# Software Defined Radio with HackRF, Lesson 6

# Complex Numbers

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## in this lesson

- negative numbers
- complex numbers
- the complex plane
- complex arithmetic
- complex exponentials
- tau
- rectangular coordinates and polar coordinates
- complex number terminology
- quadrature terminology

## homework

- A weather station measures wind direction once per minute. Write a program to indicate the average direction over a five minute period. Try it on the following sets of readings:
- 12°, 15°, 13°, 9°, 16°
- 358°, 1°, 359°, 355°, 2°
- 210°, 290°, 10°, 90°, 170°
- Modify your program to handle wind speed input in addition to direction.

## resources

- The Tau Manifesto
- My favorite introductory DSP book: Practical Signal Processing by Mark Owen
- Another interesting alternative to classical trigonometry is rational trigonometry. I particularly recommend it if you are interested in triangles and geometry rather than periodic phenomena.

Software Defined Radio with HackRF is copyright 2014, 2015 by Michael Ossmann and is released under the CC BY license.