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## EENG 3810 Chapter 4

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**EENG 3810 Chapter 4**Amplitude Modulation (AM) 1**Chapter 4 Homework**1. For an AM DSBFC modulator with a carrier frequency fc = 200KHz and a maximum modulating signal frequency fm(max) = 10 KHz, determine : a. Frequency limits for the upper and lower sidebands. b. Bandwidth. b. Upper and lower side frequencies produced when the modulating signal is a single-frequency 6 KHz tone. 2**Homework Continued**2. For the AM wave form above determine: 3**Homework Continued**3. 4**Homework Continued**• Repeat steps (a) through (d) in Example 4 in these lecture slides for a modulation coefficient of 0.5. • For an AM DSBFC wave with a peak unmodulated carrier voltage Vc = 20 Vp, a load resistance RL = 20 , and a modulation coefficient m = 0.8, determine the power of the modulated wave 5**Homework Continued**6.Determine the noise improvement for a receiver with an RF bandwidth equal to 100 KHz and an IF bandwidth equal to 20 KHz.**Frequency Spectrum of An AM Double Sideband Full Carrier**(DSBFC) Wave 9**Example 1**For an AM DSBFC modulator with a carrier frequency fc = 100KHz and a maximum modulating signal frequency fm(max) = 5 KHz, determine : a. Frequency limits for the upper and lower sidebands. b. Bandwidth. c. Upper and lower side frequencies produced when the modulating signal is a single-frequency 3 KHz tone. 10**Example 1 Solution**a. b. c. 11**Phasor addition in an AM DSBFC envelope**• For a single-frequency modulating signal, am AM envelop is produced from the vector addition of the carrier and upper and lower side frequencies. Phasors of the carrier, • The upper and lower frequencies combine and produce a resultant component that combines with the carrier component. • Phasors for the carrier, upper and lower frequencies all rotate in the counterclockwise direction. • The upper sideband frequency rotates faster than the carrier. (usf> c) • The lower sideband frequency rotes slower than the carrier. (usf< c) 13**If the modulating signal is pure, single frequency sine wave**and the modulation process is symmetrical, the % modulation can be derived as follows: 16**Peak Amplitudes of Upper and Lower Sidebands**The peak change in amplitude of the output wave (Em) is equal to the sum of the voltages from the upper and lower sideband frequencies. Therefore, 17**Percent Modulation of An AM DSBFC Envelope(a) modulating**signal; (b) unmodulated carrier; (c) 50% modulated wave; (d) 100% modulated wave 18**Example 2**For the AM wave form above determine: 19**Example 2**20**Generation of an AM DSBFC Envelope Shown in The Time Domain**–½ cos(230t) sin(225t) + ½ cos(220t) summation of (a), (b), and (c) 22**Example 3**24**Power Spectrum for an AM DSBFC Wave with a Single-frequency**Modulating Signal 30**Example 4**31**Single-side Band Full Carrier (SSBFC)**The carrier is transmitted at full power and only one sideband is transmitted.**Single-Sideband Suppressed Carrier (SSBSC)**The carrier is suppressed 100% and one sideband is removed. Only one sideband is transmitted.**Single-Sideband Reduced Carrier(SSBRC)**One sideband is removed and the carrier voltage is reduced to 10% of its un-modulated amplitude.**Independent Sideband(ISB)**A single carrier is independently modulated by two different modulating signals.**Vestigial Sideband(VSB)**The carrier and one complete sideband are transmitted, but only part of the other sideband is transmitted.