The proposed fm modulator and demodulator has been implemented and tested using xc2vp307ff896 fpga as a target device and can operate at a maximum frequency of. Throughout the world, the broadcast band falls within the vhf part of the radio spectrum. The generation of angle modulation may be based on a phase modulating principle 10 11 as sketched in fig. From its generation to modulation, the wave suffers minimal.
Its adjustment free modulation demodulation circuit significantly reduces the number of peripheral circuits required and can contribute to lower production costs. It is a detection technique of a received modulated signal. This experiment is in two parts, an fm modulator and an fm detector. In the second model, you will observe the frequency variations with respect to. The two modulators are identical except the reversal of sign of the modulating signal applied to them. In the first model, you are provided a fm structure that is very similar to the theoretical background of this experiment. Circuit of fm generation on breadboard fm demodulation circuit. Out of many methods of frequency generation, this tutorial covers one of the simplest and most efficient circuits. Fm receiver electronics circuit with full explanation. Armstrong fm transmitter indirect method of modulation, phase. As mentioned above, the capacitance cd of varactor diode d1 varies with the amount of its reverse bias voltage.
It should be noted, first that the output signal from the carrier oscillator is supplied to circuits. The modulation scheme could be amplitude modulation am, frequency modulation fm, phase modulation or some form of quadrature amplitude modulation qam, which is a combination of amplitude and phase modulation. Frequency modulation waveforms frequency demodulator, also called frequency discriminator, is a circuit, which converts instantaneous frequency variations to linear voltage changes. A known form of fm modulation circuit is shown in fig. Functions ask modulation and demodulation video signal fm modulation. My project in analog communications is consisting to have fm transmitter modulator that accepts a generated signal sin, cos and get me the modulated output as a graph. Pdf frequency modulation fm ransariya divyesh academia.
Pdf design and development of lowrange frequency modulated. It should be noted, first that the output signal from the carrier oscillator is supplied to circuits that perform the task of modulating the carrier signal. Let us consider the microphone to understand the sound signals and inside the mic, there is a presence. Phase modulation, and frequency modulation are both the modulation techniques analyzed in angle modulation. It is the process of deriving the original modulation signal from a modulated carrier wave.
There are two types of fm modulators direct and indirect. Two varactors, motorola mv209 are used to frequency modulate the oscillator. Frequency modulation fm is a process in which the carrier frequency is varied. The part of the armstrong fm transmitter armstrong phase modulator which is expressed in dotted lines describes the principle of operation of an armstrong phase modulator. Measure amplitude and frequency of the carrier signal. Its main advantage is that it is more resistant to additive noise than am. It has a very stable oscillator because you use lm7809 stabilizer which is a 9v stabilized power supply for t1 transistor and for frequency adjustment that can be achieved by using the 10k linear potentiometer. In the circuit, an fm signal with a 1khz modulating frequency, 5v20khz carrier signal, and a modulating index of 5 is fed to the input. Here we have adapted the same formula by first amplifying the audio signal, generating a carrier signal using an oscillating and then modulating the carrier signal with the amplified audio signal. In fm the baseband signal has to be integrated before it is applied to the modulator.
In this second experiment, we will examine the most common modulation scheme in daily life, namely, the frequency modulation, or fm. Describe fm demodulation circuit operation for the phaseshift and gatedbeam discriminators and the ratiodetector demodulator. Fm transmitter circuit working and its applications. Fm transmission is done by the process of audio pre amplification, modulation and then transmission. The la72912v is a fm modulation and demodulation singlechip. Department of electronics and communication engineering. The transmitting frequency of 88108 mhz is generated by adjusting vc1. This circuit assume a standard line level voltage for the input, so you can feed it with audio mixer, preamp, equalizer, or other various audio equipment. Any one of these capacitors could cause low output. In this video, i have explained frequency modulation fm by following outlines.
This tutorial explains circuit designing using a 555timer to generate a frequency modulated wave. Direct fm involves varying the frequency of the carrier directly by the modulating input. The circuitry is designed to operate in the vlf band at a carrier frequency of 100 khz. Here the basic building block is a voltage controlled oscillator. Amplitude modulators highlevel modulation produces the best type of am, but it requires an extremely high power modulator circuit. Seldom used but its circuit operation is basic to all tuned circuit frequency discriminators. To study frequency modulation and determine its modulation factor 4. Angle modulation changes the phase of a signal as well as its amplitude, where amplitude modulation leaves the phase unchanged. The tuned circuit formed by c 1 and l 1 performs the fm toam conversion and the peak detector formed by d 1, r 2, and c 2 extract the information from the am envelope. Its adjustment free modulationdemodulation circuit significantly. In fact, for 100% modulation, the power supplied by the modulator must be equal to onehalf the total class c amplifier input power. There are many types of circuits used in communication systems such as fm to am. The circuit is connected as per the circuit diagram shown in fig.
Simple fm transmitter circuit diagram and making it on breadboard. An advantage of frequency modulation is that it has a larger signaltonoise ratio and therefore rejects radio frequency interference better than an equal power amplitude modulation am signal. Pdf a new highperformance digital fm modulator and. Introduction in chapters 1 and 2 you studied how to apply intelligence modulation to an rfcarrier wave. The main reason for the improved fidelity is that fm detectors, when properly designed, are not sensitive to random amplitude variations. If any of these capacitors open or become leaky, the fm output may cease altogether. La72912v fm modulator and demodulator ic on semiconductor.
