In tone transmission, which feature encodes the measurement value?

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

Answer: (C)

In tone transmission, the measurement value is carried by how long the tone lasts. A fixed-frequency, pure audible tone is produced, and the duration of that tone encodes the value—longer tones represent larger measurements. The receiver measures the time length to recover the value. This differs from amplitude-based encoding (where the value would be shown by signal strength), digital packets with time-stamped data (which would convey data as structured digital messages), or a continuous stream of binary bits (which transmits a sequence of 0s and 1s rather than a single tone’s duration). So the duration of the pure tone is the mechanism that encodes the measurement.