|  | 4.1 |
| Background for Studying Frequency-Based Cable Testing
|  | 4.1.5 |
| Viewing signals in time and frequency
One of the most important facts of the information age is that data symbolizing characters, words, pictures, video, or music can be represented electrically by voltage patterns on wires and in electronic devices. The data represented by these voltage patterns can be converted to light waves or radio waves, and then back to voltage waves. Consider the example of an analog telephone. The sound waves of the caller’s voice enter a microphone in the telephone. The microphone converts the patterns of sound energy into voltage patterns of electrical energy that represent the voice. If the voltage patterns were graphed over time, the distinct patterns representing the voice would be displayed. An oscilloscope is an important electronic device used to view electrical signals such as voltage waves and pulses. The x-axis on the display represents time, and the y-axis represents voltage or current. There are usually two y-axis inputs, so two waves can be observed and measured at the same time. Analyzing signals using an oscilloscope is called time-domain analysis, because the x-axis or domain of the mathematical function represents time. Engineers also use frequency-domain analysis to study signals. In frequency-domain analysis, the x-axis represents frequency. An electronic device called a spectrum analyzer creates graphs for frequency-domain analysis. Experiment with this graphic by adding several signals, and try to predict what the output will look like on both the oscilloscope and the spectrum analyzer. Electromagnetic signals use different frequencies for transmission so that different signals do not interfere with each other. Frequency modulation (FM) radio signals use frequencies that are different from television or satellite signals. When listeners change the station on a radio, they are changing the frequency that the radio is receiving.
Web Links
Time and frequency relationship http://www.see.ed.ac.uk/~dil/ed-only/ demos/doc/demonstrations/ node3.html