Bandpass modulation and demodulation techniques communication systems, dept. Some parameter of the carrier amplitude, frequency, phase is. In analog applications, the carrier frequency is varied in direct proportion to changes in the amplitude of an input signal. Pulsecode modulation pcm is a method used to digitally represent sampled analog signals.
The demodulation demonstration is set up by configuring the board for 100% modulation and connecting one channel of the scope to the audio waveform at tp1 and the other channel the output. Amplitudefrequency modulation communication system. The code of qpsk modulation and demodulation technique has been developed according to the theory. Frequency modulation and frequency demodulation experiment tutorial by mr. Hi, im a beginner in matlab and im just wondering whether the modulation constant. It reacts to all amplitude changes needs a limiter. The signal flow below shows how the bilif is connected and replaces the internal modulation and demodulation hardware. We begin our discussion of digital modulation by starting with the three basic. A square wave with carrier frequency is multiplied with the message signal. Review pulse train bandwidth s ingle pulse of duration. Amplitude and frequencyphase modulation i always had di culties in understanding frequency modulation fm and its frequency spectrum. The proposed demodulator is an alldigital implementation of a fm. This modulation method is, therefore, referred to as fm or frequency modulation. I am trying to frequency demodulate a frequency modulated ecg signal done by a hardware circuit.
In singlechannel efield sensing, the carrier we transmit is m, the sensed value is a, and the noise is n vectors. Teach the basics of frequency modulation and demodulation duration. The continuous analog signal st is a baseband signal with the information content. It is relatively difficult to tune, as tuned circuit must be tuned to different frequency than carrier frequency. The underlying theme of this lab is angle modulation, in particular frequency modulation fm. Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process. Amplitude and frequency phase modulation i always had di culties in understanding frequency modulation fm and its frequency spectrum.
For example, an am radio system transmits electromagnetic waves with. To recover onoff keyed information, we need a method of detecting the presence or absence of rf oscillations. Orthogonal frequency division multiplexing ofdm is a multicarrier modulation technique which is very much popular in new wireless networks of ieee standard, digital television, audio. All digital fm demodulator kartik nair vtechworks virginia tech. Real and complex modulation tipl 4708 presented by matt guibord prepared by matt guibord 1. In a pcm stream, the amplitude of the analog signal is sampled regularly at uniform intervals, and each sample is quantized to the nearest value within a range of digital steps. As with any form of modulation, it is necessary to be able to successfully demodulate it and recover the original signal. Pdf an analog method to modulate and demodulate signals is presented.
Because of the low cost of the parts necessary to implement am transmission and the simplicity of the underlying technology, using amplitude modulations is a cheap and effective way to perform many tasks that require wireless communication. Am modulation at a carrier frequency, kc, specified by the student. In any radio that is designed to receive frequency modulated signals there is some form of fm demodulator or detector. The input modulated waveform, original audio waveform, demodulator output, and. Midinfrared wavelength and frequency modulation spectroscopy. It is still in use today in a variety of systems, including, of course, am broadcast radio. This work discusses the demodulation scheme for one of the most. The theoretical description of qpsk modulation and demodulation are available in the book of communication system by simon haykin. The second is to investigate classical analog amplitude modulation and the envelope detector. Frequency modulation, single tone frequency modulation, spectrum analysis of sinusoidal fm wave, narrow band fm, wide band fm, constant average power. However if st is sinusoidal, then the instantaneous frequency deviation of the anglemodulated signal is. Amplitude modulation am is an analog modulation scheme where the amplitude a of.
Fsk frequency shift keying d1 61 conceptually, and in fact, the transmitter could consist of two oscillators on frequencies f1 and f2, with only one being connected to the output at any one time. High frequency waveforms require smaller antennae for reception, efficiently use available bandwidth, and are flexible enough to carry different types of data. This is called the process of modulationand demodulation remember the radio spectrum. Matlab code for qpsk modulation and demodulation file. The sampling frequency is obtained by using the counter to divided the 2048 khz square wave signal by 256. The goal of this experiment is to become familiar with fm modulation and demodulation. Build simple fm demodulator by using frequency discriminator. F 2 the modulation in psoc 3 and psoc 5lp is achieved using the mixer component in up mixer mode. In telecommunications and signal processing, frequency modulation fm is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave in analog frequency modulation, such as fm radio broadcasting of an audio signal representing voice or music, the instantaneous frequency deviation, the difference between the frequency of the carrier and its center. Frequency modulation of the diode laser was transferred to the opos. Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude of the modulating signal i.
