Frequency modulation and its application
Download as PPTX, PDF42 likes46,871 views
This document discusses frequency modulation (FM) including its definition, modulation index, spectrum characteristics, types of FM modulation, generation of FM using phase modulation, advantages and disadvantages compared to other modulation techniques, and applications of FM such as in radio broadcasting, television sound, and satellite television. FM provides noise immunity and allows adjusting the noise level by changing the frequency deviation. It is widely used for radio but requires more complex transmission and reception equipment than other modulation methods.
Frequency modulation and its application
- 1. Frequency Modulation and Application Submitted by: Darshil Shah (IU1241090051)
- 2. Content 1. Flow diagram 2. What is frequency modulation? 3. Frequency modulation index 4. Significant-sidebands Spectrum 5. Types of FM 6. Generation of FM using PM 7. Advantages and disadvantages 8. Comparison with FM and PM 9. Applications
- 3. Modulation Pulse Wave Modulation Amplitude Modulation Continuous Wave Modulation Linear Modulation Non-Linear Modulation Frequency Modulation Phase Modulation
- 4. 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 nonlinear-modulation?
- 6. 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,
- 7. 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).
- 8. 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.
- 9. 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.
- 10. Generation of FM using PM Modulating Wave x(t) FM Wave Integrator Phase Modulator Carrier Oscillator dtt x ) ( Eccos(2fct)
- 11. Advantages 1. Amplitude of the frequency modulated wave remains unaffected. 2. Large decrease in noise, hence increase in S/N 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).
- 12. 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.
- 13. Comparison of FM with PM Sr. No. FM PM 1 Frequency deviation is proportional to modulating voltage Phase deviation is proportional to the modulating voltage 2 Noise immunity is better than AM and PM Noise immunity is better than AM but worse than FM 3 SNR is better than PM SNR is worse than FM 4 FM is widely used for radio broadcasting PM is only used in some mobile systems 5 It is possible to receive FM on PM receive It is possible to receive PM on FM receive 6 Modulation index is proportional to modulating voltage as well as the modulating frequency . Modulation index is proportional to modulating voltage
- 14. Comparison of FM and AM Sr. No. FM AM 1 FM receivers are immune to noise AM receivers are not immune to noise 2 It is possible to decrease noise by increasing deviation This feature is absent in AM 3 Bandwidth is higher and depends on modulation index Bandwidth is lower compared to AM but independent of modulation index 4 FM transmission and reception equipment are more complex FM transmission and reception equipment are less complex 5 All transmitted power is useful Carrier power and one sideband power is useless
- 15. 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:
- 16. 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
- 17. References • http://www.silabs.com/Marcom%20Documents/Resources/FMTutorial.pdf • http://en.wikibooks.org/wiki/Communication_Systems/Frequency_Modulati on • http://www.radio-electronics.com/info/rf-technology-design/fm-frequency-modulation/ spectrum-bandwidth-sidebands.php • http://searchnetworking.techtarget.com/definition/frequency-modulation • https://www.youtube.com/watch?v=SmW4z76KgNQ • https://www.standrews.ac.uk/~www_pa/Scots_Guide/RadCom/part12/page 1.html • Analog and digital communication system by Sanjay Sharma. • Modern digital and analog communication systems by B.P. Lathi
Editor's Notes
- #12: Because frequency will be changed according to the baseband signal Because FM receiver may be filtered with amplitude limiters to remove the amplitude variation caused by noise this makes FM reception a good deal to immune noise. In AM this feature is absent 98.3 channel’s some interference will be get in both adjacent channels compare with FM in AM it will be very high 88Mhz to 108Mhz
- #14: Delta f=k e & delta f= k e Refer advantages Refer advantages Application Vice-versa M=k e /f & M=k e
- #15: 1 to 4 Advantages