Demodulate the signal and recover the original modulating waveform using two methods for. Quadrature demodulation can extract angle information that is relevant to both frequency modulation and phase modulation. Angle modulation changes the phase of a signal as well as its amplitude, where amplitude modulation leaves the phase unchanged. The main difference between amplitude modulation and frequency modulation is that, in amplitude modulation, the amplitude of the carrier wave is modified according to the data whereas, in frequency modulation, the frequency of. Frequency modulation consists of encoding information onto a carrier signal by varying the frequency of the carrier.
Frequency modulation is widely used on frequencies above 30 mhz, and it is particularly well known for its use for vhf fm broadcasting. Frequency modulation and phase modulation are the two complementary principal methods of angle modulation. The goal of this experiment is to become familiar with fm modulation and demodulation. Each channel sharing scheme a set of basis vectors. We shall focus more on frequency modulation in this course and less on phase modulation. It is also possible to change the frequency of a signal to give frequency modulation or fm. The fm modulation and demodulation process is identical in stereo and monaural processes. Fm modulation and demodulation will be presented and you will implement two types of demodulators, the frequency discriminator and the phaselocked loop. Radio transmission voice microphone electric signal, 20 hz 20 khz transmitter antenna. There are many types of modulation so there are many types of demodulators. Frequency modulation fm is the standard technique for highfidelity communications as is evident in the received signals of the fm band 88108 mhz vs. Frequency modulation is a form of modulation, which represents information as variations in the instantaneous frequency of a carrier wave.
Build simple fm demodulator by using frequency discriminator. Although there could be more than two frequencies involved in an fsk. In particular, we discuss amplitude and frequency modulation. It is relatively difficult to tune, as tuned circuit must be tuned to different frequency than carrier frequency. What is fm, frequency modulation electronics notes. Once a signal has been modulated, information is retrieved through a demodulation process. The frequency modulated signal is therefore described in the time domain by.
In singlechannel efield sensing, the carrier we transmit is m, the sensed value is a, and the noise is n vectors. While changing the amplitude of a radio signal is the most obvious method to modulate it, it is by no means the only way. The frequency modulator and demodulator structures are as explained below. Oct 05, 2015 amplitude modulation and frequency modulation are both methods of modifying a carrier signal in order to transmit data. That could be the amplitude, phase, or frequency, which result in amplitude modulation am, phase modulation pm, or frequency modulation fm. The following plot shows the waveform created by the sffm voltage source. Principles of communication modulation tutorialspoint.
Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a. Choose the amplitude of the message such that the maximum frequency deviation is 30 khz. To implement the simulink models for fm including a basic sinusoid and a multimedia file music to analyze each signal in time and frequency domains using time scope and spectrum analyzer. Introduction in chapters 1 and 2 you studied how to apply intelligence modulation to an rfcarrier wave. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. These methods contrast with amplitude modulation, in which the amplitude of the carrier wave varies, while the frequency and phase remain constant. Fm modulated signal st is a nonlinear function of the modulating signal mt, thus it is known as nonlinear modulation process. Its main advantage is that it is more resistant to additive noise than am. Describe fm demodulation circuit operation for the phaseshift and. It reacts to all amplitude changes needs a limiter. Modulation allows us to transmit multiple signals in the same medium i. It is the extent of modulation denoted in percentage, and is denoted by m. Part i experiments involving linear modulation and demodulation. Use modulation to transfer information to a higher frequency.
Fm modulation and demodulation will be presented and you will implement two types of demodulators, the frequency. One approach to reduce this interference, known as frequency division multiplexing, allocates different carrier frequencies to different users or. Frequency modulation frequency modulation is the process by which frequency of the carrier signal ct changes with respect to the modulating signal mt. Preparation generation as its name suggests, a frequency shift keyed transmitter has its frequency shifted by the message. Request pdf digital phase modulation and demodulation digital phase modulation is a class of power and bandwidthefficient modulations widely used in telecommunications.
Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude of the modulating signal i. For such a signal, to travel longer distances, its strength has to be increased by modulating with a high frequency. The concepts of amplitude modulation, modulation and demodulation, along with their. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. Frequency modulation is a technique or a process of encoding information on a particular signal analogue or digital by varying the carrier wave frequency in accordance with the frequency of the modulating signal.