The demodulation is performed by an envelope detector. Frequency modulation and demodulation file exchange. Microringbased modulation and demodulation of dpsk signal lin zhang1, jengyuan yang 1, muping song 1,2, yunchu li, bo zhang 1, raymond g. The fm demodulator may be called a variety of names including fm demodulator, fm detector or an fm discriminator. Once a signal has been modulated, information is retrieved through a demodulation process. Usrp 2901 based fm transceiver with large file capabilities in. The focus of this lab is to familiarize the student with the modulation and demodulation of an am signal. There are several ways of demodulation depending on how parameters of the baseband signal such as amplitude, frequency or phase are transmitted in the carrier signal. If not, what is the default depth of modulation for am here.
Fm demodulation, stages and types of demodulators prezi duration. Frequency modulation is the instantaneous change of the carrier frequency, fc by the. During the demodulation lesson, the modulated carrier is fed into a demodulator circuit. Frequency modulation consists of encoding information onto a carrier signal by varying the frequency of the carrier. Modulation is the process of influencing data information on the carrier, while demodulation is the recovery of original information at the distant end from the carrier. Rc audio generator, oscilloscope, and spectrum analyzer demonstrations with speech and radio. Demodulation is the reverse process of modulation, which is used to get back. Upon completion of the experiment, the student will. Pdf simulation of analog modulation and demodulation. To recover the message signal from the fm signal, frequency demodulation.
I always had difficulties in understanding frequency modulation fm and its frequency spectrum. Since the frequency change of a sinusoid in time results in alternation of phase in time, fm may also be referred to as phase modulation, or pm, as well. Phase and amplitude modulation a phase and amplitude modulated carrier signal can be. Fm demodulator circuits are found in any receiver that uses fm. The lif port modification does not alter the standalone capabilities of the transceiver, but when it is connected to the computer, it creates a powerful ifsdr transceiver. Continuouswave demodulation continuouswave cw modulation consists of onoff keying of a carrier wave.
There are a variety of modulation schemes available for both analog and digital modulation. Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a. A modem is an equipment that performs both modulation and demodulation. Even for the pure tone modulation, the fm spectrum consists of an in nite number of sidebands. One of the minor disadvantages of frequency modulation is that the demodulator is.
In an earlier semester project, four fm demodulation algo. Frequency modulation is a form of modulation, which represents information as variations in the instantaneous frequency of a carrier wave. Demonstration with professor sandy hill from the university of massachusetts at amherst. Frequency and phase modulation sharlene katz james flynn overview history why fm. Ece 4670 spring 2014 lab 5 frequency modulation, demodulation. Is there a way i can vary it, say, to 100% modulation depth.
I ntroduction an amplitude modulated signal is composed of both low frequency and high frequency components. Wave fundamentals and modulation demonstration board. Overmodulated am signals and its requirement for coherent detection are also considered. The discussion then moves to binary phase shift keying bpsk and shows how this simpler format is modeled using the generic quadrature modulation models.
The instructor would begin the demodulation demonstration by providing some background material on the concept of demodulation. Microringbased modulation and demodulation of dpsk signal. It is inefficient, as it is linear in very limited frequency range. Phase modulation and demodulation file exchange matlab. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. That could be the amplitude, phase, or frequency, which result in amplitude modulation am, phase modulation pm, or frequency modulation fm. Amplitude and frequencyphase modulation zurich instruments. The modulator outputs two files, the first with the modulated signal exactly n real elements long and the other a special trinary signal where 1 indicates time location of a 1 bit and 1 indicates the location of a 0 bit.
Amplitude modulation am radio is a commonplace technology today, and is standard in any type of commercial stereo device. What is fm, frequency modulation electronics notes. Each channel sharing scheme a set of basis vectors. Frequency discrimination slope detector major limitations. This is generally accomplished using a high frequency carrier sinusoid and a lower frequency modulation waveform such as an audio signal from microphone. The details of both modulation and demodulation are investigated. The focus of this lab is to familiarize the student with the modulation and demodulation of. 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. Build simple envelope detector for fm demodulation. For example, for a signal modulated with a linear modulation like am amplitude modulation, we can use a synchronous detector. The cw demodulator detects the presence of rf oscillations and converts them into a recognizable form. Square low fet amplitude modulator fet is nonlinear element. A similar approach is then taken for developing models for multiple phase shift keying mpsk, minimum shift keying msk, and frequency shift.
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