM radio and AM radio. • To find the relationship between the frequency deviation and the noise sensitivity level in FM modulation.

  5. PROCEDURE

  6. Procedures • We ran a simulation in Matlab using a handel signal that is 5 seconds long. 1) RESAMPLING • We resampled the signal using a sampling frequency, Fs of 100kHz.

  7. 2) ADDING NOISE • 1dB signal-to-noise ratio (SNR) was added to the message signal using a Matlab function called ‘awgn’.

  8. 3) MODULATION • We modulated the message signal at the carrier frequency of 10kHz. The carrier frequency was chosen to be less than the Nyquist frequency (50kHz). • The FM coefficient, Kf, was initially set to 4000π. We changed the value of Kf to change the frequency deviation. where mp is the maximum value of message signal m(t)

  9. 4) DEMODULATION • We demodulated the signal through differentiation. This technique is also called the envelope detector.

  10. 5) FILTER OUT HIGH FREQUENCIES • The rectified output signal was passed through a low pass filter to remove the higher frequencies. We used a low pass filter of order 160 and a cutoff frequency of 0.0819 rad/s.

  11. The same procedures were repeated using different coefficients of Kf : i) Kf=2500π => ∆f =1000 ii) Kf=6500π => ∆f =2600 • For AM (DSB-C) radio, we used an in-class modulation code. We added the same 1dB SNR to the original message. The signal was resampled at 100kHz with a carrier frequency of 10kHz.

  12. RESULTS

  13. RESULTS

  14. Frequency Modulation (FM)

  15. Recovered signal for ∆f=1kHz Original signal (without noise) SNR =1dB with Kf=2500π

  16. Recovered signal for ∆f=2.6kHz Original signal (without noise) SNR =1dB with Kf=6500π

  17. Amplitude Modulation (AM)

  18. Recovered signal from AM SNR =1dB Original signal (without noise)

  19. CONCLUSION

  20. CONCLUSION • FM and AM radio have completely different working principles. For example, they have different bandwidths and energies. There is no fair comparison between FM and AM. • For FM: i) When the ∆f increases, the effect of 1dB of noise on the final recovered signal will decrease. ii) When the ∆f decreases, the effect of 1dB of noise on the final recovered signal will increase.

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