Waveforms:

This section will provide you with some background on waveforms and on measuring waveforms. It is especially important that you understand how to measure waveforms. This is a skill that is not only important to this lab, but also to the T-1 Lab and in labs for other Telecommunications Courses.
• There are two types of alternating-current signals, which are also called waveforms:
• Periodic
• Non-periodic
_ Periodic signals, such as sine or triangle waves, behave in a uniform manner and repeat themselves over a given length of time. Each repetition of a repeating signal is called a period or a cycle.
_ Non-periodic signals, such as analog voice, behave in a non-uniform manner and do not repeat themselves over any given length of time.
Note: In this lab, we will only work with periodic signals.
• When working with AC signals, there are three properties of the signal that we are concerned with: amplitude, period and frequency.
• The amplitude of the wave is defined as the maximum magnitude of the wave. The amplitude is the vertical component of the signal and is measured in units of volts (V). Since we are dealing with an AC signal, the voltage will change over a period of time. The maximum voltage of a signal during its cycle is commonly referred to as the peak voltage (Vp).
• The amplitude can be measured from the reference line to the peak (Vp) or from peak-to-peak (Vpp). See Figure 1 below.

peak-to-peak amplitude peak or maximumamplitudereference point
Figure 1: Measuring Amplitude.


• With a periodic signal that is symmetrical (equi-distant above and below the reference point), the peak-to-peak voltage is equal to twice the peak voltage:
Vpp = 2 * Vp
• The period (T) of the signal is defined as the time it takes for a signal to complete one full cycle. The period is the horizontal component of the signal, measured in units of seconds (s). In Figure 2, the period of the signal is measured as 250 milliseconds (250.0 x 10-3s).

PERIOD one second250 msec250 msec250 msec250 msec
Figure 2: Measuring Period.


• The frequency (f) of the signal is defined as the rate at which a periodic signal repeats. It is usually measured in units of Hertz (Hz), where 1 Hz = 1 cycle per second.
• In Figure 4, above, you can see four(4) cycles occurring within one second; therefore, the signal has a frequency of 4 Hz.
• The frequency, f, of a wave is inversely related to its period (T):
f = 1 / T
• Example:
The period of the signal is 250 milliseconds, therefore the frequency of that signal is:
f = 1 / T f = 1 / 250 milliseconds f = 4 Hertz

Table of Scientific Prefixes
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Abbreviation Prefix_Name Factor
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T Tera 10^12
G Giga 10^9
M Mega 10^6
K Kilo 10^3
m milli 10^-3
μ micro 10^-6
n nano 10^-9
p pico 10^-12
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