Which device provides a highly accurate reference frequency for calibration purposes?

• A. A well-known (standard) frequency used for transmitting certain messages.
• B. A device used to produce a highly accurate reference frequency.
• C. A device for accurately measuring frequency to within 1 Hz.
• D. A device used to generate wide-band random frequencies.

Answer: (B)

Having a highly accurate reference frequency lets calibration instruments compare their readings to a stable, known standard. A device designed to produce that reference frequency, a frequency standard or reference oscillator, provides a long-term, well-controlled signal with minimal drift. This is what calibration relies on: a traceable, repeatable frequency that remains constant over time and temperature, so other frequencies can be measured or adjusted against it.

The other descriptions point to things that don’t serve as the source of a stable reference. A standard frequency used for signaling is a known tone or channel frequency, not a device that generates a calibration reference. A device that measures frequency is a counter or meter, not a source. A generator of wide-band random frequencies creates noise or broad-spectrum output, not a stable reference.