TEL 312 INTRODUCTION TO ELECTRONIC
COMMUNICATIONS FUNDAMENTALS
LAB EXPERIMENT 1
FREQUENCY DOMAIN CHARACTERISTICS OF SIGNALS
SPRING 2009
Date of lab:
Lab report due:
Tuesday, Jan. 20, 2009
Friday, Jan. 30, 2009 @ 5 pm
Lab report guidelines:
Copy all the screen shots from the spectrum analyzer into a MS Word document
(or other word processor). In the same file, write a 1 to 2 page summary of the
experiment. Submit the completed report electronically to [email protected]
Hand in the completed lab handout and Prelab by Friday, Jan. 30. Every one must
do their own report for Lab 1.
The 1 to 2 page summary should explain clearly and accurately:
What the electromagnetic spectrum is
What a spectrum analyzer is & what information it displays
What bandwidth means & how it is measured on the spectrum analyzer
Explain what you did in the experiment & refer to the screen shots to explain
the results
Explain why this lab was useful. If this lab could be improved, mention what
parts were not useful or confusing and provide suggestions for improvement.
Write the summary as if you were writing it for someone who does not have an
engineering background. For example, assume that the reader does not know what
bandwidth is. Consider your audience as the readership of a newspaper with at
least an eighth grade education.
FREQUENCY DOMAIN CHARACTERISTICS OF SIGNALS
Purpose:
The objectives of this laboratory are:
1. To introduce the Agilent spectrum analyzer.
2. To identify various types of signals.
3. To analyze frequency domain characteristics of the signals.
Equipment List
1.
2.
3.
4.
5.
6.
Agilent N1996A Spectrum Analyzer
Agilent 33250A Function Generator
VHF Telescoping Antenna
USB flash drive
Laptop computer
AM/FM Portable Radio
Prelab Questions.
1. A spectrum analyzer screen shot of a signal and its harmonics is shown below.
(a) What are five peak powers in dBm? Do not include the power at 0 Hz.
(b) What are the corresponding frequencies of the five peak powers?
2. In the spectrum analyzer screen shot shown below, determine:
(a) The peak power in dBm
(b) The frequency per division in kHz.
(c) The frequency at which the peak power occurs.
(d) The start frequency of the screen shot (on the extreme left).
(e) The stop frequency of the screen shot (on the extreme right).
3. In the spectrum analyzer screen shot shown below, determine:
(a) The peak power in dBm.
(b) The frequency per division in kHz.
(c) The 20 dB bandwidth in kHz .
(d) The lower and upper frequency limits of the 20 dB bandwidth in MHz.
(e) The noise floor in dBm.
4. In the figure below, sketch a signal having the following characteristics:
•
•
•
Peak power of -35 dBm at 1.60 GHz,
5 dB bandwidth of 200 MHz, and
30 dB bandwidth of 300 MHz.
Include in the sketch a noise floor of -80 dBm.
Lab Procedures
Note : Spectrum analyzer button sequences are displayed in BOLD font.
1. Power on the Agilent N1996A Spectrum Analyzer
2. Power on the Agilent 33250A Function Generator.
3. Set up the Agilent 33250A Function Generator to generate a SINE wave with the
specifications:
fm = 80 MHz.
Am = 100 mVrms,
4. Display this waveform on the oscilloscope so that it shows 2 cycles of the wave form.
Adjust the vertical up/down knob to center the ground reference on the x-axis. Use the
quick measure button to determine the frequency and peak-to-peak voltage of the
waveform. Records results here:
Peak-to-peak voltage = ____________
Frequency = _____________
⎛ V pp
Calculate the RMS voltage: RMS voltage = ⎜⎜
⎝ 2
⎞
⎟⎟(0.707 ) = __________
⎠
5. Connect the function generator output to the spectrum analyzer input. On the spectrum
analyzer, set the center frequency to 80 MHz and the span to 1 MHz.
FREQ Button ⇒ Center Freq soft key ⇒ 80 on keypad ⇒ MHz soft key
SPAN Button ⇒ SPAN soft key ⇒ 1 on keypad ⇒ MHz soft key
6. Record below the peak power level at 80 MHz. From the function generator voltage and
an assumed 50 Ω resistance of the spectrum analyzer, compute the expected power level
in dBm. Show calculations below.
Measured power level = __________ dBm
Calculated power level = __________ dBm
7. Describe what the frequency spectrum of a sine wave looks like.
8. The lab instructor has a collection of radio frequency (RF) connectors. Find the
appropriate connector to connect a VHF telescoping antenna to the RF INPUT of the
spectrum analyzer.
9. Power on a laptop.
10. Tune the AM/FM radio to the radio station WWCU-FM @ 90.5 MHz.
11. Set the center frequency of the spectrum analyzer to 90.5 MHz.
FREQ Button ⇒ Center Freq soft key ⇒ 90.5 on keypad ⇒ MHz soft key
12. Set the frequency span to 300 kHz.
SPAN Button ⇒ SPAN soft key ⇒ 300 on keypad ⇒ kHz soft key
13. If the noise floor is not clearly visible, then raise the amplitude of the display until you
see the entire noise floor.
