The Spectrum Analyzer

Student: Andrew Buettner

Partner: - N / A -

Course Number: EL - 261

Experiment Number: #4

Professor: Vergers

Date Of Submission: Thu 06/Mar 03

Table Of Contents

Section Page Number

1) Cover Sheet.................................. 1

2) Table Of Contents.........................2

3) Objective.......................................3

4) Equipment Used............................3

5) Procedure......................................3

6) Results...........................................4

1) Diagram 1....................................4

2) Table 1.........................................5

3) Diagram 2....................................5

4) Diagram 3....................................5

5) Table 2.........................................6

6) Table 3.........................................6

7) Answers to Lab Questions.............6

8) Conclusions...................................7

9) Attachments...................................7

Objective

The objective of this lab is to become familiar with the high frequency spectrum analyzer by viewing the frequency spectra of frequency modulated and amplitude modulated waveforms.

Equipment Used

1) HP 3585 Spectrum Analyzer #3585A

2) HP 3311 Function Generator #1645

3) HP 3312A Function Generator #10468

Procedure

1) Assemble the equipment as shown:

2) Power the two signal generators and the spectrum analyzer and set their settings to the following:

a) HP 3311:

i) Dial to 4

ii) Frequency to 10KHz

iii) Sinewave

iv) Amplitude to 7 o'clock

b) HP 3312A

i) Dial to 4

ii) Frequency to 1MHz

iii) Modulation knob to 7 o'clock position

iv) Amplitude .01V

c) Spectrum Analyzer

i) 50W input impedance

ii) Continuous sweep

iii) Trace A

3) Press the step size button.

4) Press the up button until the step is 1,000,000Hz.

5) Press the Center Frequency button.

6) Press the down button fifteen times.

7) Press the Span button.

8) Press the down button until the span is 200KHz

9) Adjust the frequency dial until the HP3312A until a spike appears in the center of the screen.

10) Press the Marker button

11) Move the frequency dial until the marker is at the peak and record the frequency and dBm value.

12) Set the HP 3312A to external AM modulation with an amplitude of 1 Vpp.

13) Press Single Sweep on the analyzer and record the result.

14) Use the marker to record the dBm values and frequencies of the peaks.

15) Press Reference Level.

16) Record the voltages and frequencies using the marker.

17) Switch to continuous sweep.

18) Set the HP3312A to external FM with an amplitude of .01Vpp.

19) Set the analyzer to a span of 500KHz and record result.

20) Record the frequency of the peak and their respective voltage and dBm values.

Results

1) Diagram 1: Setup, Enlarged View

2) Table 1: Frequency and dBm Values for Single Wave

	Frequency:	dBm Value:
Sine Wave:	4,997,000Hz	-57.1dBm

3) Diagram 2: AM Frequency Spectrum

4) Diagram 3: FM Frequency Spectrum

5) Table 2: Frequencies, dBm Values, and Voltages for AM Wave

	Frequency:	dBm:	Voltage:
Center:	4,981,400Hz	-22.7dBm	1.64mV
LSB:	4,945,400Hz	-55.9dBm	636mV
USB:	5,017,600Hz	-55.3dBm	684mV

6) Table 3: Frequencies, dBm Values, and Voltages for FM Wave

	Frequency	dBm:	Voltage:
Center:	5,014,500Hz	-60.9dBm	202mV
FL1:	4,978,000Hz	-63.8dBm	144mV
FH1:	5,051,000Hz	-63.8dBm	144mV
FL2:	4,941,000Hz	-73.9dBm	45.2mV
FH2:	5,088,500Hz	-74.0dBm	44.6mV
FL3:	4,904,500Hz	-87.9dBm	9.04mV
FH3:	5,125,500Hz	-88.1dBm	8.80mV
FL4:	4,867,500Hz	-103.0dBm	1.58mV
FH4:	5,161,500Hz	-103.7dBm	1.46mV

Answers To Lab Questions

1) Q: What was the percent modulation of the AM wave?

A: m = .805

2) Q: What was the original unmodulated carrier amplitude of the FM signal?

A: E_c = 252mV

3) Q: What are the Bessel Functions of the FM wave?

A: J₀ = .80, J₁ = .57, J₂ = .18, J₃ = .04, J₄ = .01

4) Q: What is the modulation index of the FM wave?

A: m Z 1.25

5) Q: What was the frequency difference of the FM sidebands?

A: F_mavg = 36,750Hz

Conclusions

From this lab it, the basics of the spectrum analyzer is described. Also, the frequency spectra of both Frequency Modulation and Amplitude Modulation waves is described. For calculating the modulation index, the J values for the first half of the sidebands are high. I do not know what contributed to this error, but otherwise I feel that the lab is fairly accurate. A decent understanding of the spectrum analyzer has been obtained.

Attachments

Original lab handout
Original lab data
Calculations