The Relation of the Carrying Car to the Accuracy of Portable Field-Intensity-Measuring Equipment

The distortion of radio-frequency fields in the vicinity of automobiles is shown to be due to a secondary field resulting from eddy currents induced in the metal parts by the primary field. Theory and experiment demonstrate that the error of measurement caused by the presence of a metal-body car is independent of frequency within the broadcast band. It is shown that the distortion of the field changes with the position of the car, being greatest when the car is in line with the direction of the source and least when the length of the car is normal to the direction of the source. One method of equalizing this difference is pointed out. Measured field contours around three types of automobiles are illustrated.