Stereo fm transmitter using ba1404 ic this is a stereo fm transmitter circuit using an ic from rohmm semiconductors named ba1404 which is a monolithic ic and has a builtin stereo modulator, fm modulator, rf amplifier circuitries. Without giving modulating signal observe the carrier signal at pin no. Frequency modulation is used in a radio broadcast in the 88108mhz vhf band. Along with 555 ic timers, the circuit is designed around a wien bridge oscillator circuit and a clamping circuit. Single transistor fm transmitter design in telecommunications, frequency modulation fm conveys information over a carrier wave by varying its frequency.
We designed the transmitter and receiver to oper ate at a frequency of 24. This method is used by design team 5 from ece480 to build a radar system with rf components that has a frequency of 2. Describe phase demodulation circuit operation for the peak, lowpass filter, and conversion detectors. The output frequency of approximately 100 mhz can be adjusted by changing the value of the. Indirect fm involves directly altering the phase of the carrier based on the input this is actually a form of direct phase modulation. The individual component of proposed fm modulator and demodulator has been optimized in such a way that the. Fm is commonly used at vhf radio frequencies for highfidelity broadcasts of music and speech.
Direct fm modulation frequency of the carrier changes according to mt. Armstrong fm transmitter indirect method of modulation. The modulating signal derived from the microphone is amplified and applied to the modulator. Sep 11, 2016 fm modulator circuit is a simple fm modulation circuit using ic 555, where the resulting modulated signal has a tenuous meeting depends on the signal frequency information. Fm modulator and demodulator ic overview the la72912v is a fm modulation and demodulation singlechip ic. The bottom diagram shows the resulting frequency modulated signal. Fm modulationdemodulation with pll general description package outline njw2307 is a fm modulation demodulation ic for audio signal in full duplex communication that operates from 3. For low fm signal outputs check capacitors c1, c2, c5, c6 and c7 with a capacitor checker. Instantaneous frequency the instantaneousfrequencyof cos. All of the parts listed below are provided in the analog starter kit, except for the 9v. The entire circuit of fm transmitter is divided into three major stages oscillator, modulator and amplifier. Pdf 4amplitude modulator and demodulator circuits appi t. In practice, this modulation will not be perfect, and there will be some amplitude modulation remaining. The resulting signal can be spelled out quite nice and stable so that the result will be more perfect.
What is fm, frequency modulation electronics notes. Input audio signal is reproduced by v4 voltage source. The c 3 is a blocking capacitor that keeps the dc bias out of the modulating signal circuits. That design wasnt meant for passing frequencies high enough to be able to pass an audio file, e. Using the audio frequencies to 3 khz and 5 khz sequentially. They operate on two tuned circuits at the center frequency and offer excellent linearity, both in amplitude and phase. How to demodulate an fm waveform all about circuits. Phase modulation is another type of angle modulation very similar to frequency modulation. Angle modulation provides the improved noise performance. Fm t for pm, the message mt does not need to be integrated. Locate the lm566 fm modulator circuit on module kl93004. The vco portion of an lm565 is used to create the fm waveform, and an lm565 phaselockedloop pll operates as the fm detector.
Fm transmitter and receiver project report pdf squarespace. Resistors in the reactance modulator circuit will be precision types with close tolerance. Keywords modulate exert a modifying or controlling influence frequency modulation the modulation. Direct fm modulation frequency of the carrier changes according to mt advantages of direct fm. This is very stable, harmonic free, long range fm transmitter circuit which can be used for fm frequencies between 88 and 108 mhz.
Apr 26, 2015 it uses a phase shift circuit it converts the instantaneous frequency deviation in an fm signal to phase shift and then detects the changes of phase cs results in 90 deg. We can use this circuit for fm wireless audio, microphone, other applications where a stable frequency modulated oscillator is needed. To study sampling and reconstruction of pulse amplitude modulation system 6. Keywords modulate exert a modifying or controlling influence frequency modulation the modulation of wave by variation of its frequency. Frequency modulation fm fm was invented and commercialized after am. Pdf pfrequency modulated fm signal transmitter is a small device that can. If the class c amplifier has an input power of w, the modulator must be. The fm modulator circuit frequency modulation is built with a motorola mc1648p oscillator. Project aim the aim of the project is to design am fm modulation using labview glanguage objective. This fm modulator can be operated between 76 to 108mhz.
The la72914v is a fm modulation and demodulation ic for audio signals. This method is called indirect fm in contrast to direct fm that is shown in fig. Reactance modulator circuit operation and troubleshooting. Locate the mc1648 fm modulator circuit on module kl93004. I got the idea for this circuit from one of my professors. Ive found this fm transmitter circuit 3 km rangetwo muppets1 and i am building that circuit on multisim, and i failed. Research article a new highperformance digital fm modulator. Some phase modulation and quadrature amplitude modulation formats have a higher spectral efficiency for data transmission than frequency shift keying, a form of frequency modulation. The entire circuit diagram and the image of the circuit wired in the bread board is shown in the following figure. Fm modulation and demodulation circuit multisim live. In addition to audio signal, it can also be used in data pulse. The ratio between carrierfrequency deviation in hertz and modulating frequency also in hertz. The proposed fm modulator and demodulator has been implemented and tested using xc2vp307ff896 fpga as a target device and can operate at a maximum frequency of 334.
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