Frequency Modulation and Application

Frequency Modulation and Application Submitted by: Darshil Shah (IU1241090051)Modulation Amplitude Modulation Pulse Wave Modulation Continuous Wave Modulation Linear Modulation NonLinear Modulation Frequency Modulation Phase ModulationWhat is frequency modulation? When the frequency of carrier wave is changed in accordance with the message signal, The process is called frequency modulation. In FM the carrier amplitude remain constant the carrier frequency varies It is a type of Angle modulation Why Frequency modulation is called nonlinearmodulation?FM modulation index • FM modulation index is equal to the ratio of the frequency deviation to the modulating frequency. • Thus the formula for the modulation index for FM is simply given by that shown below: Frequency Deviation Modulating Frequency And also,Significant Sidebands – Spectrum • The table below shows the number of significant sidebands for various modulation  No of sidebands  1% of unmodulated carrier Bandwidth 0.1 2 2fm 0.3 4 4fm 0.5 4 4fm 1.0 6 6fm 2.0 8 8fm 5.0 16 16fm 10.0 28 28fm Example: For  = 5, 16 sidebands (8 pairs).Types of FM Narrow band FM 1. Narrow band FM is defined as the situation where the modulation index  is small. 2. From the table of Bessel functions it may be seen that for small , (  0.3) there is only the carrier and significant sidebands, i.e. BW = 2fm. FM with   0.3 is referred to as narrowband FM (NBFM). 3. Maximum modulating frequency is usually 3kHz 4. maximum frequency deviation is =75 kHz.Types of FM Wide band FM 1. Wideband FM is defined as the situation where the modulation index  is larger. 2. For  > 0.3 there are more than 2 significant sidebands. As  increases the number of sidebands increases. This is referred to as wideband FM (WBFM). 3. Modulation frequencies extend from 30 Hz to 15 kHz. 4. Maximum permissible deviation is=75 kHz. 5. Wideband FM system need large bandwidth, typically 15 times that of narrowband FM system.Generation of FM using PM Integrator Carrier Oscillator Phase Modulator Modulating Wave x(t) FM Wave  x(t)dt Eccos(2fct)Advantages 1. Amplitude of the frequency modulated wave remains unaffected. 2. Large decrease in noise, hence increase in SN ratio. 3. Noise may reduce by increasing deviation. 4. Frequency allocation allows for a guard band which reduces adjacent channel interference. 5. Operate In Very high frequency (VHF).Disadvantages • FM has too much advantages besides it also has some disadvantages 1. FM wave can’t cover large area. 2. Transmitting receiving equipments for FM are complex costly. 3. A much wider channel, typically 200 kHz, is needed for FM.FM Radio FM radio uses a modulation index, m > 1, and this is called wideband FM. As its name suggests the bandwidth is much larger than AM. In national radio broadcasts using FM, the frequency deviation of the carrier  fc , is chosen to be 75kHz, and the information baseband is the high fidelity range 20Hz to 15kHz. BW of FM radio=2(75k+15k) =180khz Applications:Television Sound: In terrestrial TV broadcasts, the video information is transmitted using AM . However the sound information is transmitted using FM, in order to reduce possible interference between the video and sound signals. In this case, the maximum deviation of the carrier,  fc , is chosen to be 50kHz, and the information baseband is again the high fidelity range 20Hz to 15kHz. Therefore the bandwidth required for TV Sound is: BW Of TV Sound=2(50k+15k) =130khz Satellite TV. Some satellite TV transmissions broadcast an analogue video signal using FM. This helps to obtain an acceptable signal at the receiving station In this case, the maximum deviation of the carrier  fc , is chosen to be about 10 MHz, with a video baseband of around 5MHz. Therefore the bandwidth required for Satellite TV is: BW of satellite TV =2(10+5) =30Mhz

Frequency Modulation and Application Submitted by: Darshil Shah (IU1241090051) Modulation Pulse Wave Modulation Continuous Wave Modulation Amplitude Modulation Linear Modulation Non-Linear Modulation Frequency Modulation Phase Modulation What is frequency modulation? When the frequency of carrier wave is changed in accordance with the message signal, The process is called frequency modulation In FM the carrier amplitude remain constant the carrier frequency varies It is a type of Angle modulation Why Frequency modulation is called nonlinearmodulation? FM modulation index • FM modulation index is equal to the ratio of the frequency deviation to the modulating frequency • Thus the formula for the modulation index for FM is simply given by that shown below: Frequency Deviation Modulating Frequency And also, Significant Sidebands – Spectrum • The table below shows the number of significant sidebands for various modulation  0.1 0.3 0.5 1.0 2.0 5.0 10.0 No of sidebands  1% of unmodulated carrier 4 16 28 Bandwidth 2fm 4fm 4fm 6fm 8fm 16fm 28fm Example: For  = 5, 16 sidebands (8 pairs) Types of FM Narrow band FM Narrow band FM is defined as the situation where the modulation index  is small From the table of Bessel functions it may be seen that for small , (  0.3) there is only the carrier and significant sidebands, i.e BW = 2fm FM with   0.3 is referred to as narrowband FM (NBFM) Maximum modulating frequency is usually 3kHz maximum frequency deviation is =75 kHz Types of FM Wide band FM Wideband FM is defined as the situation where the modulation index  is larger For  > 0.3 there are more than significant sidebands As  increases the number of sidebands increases This is referred to as wideband FM (WBFM) Modulation frequencies extend from 30 Hz to 15 kHz Maximum permissible deviation is=75 kHz Wideband FM system need large bandwidth, typically 15 times that of narrowband FM system Generation of FM using PM  x(t )dt Modulating Wave x(t) Integrator FM Wave Phase Modulator Carrier Oscillator Ec cos(2f ct) Advantages Amplitude of the frequency modulated wave remains unaffected Large decrease in noise, hence increase in S/N ratio Noise may reduce by increasing deviation Frequency allocation allows for a guard band which reduces adjacent channel interference Operate In Very high frequency (VHF) Disadvantages • FM has too much advantages besides it also has some disadvantages FM wave can’t cover large area Transmitting & receiving equipments for FM are complex & costly A much wider channel, typically 200 kHz, is needed for FM Applications: FM Radio FM radio uses a modulation index, m > 1, and this is called wideband FM As its name suggests the bandwidth is much larger than AM In national radio broadcasts using FM, the frequency deviation of the carrier  fc , is chosen to be 75kHz, and the information baseband is the high fidelity range 20Hz to 15kHz BW of FM radio=2(75k+15k) =180khz Television Sound: In terrestrial TV broadcasts, the video information is transmitted using AM However the sound information is transmitted using FM, in order to reduce possible interference between the video and sound signals In this case, the maximum deviation of the carrier,  fc , is chosen to be 50kHz, and the information baseband is again the high fidelity range 20Hz to 15kHz Therefore the bandwidth required for TV Sound is: BW Of TV Sound=2(50k+15k) =130khz Satellite TV Some satellite TV transmissions broadcast an analogue video signal using FM This helps to obtain an acceptable signal at the receiving station In this case, the maximum deviation of the carrier  fc , is chosen to be about 10 MHz, with a video baseband of around 5MHz Therefore the bandwidth required for Satellite TV is: BW of satellite TV =2(10+5) =30Mhz