I found this vi, which seemed to magically do the trick for me, so i attached it to the block diagram and added some indicators. It is possible to modulate information onto a wave via its frequency, amplitude, or phase, but all of these lead to a frequenc. Because the power spectrum loses phase information, you might want to use the fast fourier transform fft to view both the frequency and the phase information of a signal. Fourier transforms, page 2 in general, we do not know the period of the signal ahead of time, and the sampling may stop at a different phase in the signal than where sampling started.
Labview will be explored using some simple signals. Because the power spectrum loses phase information, you might want to use the fast fourier transform fft to view. National instruments believes that the information in this manual is accurate. Notice that the sine wave will move up and down as the dc is varied, its mean value equalling the dc value. Signal processing and analysing big mass data using labview. Computing the amplitude and phase spectrums labview 2018. Pam was added as an interpreter function in spectrum lab.
Im trying to plot a phase spectrum of sine wave with matlab. Then, students will use labview to program an am demodulator and use. In effect, modulation converts ft to a bandpass form, in the neighborhood of the center frequency f c. Pdf lab manual, labview code instructor resources labview code solutions. Thus to shift the phase of any harmonic by up to one cycle, one adds or subtracts any number between 0 and 360 degrees to its original value. This tutorial will take approximately 45 minutes and is designed for labview users of any level.
The code does three main jobs for calculation amplitude and phase spectra. The fundamentals of fftbased signal analysis and measurement. We start with the visual world, which varies with space, time, and wavelength, and has an amplitude spectrum roughly proportional to 1 f, where f is the spatial frequency of luminance variation. However, i then found out that the input to the vi must be real, so i cant use it. Overmodulated am signals and its requirement for coherent detection are. Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process. A labviewbased analog modulation tool for virtual and real experimentation article pdf available in ieee antennas and propagation magazine 546. Labview tutorial on spectral analysis national instruments. You will need to have read this manual before going through the lab slides. Look at this matlab function, it can calculate phase spectrum as well as amplitude spectrum with a perfect accuracy. As magnitude spectrum seems to be good, the phase spectrum seems to be uncorrect, its like a noise.
Measuring frequency and amplitude of analog signal with labview. Phasing is a process that combines the real and imaginary numbers in their proper ratio more simply, an improperly phased spectrum contains a distorted baseline around each peak, high on one side and low on the other it may even go negative. The waveform graph is an indicator that accepts an array of data values and plots the entire array at once. The fast fourier transform fft and the power spectrum are powerful tools for analyzing and. As a general rule of thumb, the phase spectrum is more important than the amplitude spectrum in that, if the amplitude spectrum is perturbed but the phase spectrum remains. Set g so that the sinewave peaks just fall to zero. Labview actually uses the discrete fourier transform dft, which takes considerably longer. Oqpsk o set quadrature phase shift keying oqpsk is a arianvt of phase shift keying modulation that uses four di erent aluevs of the phase to transmit. The word spectrum usually applies to just frequency. Phase noise noise sidebands phase noise page 33 penalty for sweeping too fast. What information is contained in the phase spectrum of a.
This manual describes analysis and mathematical concepts in labview. Chapter 3 explores the labview spectral processing tools such as dft and also. It requires that the amplitude of the dc a part of at is equal to the amplitude of the ac part a. Frequency modulation and demodulation with spectrum analysis. Complete amplitude and phase control of light using. Matlab amplitude and phase spectrum of a signal matlab. I took this example and wanted to modify the tx vi to show the amplitude and phase spectrum of the complex signal at the very end my modifications are uploaded as an attachment. All operations will be controlled via labview, using a code that builds off of. Converting a twosided power spectrum to a singlesided. Consider a sinusoidal carrier wave ct as fallow ct a ft cos2 cc. National instruments labview is an industryleading graphical software.
Fourier transforms, page 1 fourier transforms, dfts, and ffts. This program calculates amplitude and phase spectra of an input signal with acceptable accuracy especially in the calculation of phase spectrum. Amplitude modulation tutorial and am radio transmitter. Pdf a labviewbased analog modulation tool for virtual. Fast fourier transforms and power spectra in labview. What are the frequency spectrum, amplitude spectrum, and.
Also, it is not clear what question you are asking, or what help you need. The labview full and professional development systems include a basic fft power spectrum vi which can be used to create simple frequency domain plots from time domain data. Therefore there is also a phase spectrum for an organ pipe sound as well as an amplitude spectrum, the phase spectrum being a graph indicating how the phase of the waveform varies with frequency. Amplitude spectrum in quantity peak magnitude ffta n. User manual for more information about these boards. The magnitude in volts rms gives the rms voltage of each sinusoidal component of the timedomain signal. The power spectrum shows power as the mean squared amplitude at each frequency line but includes no phase information. Amplitude modulation this is lab 2 of 12 in the course by dr.
This example labview vi transmits and receives a digital bit stream in software using oqpsk. Though it is theoretically possible to transmit baseband signals or information without modulating. Plotting amplitude versus frequency data in labview. Below i attach code, i cant attach diagrams due to the lack of reputations. What information is contained in the phase spectrum of a signal. National instruments page 4 labview tutorial on spectral analysis definition. Ffts and the power spectrum are useful for measuring the frequency content of stationary or transient signals. We were told to make amplitude and phase spectrum of cosinus in matlab, but we dont have results nor materials from our teachers, so we have to study from many different materials and you can imagine what this is like. Labview digital signal processing and digital communications.
