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# Modulasi Frekuensi Pertemuan 4 - PowerPoint PPT Presentation

Matakuliah : H0122 / Dasar Telekomunikasi Tahun : 2008. Modulasi Frekuensi Pertemuan 4. Learning Outcomes. Mahasiswa dapat menjelaskan teknik modulasi frekuensi dan karakteristiknya. Outline Materi. Prinsip Modulasi Frekuensi Bandwidth Hubungan dengan Modulasi Fasa. Angle Modulation.

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Tahun : 2008

### Modulasi FrekuensiPertemuan 4

Mahasiswa dapat menjelaskan teknik modulasi frekuensi dan karakteristiknya.

• Prinsip Modulasi Frekuensi

• Bandwidth

• Hubungan dengan Modulasi Fasa

• The angle modulation can be expressed mathematically as:

m(t) = Vccos [ωct + (t)]

• m(t) = angle modulated wave

• Vc = peak carrier amplitude (Volt)

• (t ) = instantaneous phase deviation (radians)

• The magnitude of the frequency (f) and phase deviation ()is proportional to the amplitude of the modulating signal, Vm and the rate at which the changes are occurring is equal to the modulating signal frequency, fm.

• 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.

• 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.

• 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 = fd / fm)

• The modulation index determines the number of significant pairs of sidebands in FM signals.

Kfis the frequency deviation sensitivity

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.

• Frequency modulation index is defined as

m = Kf Vm/ωm

• 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 /fm

Carrier

Modulating

signal

FM

PM

PM:

Jn (m) is the Bessel function of the first kind

Spektrum

• m = modulation index

• Vc = peak amplitude of the unmodulated carrier

• J0(m) = carrier component

• J1(m) = first set of side frequencies displaced from

the carrier by ωm

• J2(m) = second set of side frequencies displaced

from the carrier by 2ωm

• Jn(m) = nth set of side frequencies displaced from

the carrier by nωm

FM modulator: f = 10 kHz, fm = 10 kHz, Vc = 10 V, fc = 500 kHz, m=1

• Low-index modulation (narrowband FM)

• m <1 (fm>>f), B = 2fm

• High-index modulation (wideband FM)

• m >10 (f >>> fm), B = 2fm

• Actual bandwidth

• B = 2nfm

• (use Bessel table, n = number of significant sidebands)

• Carson’s rule (approx 98% of power)

• B = 2 (f + fm)

• Δf = peak frequency deviation

• fm = modulating frequency

• 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

Frequency modulator

Direct

FM wave

Vccos(2πfct)

Kf is the deviation sensitivity

Frequency Modulator

• Telah dipelajari karakteristik modulasi sudut

• Telah dipelajari modulasi frekuensi

• Telah dipelajari peran sidebands.