Paragraph 1 Definitions of expressions used in this Schedule

Voltage and e.m.f.

References to the voltage or e.m.f. of a sinewave are references to its effective or root mean square value.

Decibel

The term “decibel” (abbreviated db) expresses the logarithmic ratio of two voltages or e.m.f.'s. The ratio of two voltages V₁ and V₂ expressed in decibels is 20 times the logarithm to the base 10 of V₁/V₂ i.e. 20 log₁₀ V₁/V₂.

Applied Voltage

The voltage applied to the input terminals of the measuring apparatus.

Reference deflection

The deflection of the needle of the indicating meter of the valve-voltmeter to a mark at the middle of the scale of the meter.

Tuned frequency

The mid-frequency of the band of frequencies for which the measuring apparatus is tuned to accept the applied voltage.

Intermediate frequency

The mid-frequency of the band of frequencies for which the intermediate frequency amplifier of the measuring apparatus is tuned to accept the voltage applied to it.

Image frequency

The frequency, not being the tuned frequency, which combines with the fundamental frequency of the beating oscillator to produce the intermediate frequency.

Field-strength calibration constant

The number of decibels that must be added to the reading of the measuring apparatus, when a measurement of field-strength is made as prescribed, to give the value of field-strength in decibels above one microvolt per metre.