This material was developed with funding from the
National Science Foundation under Grant # DUE 1601612
Controlling Digital Modulation
Click on the switches to set each bit as either 0 or 1 to see its possible modulation.
Changing the position of the first switch on the left generates a digital signal of 0 or 1. Notice that when a switch is in the OFF position, each of the carrier signals during that time period are not changed. Turning the switch to the ON position will result in the AM signal amplitude doubling, the FM signal doubles, and the PM signal shifts by 180 degrees. Use the switches to represent a digital signal that will be modulated using amplitude, frequency, and phase.
Frequency Modulation (FM)
Modulation mixes a low frequency signal with a sinusoid (a high frequency carrier signal) to produce a new signal. This new signal has certain benefits over an un-modulated signal.
Amplitude modulation modifies the carrier signal by changing its amplitude. The modulated result reflects the change in the carrier signal amplitude and represents data being carried.
Frequency modulation modifies the carrier signal by changing its frequency.
Digital modulation is used in both amplitude and frequency modulation. The modulated result can only have two states.
Click each item below for more information.
Amplitude Modulation (AM)
Where a one occurs, the frequency remains the same as the original carrier signal. When a zero occurs, the frequency doubles.
The frequency phase shifts by 180 degrees or reverses direction when a one occurs. When a zero occurs, the phase remains the same.
The digital signal used in modulation shows a higher amplitude when a one occurs and lower amplitude for a zero.
Digital signal modulation is the process of mixing a digital (discrete) signal with an analog carrier signal. The analog signal can then carry the digital information to analog receivers. Digital signal modulation is produced by a discrete signal being used to modify the amplitude, frequesncy or phase of the original analog signal.
< Click each number for more information.
Peak-to-Peak Amplitude is the change between peaks (highest amplitude value) and trough (lowest amplitude value, which can be negative).
The amplitude of a signal is the strength of the signal.
Click on each numbered circle to see the various definitions of amplitude.
Peak amplitude is used to measure the signal rise above and below a reference value.
Root Mean Square Amplitude (RMS)
The RMS amplitude is used in electrical engineering: the RMS is a mathematical quantity used to compare both alternating and director currents (or voltage).
Frequency is the number of signal cycles that occur in one second. A cycle is a complete sinusoid signal which starts at a reference point, completes a positive transition, completes a negative transition, and returns to the original reference point.
Frequency is the number of occurrences of a repeating signal pattern per unit of time. The period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example: if a person's heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second (60 seconds divided by 120 beats). Because the period and frequency are reciprocals, when frequency increases, the period decreases. If the frequency decreases, the period increases.
Phase is measured like a circle—between 0 and 360 degrees. If you travel one fourth of the circumference of the circle, you will complete 90 degrees; if you travel one half of the circumference of the circle, you will complete 180 degrees. Travelling the whole circle results in completing 360 degrees. Sine waves use the same concept to measure the completion of an entire wave cycle.
A complete cycle is 360 degrees of phase as shown in red. Phase difference, also called phase angle, is a number greater than -180, and less than or equal to +180. Leading phase refers to a wave that occurs ahead of another wave of the same frequency (the blue wave is 90 degrees ahead of the red wave and the green wave is 180 degrees ahead of the red wave). Lagging phase refers to a wave that occurs behind another wave of the same frequency.
The red wave lags the green wave by 180 degrees, and it lags the blue wave by 90 degrees.
Modulation is the modification of an electronic carrier signal to transmit information from one point to another. Transmission devices modulate a carrier signal and receiving devices demodulate the signal to extract the information carried. To understand modulation, you need to identify signal amplitude, frequency, and phase.