Download UNIVERSITI MALAYSIA PERLIS

UNIVERSITI MALAYSIA PERLIS
Pusat Pengajian Kejuruteraan Komputer dan Perhubungan
Semester 2, 2015/2016
DKT 226 – Basic Communication Engineering
TUTORIAL 2
TUTORIAL
1:
NOISE
ANDModulation
TRANSMISSION
CHAPTER 2: Amplitude
(AM) MEDIA & EM
PROPAGATION
Part A: AM Transmission
1. Define the following terms:
a. Amplitude modulation
b. Modulating signal
c. Carrier signal
d. AM envelope
e. Modulation coefficient
2. What is the maximum modulating signal frequency that can be used with an AM
DSB-FC system with a 20-kHz bandwidth?
3. For a maximum positive envelope voltage of +12V and a minimum positive
envelope amplitude of +4V, determine the modulation coefficient and percent
modulation.
4. For an AM DSB-FC envelope with a +Vmax = 40V and +Vmin = 10V, determine:
a. Unmodulated carrier amplitude
b. Peak change in amplitude of the modulated wave
c. Coefficient of modulation and percent modulation
5. For an unmodulated carrier amplitude of 16Vp and modulation coefficient m =
0.4, determine the amplitudes of the modulated carrier and side frequencies.
6. For an AM modulator with a carrier frequency fc = 200 kHz and a maximum
modulating signal frequency fm(max) = 10kHz, determine:
a. Frequency limits for the upper and lower sidebands.
b. Upper and lower side frequencies produced when the modulating signal is
a single-frequency 7-kHz tone.
c. Bandwidth necessary to pass the maximum modulating signal frequency.
d. Draw the output spectrum
7. One input to an AM DSB-FC modulator is an 800-kHz carrier with an amplitude
of 40Vp. The second input is a 25-kHz modulating signal whose amplitude is
sufficient to produce a ±10V change in the amplitude of the envelope.
Determine:
a. Upper and lower side frequencies.
b. Modulation coefficient and percent modulation
c. Maximum and minimum positive peak amplitudes of the envelope.
d. Draw the output frequency spectrum
e. Draw the envelope.
8. For an unmodulated carrier amplitude of 12Vp and a modulation coefficient of
0.5, determine:
a. Percent modulation
b. Peak voltages of the carrier and side frequencies.
c. Maximum positive envelope voltage.
d. Minimum positive envelope voltage.
e. Sketch the envelope.
9. For an AM DSB-FC wave with an unmodulated carrier voltage of 25Vp and a
load resistance of 50Ω, determine:
a. Power in the unmodulated carrier
b. Power of the modulated carrier, upper and lower sidebands and total
transmitted power for a modulation coefficient m = 0.6.
10. Write an expression for an AM voltage wave with the following values:
Unmodulated carrier = 20Vp
Modulation coefficient = 0.4
Modulating signal frequency = 5 kHz
Carrier frequency = 200 kHz
11. For an AM DSBFC wave with 15 Vp unmodulated carrier voltage, a load resistor
of 150 Ω and modulation index of 0.75, determine:
a. Power of the carrier
b. Upper and lower sidebands power
c. Total power of the modulated wave
d. Draw the power spectrum
Part B: AM Reception
1. Define the following terms:
a. Selectivity
b. Shape factor
c. Bandwidth improvement
d. Sensitivity
e. Fidelity
2. Briefly explain the difference between a coherent and noncoherent radio receiver.
3. Draw the block diagram for a TRF radio receiver and briefly describe its
operation.
4. What are the disadvantages of a TRF receiver?
5. Draw the lock diagram for an AM superheretodyne receiver and describe its
operation.
6. For a receiver with IF, RF and local oscillator frequencies of 455 kHz, 900 kHz
and 1355 kHz, respectively, determine:
a. Image frequency.
b. IFRR for a preselector Q of 80.
7. For a citizens band receiver using high-side injection with an RF carrier of 27.04
MHz and a 10.645 MHz IF, determine:
a. Local oscillator frequency.
b. Image frequency.
Part C: AM SSB Communications
1. For an AM Double-sideband full-carrier (DSB-FC) with a peak unmodulated
carrier voltage, Vc = 20Vp and a frequency of 200 kHz, a load resistor of 50Ω,
frequency of modulating signal of 20 kHz and modulation index of 0.75,
determine:
a. Powers of the carrier and the upper and lower sidebands.
b. Total power of the modulated wave.
c. Bandwidth of the transmitted wave.
d. Draw the power and frequency spectrum
2. For the same AM DSB-FC as Question 1, determine Q1(b) – Q1(d) for the
following systems. Also, determine the percentage of power saved in each of the
system design.
a. AM DSB-SC
b. AM SSB-FC
c. AM SSB-SC