| System | Transmitter | Receiver | Signal |
|---|---|---|---|
| U.S. Mail | Letter writer | Addressee | Written letter |
| Radio | Radio station | Radio | Radio waves |
| Wi-fi | Controller or game | Television | Microwaves |
| Computer or printer | Computer | Printer | Electrical pulses |
| Conversation | Vocal cords & mouth | Ears | Sound waves |
| Sign language | Hands | Eyes | Sign language symbols |