DEE3144 Communication Fundamentals Due date: 10 May 2011 before 5.30pm

Assignment 2

1. What is the basic principle of FDM? 2. An ordinary broadcast television channel has a bandwidth of 6MHz. How many

radio stations (with a bandwidth of 200kHz each) could be accommodated in one television channel using FDM?

3. A selectivity curve of a tuned circuit is shown in the figure 3

with kHzfkHzfkHzfkHzf 40,10,30,20 4321 .

Figure: 3

i. Calculate the resonant frequency.

ii. Calculate the bandwidth if Q is equal to 2.5.

iii. Calculate the shape factor.

iv. Describe the relationship between Q and selectivity.

DEE3144 Communication Fundamentals Due date: 10 May 2011 before 5.30pm

4. A video signal with a baseband frequency range from 1MHz to 5MHz is

transmitted using linear PCM at 5 bits per sample. Calculate

i. Minimum Nyquist sample rate.

ii. The numbers of quantization levels.

iii. The maximum dynamic range in decibels.

iv. Name the process that reduces the dynamic range of the signal.

5. For a PCM system with a maximum audio input frequency of 4kHz.

i. Determine the minimum sample rate.

ii. The alias frequency produced if a 5kHz audio signal were allowed to enter the sampler.

6. Suppose a composite video signal with a baseband frequency range from dc to 4MHz is transmitted by linear PCM, using eight bits per sample and a sampling rate of 10MHz.

i. How many quantization levels are there?

ii. Calculate the bit rate.

7. An FM broadcast-band receiver tunes from 88 to 108MHz. The IF is 10.7MHz. Calculate the range of local oscillator frequencies.

8. A tuned circuit has a resonant frequency of 18MHz and a bandwidth of 120kHz. What are the upper and lower cutoff frequencies?

9. What circuit in a receiver compensates for a wide range of input signal levels?

10. Why crystal oscillators used instead of LC oscillators to set transmitter frequency?

DEE3144 Communication Fundamentals Due date: 10 May 2011 before 5.30pm

11. What is the noise voltage produced across a 50 input resistance at a

temperature of Co25 with a bandwidth of 2.5MHz? 12. Suppose the noise power at the input to a receiver is 1nW in the bandwidth of

interest. What would be the required signal power for a signal-to-noise ratio of 25dB?

13. The signal-to-noise ratio is 30dB at the input to an amplifier and 27.3dB at the

output.

i. What is the noise figure of the amplifier?

ii. What is the noise temperature?

14. The four stages of an amplifier have gains and noise figures (in decibels) as

follow: Calculate the overall gain and noise figure in decibels.

Stage Power Gain Noise Figure 1 12dB 2dB 2 15dB 4dB 3 20dB 6dB 4 17dB 7dB

15. Given that there is a 30 resistance at the input of receiver with a temperature of

Co20 and a bandwidth of 2MHz.

i. Calculate the noise voltage.

ii. Calculate the signal voltage if the SNR is 30dB.

iii. Calculate the noise figure if the S/N output is at 26.5dB.

iv. Calculate the noise temperature.