Tone transmission communicates values by encoding the duration of what?

• A. A digital packet containing time-stamped data.
• B. A radio frequency carrier with amplitude encoding the value.
• C. A continuous stream of binary bits conveying the measurement.
• D. A pure audible tone whose duration represents a measured value.

Answer: (D)

Tone transmission encodes the measured value by how long the tone lasts. The system sends a pure audible tone, and the receiver determines the value from the duration of that tone—the longer the tone, the higher the value, and the shorter the tone, the lower the value. This is different from sending a digital packet, modulating a radio carrier by amplitude, or streaming a continuous stream of binary bits, all of which convey information through structure, amplitude, or bit patterns rather than the duration of a tone. So the best description is a pure audible tone whose duration represents a measured value.