In modulation, one characteristic of a signal generally a sinusoidal wave known as the carrier is changed based on the information signal that we wish to transmit modulating signal. Modulation is the process of changing the parameters of the carrier signal, in accordance with the instantaneous values of the modulating signal. Build simple envelope detector for fm demodulation. A carrier wave is purely made up of constant frequency, slightly similar to a sine wave. The frequency of a radiofrequency channel can be explained best as the frequency of a carrier wave. As with any form of modulation, it is necessary to be able to successfully demodulate it and recover the original signal. In the first model, you are provided a fm structure that is very similar to the theoretical background of this experiment. Phase modulation is another type of angle modulation very similar to frequency modulation. Carsons rule and woodwards theorem use a 250 hz sine wave, square wave, and triangle wave to frequency modulate the hp3314a. The first demodulation technique that well look at begins with a highpass filter. It is in the field of telecommunications and signal processing, that this kind of technique is mostly used. Once the signal has been received, filtered and amplified, it is necessary to recover the original modulation from the carrier.
The most basic frequency demodulator consists of a frequency discriminator, which is a differentiator followed by an envelope detector, as shown in figure 3. Carrier modulation allows the transmission of modulating frequencies without the use of transmission wire as a medium. Frequency discrimination slope detector major limitations. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation.
Frequency modulation and demodulation last modified. Difference between amplitude modulation and frequency modulation. It is inefficient, as it is linear in very limited frequency range. The fm demodulator may be called a variety of names including fm demodulator, fm detector or an fm discriminator. The baseband signals are incompatible for direct transmission. Fm signals have the same peak frequency deviation, then when mt is a sinusoidal signal set such that the pm and note. The first step in the receiver will be demodulation of the received signal where the. Teach the basics of frequency modulation and demodulation. Amplitude modulated am signal and four demodulation methods for fre quency modulated fm signal. However if st is sinusoidal, then the instantaneous frequency deviation of the anglemodulated signal is. Quadrature frequency and phase demodulation radio frequency. It does not carry much information that we can relate to data or speech. In theory an fm signal contains an infinite number of side frequencies so that the band width required to transmit such a.
Radio waves can carry audio, video, and digital information over great distances by using changes in a carrier waves amplitude, frequency, or phase to represent the information being transmitted. Fm is in contrast with amplitude modulation where amplitude of the carrier waves is modulated with frequency remaining unchanged and constant. Chapter 8 frequency modulationfm fm was invented and commercialized after am. Fm is considered an analog form of modulation because the baseband signal is typically an analog waveform without discrete, digital values. Instantaneous frequency the instantaneousfrequencyof cos. Frequency modulation fm is the encoding of the information in a carrier wave by varying the instantaneous frequency of the wave. Frequency modulation definition, applications, advantages. To recover the message signal from the fm signal, frequency demodulation must be performed. To understand the theoretical foundations for angle modulation as well as frequency modulation fm and demodulation.
Frequency division multiplexing, fdma amplitude modulation and demodulation. The demodulation of a fm signal requires a circuit that yields an output voltage. Jun 05, 2015 physics course of 12th class modulation frequency modulation fm by ashish arora ga. Fm modulation and demodulation ee labs home university of. Advantages and disadvantages of frequency modulation. Fm demodulation is a key process in the reception of a frequency modulated signal. From 3 we can find that the frequency of frequency modulated signal occurs frequency deviation from the center frequency of the carrier when the intelligence. For a perfect modulation, the value of modulation index should be 1, which means the modulation depth should be 100%. A demodulator is an electronic circuit or computer program in a softwaredefined radio that is used to recover the information content from the modulated carrier wave. One of the minor disadvantages of frequency modulation is that the demodulator is. Describe phase demodulation circuit operation for the peak, lowpass filter, and conversion detectors. Digital phase modulation and demodulation request pdf. Demodulation is extracting the original informationbearing signal from a carrier wave. Frequency modulation fm is a form of modulation in which changes in the carrier wave frequency correspond directly to changes in the baseband signal.
It is this process that is called demodulation or detection. Pm and digital modulation s p where 2 is the pkpk phase change in one symbol duration, t for digital signals the modulation index. Radio systems can use a digital signal processor in conjunction with an analogtodigital converter to apply mathematical analysis to iq waveforms. In analog applications, the carrier frequency is varied in direct proportion to changes in the amplitude of an input signal.