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Fm Transmitter and receiver
- 1. FM – Transmitters And Receivers By Nur Mohammad All Nasser
- 2. Introduction The FM transmitters and receivers are those devices which is used for sending and receiving FM signal. The transmitters are those devices which is used to send frequency modulated wave through a band and the receivers are the devices which received modulated signal then after demodulation it gives us the original signal.
- 4. What is Frequency Modulation? When the audio signal is modulated onto the radio frequency carrier, the new radio frequency signal moves up and down in frequency. The amount by which the signal moves up and down is important. It is known as the deviation and is normally quoted as the number of kilohertz deviation. As an example the signal may have a deviation of plus and minus 3 kHz, i.e. ±3 kHz. In this case the carrier is made to move up and down by 3 kHz. • Broadcast stations in the VHF portion of the frequency spectrum between 88.5 and 108 MHz use large values of deviation, typically ±75 kHz. This is known as wide-band FM (WBFM). These signals are capable of supporting high quality transmissions, but occupy a large amount of bandwidth. Usually 200 kHz is allowed for each wide-band FM transmission. For communications purposes less bandwidth is used. Narrow band FM (NBFM) often uses deviation figures of around ±3 kHz. • It is narrow band FM that is typically used for two-way radio communication applications. Having a narrower band it is not able to provide the high quality of the wideband transmissions, but this is not needed for applications such as mobile radio communication.
- 5. Why we do use FM communication? • Efficiency • The efficiency of a signal is the power in the side-bands as a fraction of the total. In FM signals, because of the considerable side-bands produced, the efficiency is generally high. Recall that conventional AM is limited to about 33 % efficiency to prevent distortion in the receiver when the modulation index was greater than 1. FM has no analogous problem. • The side-band structure is fairly complicated, but it is safe to say that the efficiency is generally improved by making the modulation index larger (as it should be). But if you make the modulation index larger, so make the bandwidth larger (unlike AM) which has its disadvantages. As is typical in engineering, a compromise between efficiency and performance is struck. The modulation index is normally limited to a value between 1 and 5, depending on the application.
- 6. • Noise • FM systems are far better at rejecting noise than AM systems. Noise generally is spread uniformly across the spectrum (the so-called white noise, meaning wide spectrum). The amplitude of the noise varies randomly at these frequencies. The change in amplitude can actually modulate the signal and be picked up in the AM system. As a result, AM systems are very sensitive to random noise. An example might be ignition system noise in your car. Special filters need to be installed to keep the interference out of your car radio. • FM systems are inherently immune to random noise. In order for the noise to interfere, it would have to modulate the frequency somehow. But the noise is distributed uniformly in frequency and varies mostly in amplitude. As a result, there is virtually no interference picked up in the FM receiver. FM is sometimes called "static free, " referring to its superior immunity to random noise.
- 7. Different Type Of FM • NARROW BAND F.M. We know that the bandwidth of an FM signal depends upon the frequency Deviation (∆𝜔 = 𝑘𝑓. 𝑥(𝑡).if frequency deviation is low it means 𝑘𝑓 is low then bandwidth will be narrow then narrow band FM is formed. • WIDEBAND FM If frequency deviation (∆𝜔 = 𝑘𝑓. 𝑥(𝑡) is high , it means frequency sensitivity 𝑘𝑓 is high result as bandwidth will be wide hence wide band is formed
- 9. . • Crystal oscillator – Crystal oscillator generates the stable carrier signal. • Phase modulator - The phase modulator modulates the carrier signal and the massage signal in the low power range to generate a narrowband FM. Frequency multiplier - The frequency multiplier is used to increase the frequency deviation and carrier signal frequency to a desired level. Power Amplifier - The power amplifier gives the required power level to the signal which passes through the antenna. Antenna - Antenna is a device which is used for sending and receiving the information.
- 10. FM Receiver
- 11. • RF tuned amplifier - These amplifiers are used for impedance matching to minimise noise level. Mixer - These oscillator circuits are take any form to mix up the frequency modulated signal for performing the operation in such circuit central frequency are change but deviation are constant. Intermediate frequency amplifier - The IF amplifier provides most of the gain and bandwidth requirement of the receiver. Limiters - Limiters are those circuit which allows the certain frequency range to pass out and block the other signals.
- 12. . Discriminator - The discriminator change FM into AM. A simple diode detection then recover the intelligence contained in the envelop of the AM waveform. De-emphasis - The artificial boosting given to the higher modulating frequencies in the process of pre-emphasis is nullified or compensated at the receiver by the process of De emphasis. Vol & tone controller - In this circuit it control the efficiency of audio signal. The signal whose efficiency is more then audible range are neglected in this circuit. Power amplifier – The power amplifier gives the required power level to the signal which passes through the loudspeaker.
- 13. ADVANTAGES OF FM OVER AM Noise reduction Improved system fidelity More efficient use of power DISADVANTAGES OF FM OVER AM Increased band width Use of more complex circuit
- 14. APPLICATIONS Radio broadcasting Two way mobile radio Microwave communication TV sound transmission Cellular radio communication Satellite communication
- 15. The equipment we would use and estimsted cost : Name Quantity Unit Price Amount (Taka) 1. 9V Battery 3 20 60 2. 494Transistor emitter 1 10 10 3. 100UF16V 1 5 5 4. 22k 5 1 5 5. 4ohm speaker 1 50 50 6. Wire 1 40 40 7. Ic 386 1 20 20 8. 10kv 1 15 15 9. 100f capacitor 1 2 2 10. Battery clip 2 5 10 11. Project board 1 65 65 12. Ri5 200 .15 30 13. 2N3904 2 5 10 14. 33pif 5 1 5 15. Microphone 1 10 10 16. 22pf 1 2 2 Total =537
- 16. . • These are the estimated cost . Some equipment we will destroyed when will start eperiment . So , exact cost we can tell after completing the eperiment .
- 17. Thank You