FM Transmitter

FM Transmitter Transmitter

National University of Computer and Emerging Sciences

21 April 2011

Presented to: Engineer Fahad Raees Submitted by: Waseem Shah

Table of Contents:

1.

Objective

2. Definition 3. Theory 4. Apparatus 5. Procedure 6. Data and Calculations 7. Results and Conclusions

Objective:

The objective of our project is to design an FM transmitter that transmits signals using frequency modulation.

Definition: Modulation: a modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal , with respect to a modulating signal (which (which typically contains information to be transmitted). Frequency modulation (FM): It is a technique which conveys information over a carrier wave by v arying its instantaneous frequency.

Carr ier  Wave: a carr ier  wave, or ca or carr ier  is a waveform (usually sinusoidal) sinusoidal) that is i s modulated (modified) (modified) with an input signal for the purpose of conveying information. This carrier wave is usually of much higher frequency than the input signal.

Theor y: y: Frequency modulation is the instantaneous changing of the carrier frequency fC proportional to the information modulating signal. The amplitude of the information signal, ES which changes with time, t will change the carrier frequency while the carrier amplitude remain fixed. The carrier frequency varies linearly with the amplitude of modulating signal. The higher the amplitude of modulating signal the bigger frequency difference produced. FM signal can be represented by equation: FM = EC cos ( wCt +  m(t) m (t) dt ) Frequency modulation process is carried out by an FM modulator as illustrated below:

Information signal :

m(t) = E m cos w m t  FM MODULATOR  FM signal : EC cos ( wCt +  m(t) dt ) 

Carrier Signal EC cos wCt

Apparatus: y

Capacitors

y

Resistors

y

Transistor

y

Microphone

y

Inductor

y

Breadboard

y

9v-Battery

y

Antenna

Procedure:

A condenser microphone is used to pickup the sound, converts it into electrical signals and they are fed to the base of a transistor which performs the amplification as well as modulation. The output of  the transistor is fed to a capacitor which is connected to the psoitive terminal of a 9v battery. The LC circuit which comprises of and inductor and capacitor determines the frequency signal, and can be varied by varying the flow of charge towards a capacitor of LC circuit. Another, capacitor is used to couple the singal with the antenna which then transmits the signal into air as an RF(Radio Frequency) signal.

Data and Calculations: The data are the values of the resistance and the capacitance in order to calculate the centre frequency of the signal. Its formula is given below:

Fc=1/2RC R = _________ C=__________ Fc=_________

Results and Conclusions: The result is that the voice was heard at the desired frequency over which it was sent.