LABORATORY REPORT
Subject of the exercise:
Frequency domain analysis (Exercise 4.)
Date:
<year>. <month>. <day>
Location:
BME, Q.BP107
Students name:
<name 1>
<name 2>
Group and Desk No.
Group <No.>, Desk <No.>
Supervisor:
<name>
Measurement instruments
Digital multimeter
Agilent 34401A
<Serial No.>
Power supply
Agilent E3630
<Serial No.>
Function generator
Agilent 33220A
<Serial No.>
Oscilloscope
Agilent 54622A
<Serial No.>
Test board
VIK-05-01
Laboratory Exercises
1. Spectrums
Generate sine, triangular, square periodic waves by using the function generator. Display
spectrums of these signals on the oscilloscope (use the built-in FFT function).
1.1. Measure at least 10 harmonics of the periodic signals and compare to
theoretical values. What are the differences? What is the reason?
Let the amplitude be 2 Vpp in every case. The output load of the function generator
should be high impedance, otherwise the displayed values on the generator and the
oscilloscope are different. It is worth knowing that the oscilloscope displays the
result of the FFT in dBV which means that the reference is a sine signal with
amplitude 1 V rms.
<measurement setup>
1
f/f0
U
measured
2
3
4
5
6
7
8
9
10
11
[dBV]
U
[dBV]
theoretical
<comments, observations>
1
Report
1.2. Change the duty cycle of
spectrum?
the square wave. What does it cause in the
Note: low value for duty cycle can be set up in the Pulse menu.
<comments, observations>
1.3. Study the spectrum of a noise signal. Examine the differences with other
waves.
<comments, observations>
2. Analysis of Low-pass and High-Pass Filtering
Determine effects of low-pass and high-pass filtering in time and frequency domain,
respectively. During the measurement use square wave, and use the oscilloscope.
2.1. Use the first order, low-pass filter of the test board. Applying square wave
excitation examine the output signal in time and frequency domain,
respectively. What is the experience? Explain the results.
It is worth setting up the frequency of the square wave after calculating the cutoff
frequency (see the figure 4-6.).
<comments, observations>
2.2. Repeat the previous exercise using a high-pass filter on the same board. Let
the frequency be approximately 10 times smaller than the cutoff frequency of
the filter. What is the effect of the filter on the square wave?
<comments, observations>
2.3. Study the behavior of the oscilloscope in the case of a very low frequency
square wave. Check the effect of switching between AC and DC coupling. What
is the reason of the difference?
<comments, observations>
2.4. Measure a very high frequency square wave in the time domain. What is the
difference compared with the ideal square wave? Why?
<comments, observations>
3. Measuring amplitude characteristic by applying sine excitation
Measure the amplitude characteristic of the first order, low-pass filter. Use the sine wave
generator and the AC voltmeter. Display input and output signals on the oscilloscope.
3.1. Let the measurement range be between 2 decades lower and 1 decade over
the theoretical cutoff frequency. Use approximately logarithmic frequency scale.
2
Exercise 4
Frekvency domain analysis
A possible approximately logarithmic frequency scale is 1x, 2x, 5x, 10x the
theoretical cutoff frequency. For lower frequencies after shifting the same scale
can be used.
<comments, observations>
0.1
f [f/fc]
0.2
0.5
1
2
5
10
f [kHz]
Uout
[dB]
Uout [dB] measured
1.2
1
0.8
0.6
0.4
0.2
0
Uout [dB]
0
0.2
0.4
0.6
0.8
1
1.2
f [kHz]
3.2. Determine the real cutoff frequency by measuring the 3 dB point.
<comments, observations>
4. Measuring amplitude characteristic by applying high bandwidth periodic
signals
Measure the amplitude characteristic of the first order, low-pass filter on the board in
one step. The parameters of the filter (values of the resistors) can be set up by the switch.
4.1. Estimate the cutoff frequency by examining the input and output spectrums.
The excitation signal should be sine or multi sine wave. Determine the time
constant from frequency domain measurements! What kind of errors have
effect on the accuracy?
<comments, observations>
4.2. Use noise signal as excitation. Measure the amplitude spectrum of the output.
<comments, observations>
5. Measurement of non-linear distortion.
Measure the distortion of a sine wave.
5.1. Study the waveforms in time and frequency domains. In which domain can the
distortion be detected easier?
<comments, observations>
5.2. Calculate the distortion using the measured harmonics.
3
Report
<comments, observations>
Additional Laboratory Exercises
6. Spectrums of arbitrary periodic signals
6.1. Following guides of the instructor design a periodic signal and download into
the arbitrary function generator.
6.1.1. Check the spectrum by using the Fourier analyzer.
<comments, observations>
7. Measurement of the amplitude characteristic
7.1. Measure the amplitude characteristic of an unknown filter circuit.
7.1.1. Use sine wave generator and AC volt meter. Determine the cutoff
frequency.
<comments, observations>
7.1.2. Repeat the measurement by applying a selected excitation signal and
FFT. What kind of excitation signal should be used?
<comments, observations>
8. Fourier analyzer
8.1. Study the properties of Fourier analyses.
8.1.1. What is the effect of sampling? Which parameters have influences on the
frequency resolutions?
<comments, observations>
8.1.2. In which cases does leakage occur? How can it be avoided? Why are
windows used?
<comments, observations>
4