AMPTD Button ⇒ turn the wheel counter–clockwise
14. Perform a Max hold of the displayed frequency spectrum
Trace/Detector Button ⇒ Max Hold soft key
15. Select a second trace (blue) to show instantaneous power.
Trace/Detector Button ⇒ Select Trace soft key to select trace 2
⇒ Clear Write soft key
16. You should now have two traces displayed in two different colors; one showing
instantaneous power and the other showing max hold power.
17. Place a marker on the Max Hold trace. Marker Button (without the arrow)
18. If the marker is on the instantaneous power trace, then move it to the Max Hold trace.
Marker Button ⇒ More 1 of 2 soft key ⇒ Marker Trace soft key
19. Measure the Peak power and record in Table 1.
Peak Search Button ⇒ peak power is displayed in top right corner
20. Measure the 10 dB lower and upper cutoff frequency and record in Table 1.
Turn wheel to the left to 10 dB below peak
⇒ lower cutoff freq is displayed in top right corner
⇒ Turn wheel to the right to 10 dB below peak
⇒ upper cutoff freq is displayed in top right corner
21. Measure the 10 dB bandwidth and record in Table 1.
Turn wheel to the lower cutoff freq ⇒ Marker Button ⇒ Delta soft key
⇒ Turn wheel to the upper cutoff freq so that ΔMKR 1 is with the range ±1 dB
⇒ Bandwidth is displayed in top right corner
22. Measure the 20 dB bandwidth and record in Table 1.
Marker Button ⇒ Normal soft key⇒ Turn wheel to the lower 20 dB cutoff freq
⇒ Delta soft key
⇒ Turn wheel to the upper cutoff freq so that ΔMKR 1 is with the range ±1 dB
⇒ bandwidth is displayed in top right corner
Have the instructor inspect the display. Instructor initials___________
23. Save a screen shot of the WWCU-FM frequency spectrum to a USB flash drive. The
instructions for saving a screen shot are provided in the handout entitled: Operations of
the Agilent N1996A Spectrum Analyzer.
24. Pull the screen shot up on a laptop to make that the screen shot is saved on the flash drive.
Screen Shot File Name_______________________
25. Another radio station is located at 99.5 MHz. Tune the radio to this station.
26. Set the start frequency of the spectrum analyzer to 99 MHz
FREQ Button ⇒ Start Freq soft key ⇒ 99 on keypad ⇒ MHz soft key
27. Set the start frequency of the spectrum analyzer to 100 MHz
FREQ Button ⇒ Start Freq soft key ⇒ 100 on keypad ⇒ MHz soft key
28. Set the amplitude scale per division to 5 dB/div.
AMPTD Button ⇒ Scale/Div soft key ⇒ 5 on keypad ⇒ dB soft key
29. Measure the Peak Power in dBm and the 10 dB and 20 dB bandwidths of the radio station
at 99.5 MHz. Record data in Table 1.
When you have completed the 20 dB bandwidth measurement at 99.5 MHz, have the
instructor inspect the display. Instructor initials___________
30. Save a screen shot of the spectrum analyzer to a USB flash drive.
31. Pull the screen shot up on a laptop to make that the screen shot is saved on the flash drive.
Screen Shot File Name_______________________
32. The instructor is sending some music to a FM transmitter in the classroom. We will call
this radio station Belk 355 – FM. Make sure the radio transmitter is turned on. This
classroom radio station is at 89.7 MHz, the same frequency of another radio station,
WCQS. Tune the radio to find radio station Belk 355 – FM.
33. Select appropriate start and stop frequencies to display the frequency spectrum of the
radio station within the classroom. Follow the steps above to measure the10 and 20 dB
bandwidths and peak power. Fill in the information in Table 1.
34. Save a screen shot of the spectrum analyzer to a USB flash drive.
35. Pull the screen shot up on a laptop to make that the screen shot is saved on the flash drive.
Screen Shot File Name_______________________
36. A pace is equal to two steps at a normal gait and is about 5 feet. Standing at the radio
station antenna of Belk 355 – FM, walk away and out of the classroom counting paces.
As you are walking away, the Belk 355 radio station will be overtaken by another radio
station.
How far did you walk until the Belk 355 signal broke up?
# of paces = __________________
Distance = # of paces × 5 = ____________________ feet
.
Table 1 – Spectrum Analyzer measurement of radio station frequency characteristics
Radio
Measured
Low freq High freq
Measured
Radio
station
Peak
Type of
cutoff in
cutoff in
Bandwidth in
center
station
bandwidth
Power in
frequency
MHz
MHz
kHz
name
dBm
in MHz
WWCUFM
90.5
unknown
99.5
Belk 355
- FM
89.7
10 dB
20 dB
10 dB
20 dB
10 dB
20 dB