PBS
Signal Senders
Send a signal to let others know one's location. Scholars investigate how scientists track the movement of marine wildlife. They model the process by creating a custom sound that can be used to identify each group member as they walk by.
CK-12 Foundation
Ck 12: Physical Science: Electronic Signal
[Free Registration/Login may be required to access all resource tools.] Covers electronic signal, how an electric current can be used to send an electronic message, what analog and digital signals are, and the difference between them.