<< Chapter < Page Chapter >> Page >
This module is part of the collection, A First Course in Electrical and Computer Engineering . The LaTeX source files for this collection were created using an optical character recognition technology, and because of this process there may be more errors than usual. Please contact us if you discover any errors.

Notes to teachers and students:

Filtering is one of the most important things that electrical and computer engineers do. In this chapter we extend everyday understanding of filters to numerical filters. We then study weighted moving averages and exponential averages. We define the important test signals for electrical and computer engineering and show how filters respond to them. The idea that filters are characterized by their response to simple test signals is fundamental. In the numerical experiment , students explore the frequency response of a simple filter, a concept that forms the basis of circuit theory, electronics, optics and lasers, solid-state devices, communications, and control.

Introduction

A filter is any device that passes material, light, sound, current, velocity, or information according to some rule of selectivity. Material (or mechanical) filters are commonplace in your everyday life:

  1. coffee filters pass flavored water while filtering out coffee grounds;
  2. Goretex fibers pass small, warm perspiration droplets while filtering out large, cool droplets of rain or snow;
  3. fiberglass strands in a furnace filter pass warm air while filtering out particles of dirt and dust;
  4. a centrifuge retains material of low density while spinning out (or filtering out) material of high density; and
  5. an electrostatic precipitator filters out dust and other effluents by attaching charge to them and using an electric field to move the charged particles to a high potential drain.

The first three of these examples selectively pass material according to size; the last two selectively pass material according to its mass density.

Typical filters for light are

  1. UV filters on camera lenses and eyeglasses that pass light in the range of visible wavelengths while blocking light in the invisible (but damaging) ultraviolet range;
  2. polaroid lenses that pass light that is randomly polarized while blocking out glare that is linearly polarized;
  3. green fabrics that reflect green light and absorb other colors;
  4. red taillights that pass light in the long wavelength red range and reflect light in the short wavelength violet range (look at the inside of your taillights to see violet); and
  5. glacial ice that absorbs all but the blue wavelengths so that it appears blue.

Satellite Television. Among current filters, the tuner in a super-heterodyne receiver is, perhaps, the first example that comes to mind. But satellite TV filters are another fascinating example. A typical C-band satellite has twelve transponders (or repeaters), each of which transmits microwave radiation in a personalized 36 MHz band. (The abbreviation MHz stands for megahertz, or 10 6 Hz, or 10 6 cycles per second. Other common abbreviations are Hz for 1 Hz, kHz for 10 3 Hz, and GHz for 10 9 Hz.) Each transponder actually transmits two channels of information, one vertically polarized and one horizontally polarized. There is an 8 MHz guard band between each band, and the vertical and horizontal channels are offset by 20 MHz. The transmission scheme for the 24 channels is illustrated in Figure 1 . The entire transmission band extends over 540 MHz, from 3 . 7 × 10 9 Hz to 4 . 24 × 10 9 Hz. The satellite receiver has two different microwave detectors, one for vertical and one for horizontal polarization, and a microwave tuner to tune into the microwave band of interest.

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, A first course in electrical and computer engineering. OpenStax CNX. Sep 14, 2009 Download for free at http://cnx.org/content/col10685/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'A first course in electrical and computer engineering' conversation and receive update notifications?

Ask