# E7H11 - What are the major spectral impurity components of direct digital synthesizers? **URL:** \ **Category:** Extra Questions\ **Created:** [January 2, 2026, 7:54pm UTC](https://forum.openhamprep.com/t/e7h11-what-are-the-major-spectral-impurity-components-of-direct-digital-synthesizers/1433 "2026-01-02T19:54:19Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![system](https://forum.openhamprep.com/uploads/default/original/1X/a8bc13ef992b522befd6b1d923d2f2a53605a9c7.png) [@system](https://forum.openhamprep.com/u/system)\ **Post date:** [January 2, 2026, 7:54pm UTC](https://forum.openhamprep.com/t/e7h11-what-are-the-major-spectral-impurity-components-of-direct-digital-synthesizers/1433/1 "2026-01-02T19:54:19Z")
## Question What are the major spectral impurity components of direct digital synthesizers? ## Answer Options - **A)** Broadband noise - **B)** Digital conversion noise - **C)** Spurious signals at discrete frequencies - **D)** Harmonics of the local oscillator **Correct Answer: C** * * * ## Explanation Direct Digital Synthesizers (\text{DDS}) are celebrated for their speed and fine-tuning resolution, but they suffer from a specific type of signal degradation unique to their digital architecture. This degradation is a form of phase noise or jitter caused by the quantization of the signal. The major spectral impurity components of \text{DDS} are **spurious signals at discrete frequencies** , often referred to as ‘spurs.’ These unwanted signals are generated by phase and amplitude errors caused by the finite number of bits used by the phase accumulator and the \text{DAC} in the synthesis process. While highly predictable, these spurs can require careful analog filtering to suppress before transmission. * * * _This topic was automatically created to facilitate community discussion about this exam question. Feel free to share study tips, memory tricks, or additional explanations!_