CNET304 Lab 3 Amplitude Modulation (Haolong Li) PDF

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CNET304 Lab 3 Amplitude Modulation (Haolong Li)...

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Lab 4-AM Modulation

School of Engineering Technology and Applied Science (SETAS) Information and Communication Engineering Technology (ICET)

CNET 304 - Wireless Technology

Lab 3: Amplitude Modulation Prepared by: Dr. Sattar Hussain,  Centennial College, 2020

Section No. Group No. Name Obtained Mark Haolong Li (out of 25)

Student ID 301084324

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Due Date

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Learning Outcomes:

Lab 4-AM Modulation Upon completion of this lab, students will reliably demonstrate the ability to: - Set NI-Multisim Agilent Waveform Function Generator to produce AM or FM modulation - Verify mathematical expressions of AM & FM signal’s waveform and spectrum - Determine modulation index, power, and bandwidth from measurements for each AM & FM signal - Investigate and differentiate AM/FM/ASK/FSK signals Investigate and differentiate AM/FM/ASK/FSK signals in communication systems Pre-Lab Assignment [2 marks] 1. Does the carrier of an AM signal contain any information? Explain. The carrier of an AM signal is just a constant amplitude, constant frequency signal, so the only “information” it really contains is that the transmitter is switched on and connected to the transmitting antenna.

2. What percentage of the total power in an AM signal with m=100% is in the carrier? One sideband? Both sidebands? When the carrier is fully modulated 100% the amplitude of the modulation is equal to half that of the main carrier, the sum of the powers of the sidebands is equal to half that of the carrier, so both sidebands

Procedure

Lab 4-AM Modulation Task 1: Generating AM Signal 1. From the Start window of your computer or a shortcut on the desktop, run NIMultisim. 2. Construct the following schematic XSC1

XSA1

XFG1 Agilent

Tektronix P G

1 2 3 4

T

IN T

3. Turn on the Agilent Function Generator (XFG1). Generate AM signal with a sinewave carrier signal of f C=9x.0 kHz, amplitude V C=0.5 Vpp, modulated by sinewave modulating signal with f m=5 kHz at 75% modulation index (depth). Where x is the last digit of your student ID. For example, if your student ID is 3xxxxxx4, set the carrier frequency to 94.00 kHz. 4. Display the AM signal in the time domain (oscilloscope) and frequency domain (spectrum analyzer). 5. Turn on the Oscilloscope and adjust Ch. 1 vertical sensitivity to see the AM signal over 4-6 vertical divisions (check p-p max ~0.5 Vpp or less). Adjust the timebase to see 2-3 cycles of the AM waveform displayed in the Oscilloscope screen. 6. On the Spectrum Analyzer, set the Start frequency to 75 kHz, End frequency to 125 kHz, and the Amplitude to dBm. Set the Range to 20 dB/Div, Ref. -10 dB/Div, and 500 Hz Resolution. 7. [3 marks] Draw both AM waveform and spectrum below - accurately so your later calculations can be related to it. Record the setup values. On the waveform, label A (max p-p voltage of the AM signal) and B (min p-p). On the spectrum, label carrier (C), lower sideband (LSB), and upper sideband (USB).

Lab 4-AM Modulation

Waveform

Spectrum

Os c i l l o s c o p eSe t u p :

Sp e c t r u mAn a l y z e r Se t u p :

V/ d i v=……. .

REF=…………. CT RF R=……. . . . … SP AN=……. . ….

s / d i v =………

d B/ d i v=…. . …. . . .

Lab 4-AM Modulation

Lab 4-AM Modulation

Lab 4-AM Modulation

8. [1 marks] Record the following AM measurements in the table below:

AM Parameter

Measured Value

Max. Vp-p of AM Signal (mV)

100 mV

Min. Vp-p of AM Signal (mV)

0 mV

Carrier Power, P C (dB)

-18.865 dB

LSB or USB Power, PSB (dB)

LSB= -27.383 dB

Task 2: AM Signal Calculations 9. [2 marks] Calculate AM signal modulation index (m%) using the formulas provided in the Appendix on the last page. Write the formula, then write the measured values into the formula and calculate m%. Express all values in proper units and compare the two obtained results. Time Domain:

= (100-0)/(100+0)

Lab 4-AM Modulation =1 = 100% Frequency Domain:

= 0.75 = 75% So the AM signal modulation index in time domain is greater than the AM signal modulation index in frequency domain

10. [1 marks] Calculate the total power of the AM signal, P AM . Express the total power in mW and convert it to dB.

