Chapter 3 - Modulation Flashcards
1
Q
- Sketch an AMDSB signal in the time and frequency domains. Label the main components of the signal.
A
2
Q
- Contrast and compare AMDSB and DSBSC in the frequency domain.
A
-
AMDSB:
- The AMDSB signal includes both the carrier frequency and two sidebands (upper and lower) containing the same information.
- In the frequency domain, the carrier appears as a strong central peak, with sidebands symmetrically located on either side.
- The bandwidth required for AMDSB is twice the frequency of the highest modulating signal.
-
DSBSC:
- DSBSC transmits only the two sidebands without the carrier.
- In the frequency domain, the carrier peak is absent, resulting in only the sidebands being visible.
- The bandwidth required for DSBSC is the same as for AMDSB, but without the carrier, it is more power-efficient.
While both occupy the same bandwidth, DSBSC is more efficient as it eliminates the carrier, allowing more power to be dedicated to transmitting the information-carrying sidebands.
3
Q
- Compare the bandwidth of AMDSB and AMISB if both sidebands are the same bandwidth.
A
4
Q
- Why do we use a pilot carrier in AM?
A
- Provide a frequency reference: Ensures accurate demodulation.
- Enable synchronization: Keeps the receiver in sync with the transmitted signal.
- Improve demodulation accuracy: Reduces errors in signal reconstruction.
5
Q
- With the aid of a diagram (WTAD) demonstrate how a carrier signal is baseband modulated in an FM system. What effect occurs when an FM signal falls below a certain level?
A
6
Q
- What functions accurately measure the bandwidth of an FM signal?
A
Spectrum Analyser
Carsons Rule
Fast Fourier Transform
7
Q
- If an FM system has a modulating baseband with a period of 250 ms and the maximum and minimum frequency outputs are 100 MHz and 99.85 MHz respectively. What is the Carson Bandwidth?
A
Carsons BW = 2(∆f + fm)
∆f = (fmax - fmin) / 2
Fm = 1 / Tm
∆f = (100Mhz - 99.85Mhz) / 2 = 0.075 = 75kHz
fm = 1 / 0.25s = 4 Hz
BW = 2(75000 Hz + 4 Hz) = 158kHz
