Spectrum analyzer using FFT via LabVIEW
Works on virtual laboratories
Fatima Moumtadi Ph. D. Department of Electronic, School of Engineering
UNAM
Mexico City, Mexico
fatima@
Julio Delgado Ph. D
School of Engineering
Universidad Anahuac柳州的
旅游景点有哪些
Mexico City, Mexico吉林周边游玩景点一日游
caldelherelher@gmail
Felix Ruiz Mendoza, BE Department of Electronic, School of Engineering
UNAM
Mexico City, Mexico
chrisu2dell@yahoo
Roberto Tovar Medina, MEng Department of Electronic, School of Engineering
UNAM
Mexico City, Mexico
rtovar_fi@
Abstract— This paper belongs to a set of efforts aimed to improve the education of engineering in electronic and telecommunications, based on virtual equipment. It stand on a previous work called Networking Model for a Virtual Radio Frequency Laboratory (NMFLV) [1]. This proposal addresses with a specific topic in radio frequency. Plenty of analysis is performed in the frequency domain due t无锡太湖
鼋头渚风景区
o limits for time analysis. In order to understand this phenomenon the analyzer uses Fast Fourier Transform, its efficiency in the amount of mathematical operations, FFT is limited only by the number of samples. As it was mentioned our goal is boost the learning process, using IT infrastructure along with electronic prototypes, besides encourage students to use their pace in laboratory activities. The work introduced is performed via NMFLV system;
it was designed a spectrum analyzer for undergraduate students and postgraduate students.
Keywords-component: Education, Instrumentation, OPAMP.
I.I NTRODUCTION
Radio Frequency systems studies and experiments are mainly based on the frequency domain; time domain analysis is not appropriated due to limits in the mathematics that are needed to resolve equations. However if the signal is transformed to frequency domain trough Fourier transform, in this domain, the equations reduces its complexity to solve. Besides this when the signal are processed for being manipulated it is necessary to going further, the more efficiently computation the more convenience solution, this is why Fast Fourier Transform is used in almost every signal area.
The problem to be addressed when we acquired data is aliasing, it is possible to fix if the signal is sampled at double frequency rate that the highest component has and adding a low pass filter, actually it is a 2 kHz low pass amplifier operational filter.
For this purpose it was used a virtual instrumentation developed called NMFVL, this system allows the students to visualize electronic equipment parameters into an agile, precise and reliable form.
Plenty of the students that work in the development of a virtual interface have better practices than the traditional laboratory solutions [6], where usually the acquisition and processing sets are separated. Along the technical part, students get benefits from interdisciplinary working environment, they could improve their social skills that are not addressed at engineering schools, due to the work in virtual laboratories, students requires knowledge integration of: structured programming, G language, electrical and electronic design, radio communications, signal processing and information, among others. This experience contributes with his background when they are on the path of work.
II.P ROJECT DESCRIPTION
As it was above mentioned; the model developed includes
a low cost PC (Compaq Dual Core E2140) connected to a LAN, a set of data acquisition electronic cards (PCI 5152) used, a digital Multimeter (NI USB-4065 USB DMM) and also
it is possible to use a 40 MHz functions generator NI PCI-5406, [5].
The electronic circuit part includes a basic inverter with operational amplifier (LM741). The virtual laboratory was planned to designed, integrated and implemented within students scope, they could measure, visualize and understand the behavior of phenomenon as fast, as they can, it point out the awareness of their knowledge.
III. P ROBLEM TO SOLVE
In order to perform low cost experiment, public universities take advantage of platforms that could manage a large amount of students in a short period. LabVIEW is a perfect tool that is easy to use; taking advantage of this fact the laboratory uses NMFLV.
For this paper it was used a spectrum analyzer built in Lab VIEW; along with a digital design developed within it. Fig 1. The signal enters directly via DAQ card.
A. Expected results for students profile support
The personal that works on the laboratory looks the next
topics for this scheme: to contribute in the formation of highly
qualified young Engineers in the Electronics,
Telecommunications and virtual instrumentation fields; to improve interpersonal relations between students participating in the educative model; generate a conscience in the users about the importance of team work; to improve the experimental knowledge of students. Figure 1. Spectrum analyzer for FFT in the NMFLV
B. Basic Configuration of the experiment
The experiment is based on a single circuit based on IC LM741, the setup of the operational amplifier in inverted signal. The input is a swept signal, the initial frequency is 500 KHz the final frequency is 1 MHz. The amplitude is 500 mV, the elapsed times is 5 seconds.
The operation of the VI is quite simple; the input signal provided by the function generator is entered to the operational amplifier is checked by NI-SCOPE, both input signal and output signal.
LabVIEW provides the tools to analyze this system. Spectral Measurement toolbox acquires input signal and output
signal, and then the signals are processed. The system behavior is monitored within LabVIEW using three waveform graphs. The suggested sequence is the following steps: • Sampling –from Fgen Soft- Labview
• Check initial sequence, adding new data and checking data acquisition process.
•
Split information (obtain mean value) to get peak frequency and peak potency.
• Spectrum screener from units selected and control change verification • The cycle ends, clears the data register if stop
泰安房产网信息网button is pressed.
• Check errors before exit the system. C. Spectrum analyzer description Each sample word consists of 64 bytes, which is stored in
the computer memory, the FFT is from Lab View, and this function uses Radix 2 decimation in time. The method consists of continuous sampling; the components are split into even and odd components, then is calculated the discrete Fourier transform.
