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Modulasi Frekuensi Pertemuan 4 Matakuliah: H0122 / Dasar Telekomunikasi Tahun: 2008

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Bina Nusantara 2 Mahasiswa dapat menjelaskan teknik modulasi frekuensi dan karakteristiknya. Learning Outcomes

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Bina Nusantara 3 Prinsip Modulasi Frekuensi Bandwidth Hubungan dengan Modulasi Fasa Outline Materi

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Bina Nusantara 4 Angle Modulation The angle modulation can be expressed mathematically as: m(t) = V c cos [ ω c t + (t)] m(t)= angle modulated wave V c = peak carrier amplitude (Volt) c = carrier radian frequency (rad/sec) (t )= instantaneous phase deviation (radians) The magnitude of the frequency ( f) and phase deviation ( ) is proportional to the amplitude of the modulating signal, V m and the rate at which the changes are occurring is equal to the modulating signal frequency, f m.

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Bina Nusantara 5 Frequency & Phase Modulation (FM & PM) are both forms of Angle Modulation. Because of its superior performance than AM, it is used extensively for commercial broadcasting radio broadcasting, television sound transmission, 2-way mobile radio, cellular radio, microwave and satellite communications systems. Angle Modulation

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Bina Nusantara 6 Frequency Modulation is the process of changing carrier frequency by the modulating signal while the carrier amplitude remains constant. As the modulating signal amplitude increases, the carrier frequency increases and vice versa. The amount of change in carrier frequency produced by the modulating signal is called Frequency Deviation ( f). Meanwhile, the change in phase is called Phase Deviation ( ) The deviation is proportional to the amplitude of the modulating signal. Frequency Modulation

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Bina Nusantara 7 FM produces pairs of sidebands spaced from the carrier in multiples of the modulating frequency. The modulation index m of FM signal is the ratio of the frequency deviation fd to the modulating frequency, fm (m = f d / f m ) The modulation index determines the number of significant pairs of sidebands in FM signals. Frequency Modulation

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Bina Nusantara 8 Frequency Modulation The frequency of a harmonic carrier signal is varied in such a way that the instantaneous frequency deviation i.e. the difference between the instantaneous frequency and the carrier frequency is linearly related to the size of the modulating signal at a given instant of time. K f is the frequency deviation sensitivity

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Bina Nusantara 9 Modulation Index Frequency modulation index is defined as m = Kf V m / ω m Frequency deviation which is the change in carrier when acted on by a modulating signal frequency is given by: Peak frequency shift in hertz Peak-to-peak frequency deviation of carrier swing Therefore m can be rewritten as m=Δf /f m

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Bina Nusantara 10 PM & FM Waveform FM PM Carrier Modulating signal

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Bina Nusantara 11 Spektrum Jn (m) is the Bessel function of the first kind FM: PM:

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Bina Nusantara 12 m=modulation index V c = peak amplitude of the unmodulated carrier J 0 (m)= carrier component J 1 (m)= first set of side frequencies displaced from the carrier by ω m J 2 (m)=second set of side frequencies displaced from the carrier by 2 ω m J n (m)=nth set of side frequencies displaced from the carrier by n ω m Spektrum

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Bina Nusantara 13 Spektrum FM modulator: f = 10 kHz, f m = 10 kHz, V c = 10 V, f c = 500 kHz, m=1

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Bina Nusantara 14 Bandwidth Low-index modulation (narrowband FM) m > f), B = 2f m High-index modulation (wideband FM) m >10 ( f >>> f m ), B = 2 f m Actual bandwidth B = 2nf m (use Bessel table, n = number of significant sidebands) Carson’s rule (approx 98% of power) B = 2 ( f + f m ) Δf = peak frequency deviation f m = modulating frequency

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Bina Nusantara 15 FM modulator = integrator followed by a PM Modulator FM Demodulator = PM demodulator followed by a differentiator PM Modulator = Differentiator followed by an FM Modulator PM Demodulator = FM demodulator followed by an integrator FM & PM Modulator

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Bina Nusantara 16 K f is the deviation sensitivity Modulating signal source Frequency modulator FM wave Direct V c cos(2πf c t) Frequency Modulator

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Bina Nusantara 17 Telah dipelajari karakteristik modulasi sudut Telah dipelajari modulasi frekuensi Telah dipelajari peran sidebands. Summary

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