Part 2 Method of measurement

With the aerial and feeder disconnected from the receiver of the measuring apparatus and the I.F. attenuator set at maximum loss, the zero control of the valve-voltmeter shall be adjusted to bring the needle of the indicating meter to the zero mark.

The receiver shall be tuned to the frequency, as indicated by the main tuning dial calibrations, at which it is desired to test, and its gain shall be set to that used when the measuring apparatus was calibrated.

The feeder and a dipole aerial of length approximating as closely as practicable to that used for the calibration of the measuring apparatus shall be connected to the receiver. The aerial may be set vertically or horizontally or in any intermediate position, as desired for the test. The R.F. amplifier tuning of the receiver shall be trimmed to give maximum deflection of the meter needle.

The attenuators shall then be adjusted to bring the meter needle to the reference deflection mark; the R.F. attenuator being adjusted so that the I.F. attenuator is set to the lowest possible value in excess of 10db.

The field-strength in decibels above 1 microvolt per metre will be given by the sum of the readings of the two attenuators plus the field-strength calibration constant appropriate to the frequency at which the measurement is being made. If this value is X decibels, the field-strength in microvolts per metre is given by the antilog to the base 10 of X/20