= 0.129867356*1mW+2*0.0018*1mW = 0.133467356 mW = -8.7462494286 dB

Lab 4-AM Modulation 11. [1 marks] Calculate the AM signal bandwidth (BW). Express all values in proper units

= 2|94kHz-89kHz| = 10 kHz

Task 3: Investigating Different AM Options 12. On the Function Generator, vary modulation index continuously by the knob 0% to 100% and observe the change in both the AM waveform and spectrum 13. [3 marks] Sketch the AM Waveform (Oscilloscope) and the spectrum (Spectrum Analyzer) for m=0%: Waveform

Spectrum

Os c i l l o s c o p eSe t u p :

Sp e c t r u mAn a l y z e r Se t u p :

V/ d i v=……. .

REF=…………. CT RF R=……. . . . … SP AN=……. . ….

s / d i v =………

d B/ d i v=…. . …. . . .

Lab 4-AM Modulation

14. [3 marks] Repeat step 13 for m=100% Waveform

Spectrum

Os c i l l o s c o p eSe t u p :

Sp e c t r u mAn a l y z e r Se t u p :

V/ d i v=……. .

REF=…………. CT RF R=……. . . . … SP AN=……. . ….

s / d i v =………

d B/ d i v=…. . …. . . .

[1 marks] Comment on the results obtained for m=0% and m=100%

Lab 4-AM Modulation

15. [5 marks] On the Function Generator, vary the modulating waveform (sine/triangle/square) and observe the AM signal (sketch AM waveform for the square and the Triangle waveforms below). To change the shape of the modulating signal, press Shift then Enter on the Function Generator. Use the ↑↓ keys to select AM SHAPE >> SINE. Use the → and ← to traverse over the different shapes, select the required shape>>Enter.

AM SIGNAL (Square Waveform) Waveform

Spectrum

Os c i l l o s c o p eSe t u p : Sp e c t r u mAn a l y z e r Se t u p : V/ d i v=……. . REF=…………. CT RF R=……. . . . … SP AN=……. . …. s / d i v =……… d B/ d i v=…. . …. . . .

Lab 4-AM Modulation

AM SIGNAL (Triangle Waveform) Waveform

Spectrum

Os c i l l o s c o p eSe t u p : Sp e c t r u mAn a l y z e r Se t u p : V/ d i v=……. . REF=…………. CT RF R=……. . . . … SP AN=……. . …. s / d i v =……… d B/ d i v=…. . …. . . .

Lab 4-AM Modulation

Appendix AM modulation index, power, and bandwidth can be calculated either from the waveform displayed on the oscilloscope or the AM spectrum displayed on the spectrum analyzer. TIME DOMAIN

FREQUENCY DOMAIN

vAM = (Ec + Em sin 2πfmt) sin 2πfct (carrier sinewave whose peak amplitude

Carrier peak Ec at frequency fc plus a pair of side-component peaks Esc = Em/2 at

Lab 4-AM Modulation changes proportionally to the modulating signal)

frequencies fc fm

Finding modulation index, power and bandwidth derived from the oscilloscope display:

Finding modulation index, power and bandwidth derived from the spectrum analyzer display:

A- B m= A + B , where A=Vmax & B= Vmin

, where ∆P(dB) = PSB(dBm)-PC(dBm),

PAM =Pc(1+

m2 E2 Pc = c ) 2R , 2 , where

where sc is side component (=side band, either one) Pc ( dBm) 10

Psc ( dBm) 10

(also Ec = (A+B)/4 )

PAM =10

(note: divide-by-2 includes peak-to-RMS conversion)

BW =2 fm, where fm = |fc- fSB|

BW =2 fm, where fm is intelligence frequency

|

*1mW + 2 *10

*1mW...