Chapter 9 / 9.5

9.5 REVISION QUESTIONS

1. Draw the block diagram of a low-level AM transmitter and briefly outline the main functions of each section.

1. Draw the block diagram of a high-level AM transmitter.

1. Draw the block diagram of an FM transmitter.

1. Briefly describe the purpose of the pre-emphasis / de-emphasis networks in FM transmitters and receivers.

1. Briefly describe the three transmitter performance criteria: power, frequency stability, and spurious output.

1. Explain how direct-conversion (homodyne) architectures differ from classical heterodyne transmitters, and identify the principal impairments that must be corrected in modern implementations.

1. Describe the function of a digital up-converter (DUC) and explain how it contributes to spectral shaping and regulatory compliance in SDR transmitters.

1. Discuss the role of digital predistortion (DPD) in maintaining transmitter linearity and how it interacts with the power amplifier characteristics.

1. Modern SDR transmitters are said to be reconfigurable and frequency-agile. Explain what this means in practice, and describe how software control enhances adaptability compared with fixed analogue architectures.

1. Draw the block diagram of an AM superheterodyne receiver. Briefly describe the function of each of the blocks.

1. Draw the block diagram of an FM superheterodyne receiver. Briefly describe the function of each of the blocks.

1. The RF stage of a superheterodyne receiver consists of an RF amplification section and a pre-selection section. Explain the function of each of these sections. Explain the origin of the troublesome frequencies that the Pre-selection Section is designed to eliminate.

1. Briefly describe the function of the local oscillator (LO) in a superheterodyne receiver. What are the desirable characteristics of the receiver LO?

1. Describe the functions of the IF amplifier in a superheterodyne receiver.

1. Briefly describe the operation and purpose of automatic gain control (AGC) in a superheterodyne receiver.

1. Briefly describe the operation and purpose of squelch in a superheterodyne receiver.

1. Briefly explain the receiver performance criteria of: noise figure, sensitivity, selectivity, fidelity, dynamic range, and third-order intermodulation products.

1. Compare the operating principles of double- and triple-conversion receivers with those of single-conversion superheterodynes. Why are multiple IFs advantageous in some applications?

1. Outline the benefits and limitations of the zero-IF (homodyne) receiver architecture, and explain how modern systems compensate for LO leakage and I/Q imbalance.

1. Define a software-defined radio (SDR) receiver and describe the roles of the ADC and DDC in its signal-processing chain.

1. What distinguishes a cognitive receiver from a conventional SDR, and how do adaptive or machine-learning techniques improve spectrum utilization and interference mitigation?

1. Identify the main hardware and DSP features that allow modern receivers to achieve thermal-noise-limited sensitivity and high linear dynamic range within a multi-standard platform.