# seatwork prelim2018

```TECHNOLOGICAL INSTITUTE OF THE PHILIPPINES
College of Engineering and Architecture
Electronics and Engineering Department
SEATWORK COMPILATION
in
ECE 004 (PRINCIPLES OF COMMUNICATION)
Submitted By:
_____________________________
(name)
______________________________
(course/section)
MARCH 2019
TECHNOLOGICAL INSTITUTE OF THE PHILIPPINES
College of Engineering and Architecture
Electronics and Engineering Department
Principles of Communication
Seatwork No. 1
NOISE COMPUTATION 1
Name: ____________________________________
Course/Section: ____________________________
Score:
Date Submitted: __________
1. An amplifier operating over the frequency range of 455kHz to 460kHz has 200kΩ input resistor. What is the
RMS noise voltage at the input to the amplifier if the ambient temperature is 17degC. Ans: 4 microV
2. A mixer with input resistance of 300Ω has equivalent noise resistance of 100Ω. What is the noise voltage at the
input when the effective noise bandwidth is 25khz, the source voltage is 2µV and with internal resistance of
20Ω? Ans: 0.281microV
3. A three stage amplifier in cascade has the following parameters: Stage 1 has the gain of 5 and noise factor 2,
Stage 2 has a gain of 8 and noise factor 4, Stage 3 has a gain of 15 and a noise factor of 6. Find the overall noise
factor of the system. Ans: 2.725
TECHNOLOGICAL INSTITUTE OF THE PHILIPPINES
College of Engineering and Architecture
Electronics and Engineering Department
Principles of Communication
Seatwork No. 2
AMPLITUDE MODULATION 1
Name: ____________________________________
Course/Section: ____________________________
Score:
Date Submitted __________
1. 1. For an AM DSBFC wave with an unmodulated carrier voltage of 18Vp and a load resistance of 72
ohm, determine:
a. unmodulated carrier power
b. modulated carrier power
c. total sideband power
d. upper and lower sideband power
e. total transmitted power
2.. a. Write the expression of AM voltage wave of the following values: B. determine upper side frequency and
lower side frequency
Unmodulated carrier : 20Vp
Modulation coefficient = 0.5 mnodulating/carrier frequency = 5kHz/200kHz
3. Find the percent of modulation of an AM signal if 8V signal carrier is modulated by three different
frequencies with amplitudes 1V, 2, and 3V
TECHNOLOGICAL INSTITUTE OF THE PHILIPPINES
College of Engineering and Architecture
Electronics and Engineering Department
Principles of Communication
Seatwork No. 3
AMPLITUDE MODULATION 2
Name: ____________________________________
Course/Section: ____________________________
Score:
Date Submitted __________
1. For an AM envelope with a maximum peak voltage of 52V and minimum peak-to-peak voltage of 24V, what is
the percentage of modulation? Ans: m=0.625
2. During 100% modulation, what percentage of power saving for DSB transmission? Ans: 66.67%
3. An AM transmitter has a 1-kW carrier and is modulated by three different sine waves having equal
amplitudes. If effective modulation index is 0.8, calculate the individual values of modulation index.
Ans.m=0.462
4. An AM transmitter at 27 MHz develops 10W of carrier power into a 50-ohm load. It is modulated by
2-kHz sine wave between 20% and 90% modulation. Determine maximum and minimum waveform
voltage of the AM signal at 20%. Ans: Vmax=37.94V and Vmin=25.3V
5. An AM transmitter supplies 10kW carrier power to a 50-ohm load. It operates at a carrier frequency of
1.2MHz and is 80% modulated by a 3-kHz sine wave. Calculate the a)Vpeak voltage of the signal
b)USB frequency and peak amplitude c) LSB frequency and peak amplitude Ans; a.1148.90
b.400V , 1.203MHz c. 400V, 1.197MHz
```