If the value of the modulation index is greater than 1, i. Put simply, iq data shows the changes in magnitude or amplitude and phase of a sine wave. Download this pdf document to find out how to access labview through your web browser and begin creating your vi in just minutes. Phase and amplitude monitoring functions in spectrum lab in 20100416, the phase and amplitude monitor short. Chapter 8 spectrum analysis introduction we have seen that the frequency response function tj of a system characterizes the amplitude and phase of the output signal relative to that of the input signal for purely harmonic. Modulation is a process by which characteristics of a highfrequency carrier signal are altered to convey information contained in a lowerfrequency message. The first major operations by the visual system are passive. I know what the amplitude spectrum is but i just cant make sense of the phase spectrum. The demodulation is performed by an envelope detector. Its purely a problem about programming with labview, and i cant find anything about that. Quadrature phaseshift keying qpsk using labview duration. Could someone show on this example how to plot amplitude and phase spectrum of any signal. Measuring frequency and amplitude of analog signal with.
Fft section later in this application note for an example this formula. Measurement of frequency, amplitude and phase myrio. First, this vi uses the following equation to compute the twosided amplitude spectrum. Generate plots of the amplitude and phase spectrum of a 30 hz sine. You obtain magnitude and phase information from complex data using the 1d. Phase of lo in a direction conversion system, the lo frequency is. This is different from the waveform chart, which scrolls data continuously, adding new data points to those already displayed. Measurement of frequency, amplitude and phase myrio by elgonza.
The amplitude and phase spectrum vi uses two steps to compute the singlesided, scaled amplitude spectrum. Tahmidur rahman on 7 feb 2018 plot an amplitude and a phase spectrum of the following signal st in matlab. Students will explore the mathematical theory behind amplitude modulation and use the analog discovery 2 to visualize the effects of amplitude modulation in the time and frequency domains. First of all, it extends the input signal to infinity. With the labview graphical programming environment, you can quickly and. This lab introduces students to communications theory with amplitude modulation and demodulation. There may be multiple instances incarnations of this function running simultaneously, if cpu power and sampling rate permit. Page 8 f1 f2 f swepttuned spectrum analyzer filter sweeps over a frequency range. Construct a labview vi that transmits and receives a digital bit stream in software using dpsk. Modulation changes a higher frequency carrier signal in. As the value of the modulation index increases, the carrier experiences a 180 o phase reversal, which causes additional sidebands and hence, the wave gets distorted. If amplitude and phase changes occur in an orderly, predetermined fashion, you can use these amplitude and phase changes to encode information upon a sine wave, a process known as modulation.
Phase spectrum of sine wave with matlab stack overflow. This tutorial is part of the national instruments measurement fundamentals series. Given that the amplitude spectrum and the phase spectrum, taken together, uniquely describe the time signature of a signal, it is pertinent to ask how these spectra, taken separately, contribute to the signal. If its a noisy signal then you probably want to use an fft to generate a power spectrum and get the amplitude and frequency from the largest peak in the spectrum. The usb6218 uses the daqmx driver and vis while the myrio is a rio based devices which uses labview realtime labview fpga so your code wont just move from one to the other without some modifications, mainly to the way you acquire the input. Run labview and open the transmitter and receiver vis that you created in the prelab. To view the phase spectrum in degrees, use the following equation. In the above example, we start sampling at t 0, and stop sampling at t 0. Set channel c to be a 31khz sine wave, amplitude 1v, phase 270deg, destination out1 at this point, you should have a 100 % amplitude modulated signal. This means that their ratio is unity at the output of the adder, which forces m to a magnitude of exactly unity. Tutorial on measurement of power spectra national instruments inc. Amplitude modulation am is one of the oldest of the modulation methods.
Subsampling a gsm signal assume that you are trying to sample. A sine wave can be mathematically described by a sine or cosine function with amplitude a c, frequency f c, and phase figure 2. In this video you will see amplitude modulation using different type of signals and channels. Figure 1 shows a schematic overview of the major structures of the early visual system and some of the functions they perform. I have a little problem with the subject theory of signal. How to plot phase and amplitude spectrum after doing. Labview creates virtual instruments vis, so, we can use the same vis for. Tutorial on measurement of power spectra physics 123253. Phase and amplitude monitoring functions in spectrum lab. When using the fft in labview and labwindowscvi, be aware that the speed of. This manual contains information about the labview sound and. I do not know what amplitude spectrum or phase spectrum would mean. Labview tutorial on spectral analysis with the labview graphical. The amplitude spectrum is not the real part of the fft, and the phase spectrum is not the imaginary part.436 619 1059 543 1218 874 933 234 1039 996 1266 977 1314 1434 288 40 1087 1108 1462 810 975 575 764 1213 1524 1423 294 1425 833 868 811 1137 425 597 916 757 466 753 79 84 1170 131 713 710