Ham Amateur Radio Technician Practice Exam

What is a distinctive feature of a direct digital synthesizer (DDS)?

1. Fixed output frequency

2. Variable output frequency with the stability of a crystal oscillator

3. Low power consumption

4. Easy to program

The correct answer is: Variable output frequency with the stability of a crystal oscillator

A direct digital synthesizer (DDS) is characterized by its ability to produce variable output frequencies while maintaining the stability associated with crystal oscillators. This functionality is vital because it allows for precise frequency generation that can be programmed or adjusted as needed. The digital nature of DDS enables it to achieve rapid frequency changes and fine resolution, which are essential for many modern communication applications. Unlike traditional frequency synthesis methods that might rely on analog components, DDS uses digital techniques to manage and generate frequencies. This digital approach ties back to the inherent stability of crystal oscillators, ensuring that the output it provides is stable and reliable. The ability to adjust the frequency on-the-fly, combined with its accuracy, is what sets DDS apart from older methods that might have fixed output frequencies or less reliability. While low power consumption and ease of programming are benefits associated with many modern technologies, they are not the most distinctive or defining aspects of a DDS compared to its frequency variability and stability. Hence, the combination of variable output frequency and the crystal oscillator's stability is what makes option B the correct choice.