I. Identify the band of each of the following frequencies.
(a) 10 MHz (used for standard time and frequency broadcasts)
(b) 2.45 GHz (used for microwave ovens)
(c) 100 kHz (used for the LORAN navigation system for ships and aircraft)
(d) 4 GHz (used for satellite televisioó)
(e) 880 MHz (used for cellular telephones)
2. Suppose that a voice frequency of 400 Hz is transmitted on an AM radio station operating at 1020 kHz. Which of
these frequencies is
(a) the information frequency?
(b) carrier frequency?
(c) the baseband frequency?
(d) the modulating frequency?
3. Which parameters of a sine-wave carrier can be modulated?
4. Explain briefly the concept of frequency-division multiplexing and give one practical example of its use.
5. Explain briefly the concept of time-division multiplexing and give one practical example of its use.
6. Describe what is meant by each of the following types of distortion:
(a) harmonic distortion
(b) nonlinear frequency response
(c) nonlinear phase response
What is the theoretical bandwidth of a I kHz square wave?
(b) Suggest a bandwidth that would give reasonably good results in a practical transmission system.
(c) Suppose that a I kHz square wave is transmitted through a channel that cannot pass frequencies above 2 kHz.
What would the shape of the wave be after passing through the channel?
8. Describe the way in which each of the following types of noise is generated:
(a) equiþment (e) shot
(b) atmospheric (f) partition
(c) space (g) excess
(d) thermal (h) transit-time
9. What is the difference between white and pink noise?
10. What is meant by the noise power bandwidth of a system?
l l . Why is the noiseTower bandwidth greater than the halfpower bandwidth for a typical bandpass filter?
12. Why are amplifiers that must work with very weak signals sometimes cooled to extremely low temperatures?
What is this process called?
13. What is meant by the signal-to-noise ratio? Why is it impor tant in communication systems?
14. Give two ratios that are similar to the signal-to-noise ratio and are easier to measure.
15. Explain how noise figure is related to signal-to-noise ratio.
16. What is the relationship between noise figure and noise temperature?
17. Explain why- the first stage in an amplifier is the most important in determining the noise figure for the entire
amplifier.
18. Name the two basic types of spectrum analyzer, and briefly describe how each works.
19. Name the four most important controls on a sweptfrequency spectrum analyzçr, and describe the function of
each.
20.What happens to the noise level displayed on a spectrum analyzer as its bandwidth is increased? Why?
Section
21. Visible light consists of electromagnetic radiation with
Wavelengths between 400 and 700 nanometers (nm). Express
this range in terms of frequency.
22. Equation (1.3) applies to any kind Of wave. The velocity Of
sound waves in air is about 344 rn/s. Calculate the Wave-
length Of a sound wave with a frequency Of I kHz.
Section
1.3
23. Sketch the spectrum for the half-wave rectified signal in
Figure I .21, showing harmonics up to the fifth. Show the
voltage and frequency scales, and indicate whether your
voltage scale shows peak or RMS voltage.
17 v
8.335 16.67
t (ms)
Figure
24. Sketch the frequency spectrum for the triangle wave shown in
Figure 1.22, for harmonics up to the fifth. Show the volt-
t (IIS)
Figure
25. A I kHz square wave passes through each of three communication
channels whose bandwidths are given below. Sketch the output in
the time domain for each case.
I(žkHz
(b) 2kHzt04kHz
(c) 0 to 4 kHz
26. Sketch the spectrum for the pulse train shown in Figure .23.
o 10 20 30 40 50 60
t (ns)
Figure
27. Sketch the spectrum for the sawtooth waveform in Figure
1.24. Explain why this waveform has no dc component,
unlike the sawtooth waveform in Example 1.3.
3
> o
t
(ms
)
Figure 1.24
Sectlan 1.4
28. A 50 resistor operates at room temperature (21 oc). How much noise power does
it provide to a matched load over the bandwidth of
(a) a CB radio channel (10 kHz)?
(b) aTV channel (6 MHz)?
Express your answers in both watts and dBm.
29. What would be the noise voltage generated for each of the conditions in Problem
28?
30. Calculate the noise current for a diode with a bias current of 15 mA, observed
over a 25 kHz bandwidth.
31. The signal-to-noise ratio is 30 dB at the input to an
amplifier and 27.3 dB at the output.
(a) What is the noise figure of the amplifier?
(b) What is its noise temperature?
32. (a) The signal voltage at the input of an amplifier is 100
V.V, and the noise voltage is 2 ILV. What is the signal-to-
noise ratio in decibels?
(b) The signal-to-noise ratio at the output' of the same
amplifier is 30 dB. What is the noise figure of the
amplifier?
33. (a) A receiver has a noise temperature of 100 K. What is its
noise figure in decibels?
(b) A competing company has a receiver with a noise
tem perature of 90 K. Assuming its other
specifications are equal, is this receiver better or
worse than the one in part (a)? Explain your answer.
34. Suppose the noise power at the input to a receiver is I
nW in the bandwidth of interest. What would be the
required signal power for a signal-to-noise ratio of 25
dB?
