148. Which of the following is the main advantage of PCM system?
A. Lower noise
B. Lower power
C. Lower band-width
D. None of the above

---

149. By the use of which of the following low speed TDM is produced?
A. Delay lines
B. Pulse oscillators
C. Electronic switching circuits
D. Rotating switches

---

150. The term noise temperature is used for which of the following?
A. Thermal-noise source only
B. White-noise source only
C. Non-thermal-noise source only
D. All of the above

---

151. Which of the following measures cannot be used to reduce noise?
A. By reducing the singnalling rate
B. By using redundancy
C. By increasing the channel bandwidth
D. By increasing the transmitted power

---

152. With reference to 'noise temperature' which of the following statements is correct?
A. It is a measure of noise figure of a receiver
B. It is the same as physical temperature of the body
C. It is a measure of the available noise power for non-thermal sources
D. None of the above

---

153. The power-density spectrum is a function
A. square
B. linear
C. odd
D. even

---

154. The power-density spectrum represents power per unit
A. wavelength
B. bandwidth
C. frequency
D. none of the above

---