Then the FFT is displayed on screen using built in function ‘Waveform Graph’, this calibrates automatic X and Y axis. The X axis is calibrated in frequency and Y axis is calibrated on amplitude, fig. 2.
D. Inverted amplifier with op-amp
The operational amplifier could be used in several applications, for being used in electronic devices and controls. An inverter amplifier is a circuit with constant gain if the feedback loop contents a fixed
resistor. The output is obtained by multiplying the input by a fixed gain or constant, due to input resistor and the feedback loop resistor, the output is inverted from the negative input. The gain is depicted in the following equation:
V 0= -(R f /R i )V i (1)
The circuit used on the experiment has R f = 100 [k Ω] –variable -, R i = 1 [k Ω], the gain of the output signal could be increased for 1 up to 100 times.
Figure 2. Screen of the sampling experiment, maximum frequency 20kHz
IV. A CTIVITIES ON THE EXPERIMENT
The guidelines for the experiments are: select the
福建旅游
攻略必玩的景点
appropriated VI for the experiment, from the shared directory, test the VI with a single circuit, and connect the wires to the specific circuit for the practice. After the initial setup for the experiments, the students playon the system with electronic circuits from different subjects, the laboratory is available for undergraduate students and post graduate students.
The surveillance of the experiment is provided via NETOP School, the person that is in charge of the experiment assigns the time based on previous scheduling for optimizing the number of participants per day.
For this experiment the student could realize easily, based on the screens on the fig. 4
Figure 3. Circuit schematic for the experiment.
For this paper the circuit was tested several times, the values are depicted in the following table.
TABLE I.
M AGNITUDE VALUES FROM THE TESTING CIRCUIT
Values from Input (FFT)
Output circuit
FFT
-29.164302 -37.483357 -32.220271 -39.515305 -69.210790 -54.116650
-63.348380 -62.324337 -61.330004 -64.436413 -67.431617 -62.161829 -66.434710 -61.889921 -59.289434 -53.275311 -60.244857 -55.424073
-73.775669 -61.901808 -65.517683 -63.753388 -65.805673 -68.573872
As it is depicted the values are so close due to the systems it is linear to frequency values up to 1000 KHz, when the systems signal is triggered above from this value the system
acts like a low pass filter.
Figure 4. Output screens for the VI
In the fig. 4 we could observe the white lines that represent inputs from the function synthesizer, like the equation (1) states the signal is inverted, the red lines only demonstrate that the amplifier follow afore mentioned equation.2008年汶川地震
A. Benefits of this work
The main benefits of the use of virtual instrumentation are the work that students undertake along they comprehend the physical behavior of the electronics, their knowledge willingness starts, due to the easy demonstrations of the classroom blackboard. Like other public universities in Mexico and abroad, the staff must solve the lack of resources within our deputies.
V.
C ONCLUSIONS AN
D FURTHER WORK
The attendants could understand in real time the Fast Fourier transform and the frequency response as well as the physical phenomenon. The students were clearly one step ahead of the classic framework of theory and laboratory. Within this classic structure the depiction of the theory it is not easy to understand, and while you have a professor and laboratory both in place and time.
In the forthcoming months the program will cover other subjects that are part of the academic program, that are more likely to be understand easy using VI instrumentation.
R EFERENCES
[1]Moumtadi, F, Reza Isabel, Vivente-Vivas E., Delgado J. Preliminary
Specifications and Operations of a Networking Model for a Virtual Radio Frequency Laboratory. In: 2009 International Conference on Engineering Education (ICEED 2009), December 7-8, 2009, Kuala Lumpur, Malaysia, unpublished
[2]Ko, C. H., Chen, B, M., Ramakrishnan, V.,Cheng, C.D. Zhuang, Y., and
chen J., “A Web-Based Virtual Laboratory on a Frequency Modulation Experiment”, IEEE Trans. Syst. Man, and Cyber.- Part C: applications and Reviews, Vol. 31, no. 3, August 2001, pp. 259-303. [3]Hasanul. A.B., Saliman A. Isa., and M´Hamed A. Henini., “Virtual
Laboratory for Electrical Circuit Course”. IEEE 2004.
[4]Plummer, M.C., Bittle C., and Karani, V., “A Circuit II Laboratory
Accessible by Internet,” Proc. 2002 American Society for Engineering Education.
[5]Kumar, BR., Sridharan, K., and Srinivasan, K., “The Design and
Development of a Webb-based Data AcquisitionSystem,” IEEE Trans.
Instr. And Measur., Vol. 51, No. 3, June 2002.
[6]Agrawal G. P. Fiber – Optic Communication Systems, 3ed, Wiley –
Interscience, EUA, 2002.
[7]Saleh B. E. A., Teich M.C. Fundamentals of Photonics, Wiley-
Interscience, EUA, 1991
[8]Chiang S. L. Physics of Optoelectronic Devices, Wiley-Interscience,
EUA, 1995
[9]Agrawal G. P., Dutta N. K., Semiconductor Lasers, 2ed, Van Nostrand
Reindhold, EUA, 1993
[10]Mynbaev D. K., Scheiner L., Fiber-Optic Communications Technology,
Prentice Hall, USA, 2001
