Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Radio Waves
Name: N/A
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: 1991 


Question:
Could you explain modulation as it relates to radio waves and what is a radio carrier signal? This questions from a 6th grade sc.



Replies:
Hold up a flashlight, turn it on, and point it at the blackboard. The light that you see is a "carrier signal", "carrier beam", or whatever. Now turn the light on and off a few times. You are "modulating" the carrier beam when you do this. Navy ships at sea "talk" to each other with light signals using the method I described. Radio waves are "kinds" of light beams.

Jack L. Uretsky


Hi Adam-- Here is another analogy. Suppose someone is singing a single note for a length of time, but sometimes sings it softer and sometimes louder -- that is, the pitch (frequency) does not change over time, but the volume (amplitude) does. The single note corresponds to the carrier wave in AM (amplitude modulation), and its loudness vs. time corresponds to the signal conveyed by the carrier wave. If you plotted a graph of the wave, the signal would form a sort of "envelope" for the high-frequency carrier. In this way a complex signal can be carried by a simple wave. The same analogy can be used for FM (frequency modulation). Now imagine that the singer sings a note (say, with constant loudness, though this is not important) which does not quite remain at a single pitch; it varies some, but not too much, from a "central" pitch. The central pitch corres- ponds to the carrier, and the manner in which the wave deviates from the central pitch conveys the signal. If you plotted a graph of the wave, it would look much like a regular sine wave, except that the frequency would not be constant: in some places the wave would look slightly "scrunched" and in other places slightly "stretched". In both cases, you tune your radio to the carrier frequency.

Rcwinther



Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory