Frequency Modulation and Application

Submitted by:Darshil Shah

(IU1241090051)

Content

1. Flow diagram2. What is frequency modulation?3. Frequency modulation index4. Significant-sidebands Spectrum 5. Types of FM6. Generation of FM using PM7. Advantages and disadvantages8. Comparison with FM and PM9. Applications

Modulation

Amplitude Modulation

Pulse WaveModulation

Continuous WaveModulation

Linear Modulation

Non-Linear Modulation

FrequencyModulation

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 nonlinear-modulation?

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 DeviationModulating 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 FMNarrow 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 FMWide 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 Wavedttx )(

)2cos( fctEc

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).

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.

Comparison of FM with PMSr.

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

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 andreception equipment are less complex

5 All transmitted power is useful Carrier power and one sideband power is useless

FM RadioFM 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

References • http://www.silabs.com/Marcom%20Documents/Resources/FMTutorial.pdf

• http://en.wikibooks.org/wiki/Communication_Systems/Frequency_Modulation

• 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/page1.html

• Analog and digital communication system by Sanjay Sharma.

• Modern digital and analog communication systems by B.P. Lathi