It is shown in the paper that the chief factor limiting the application of the radiation method using horizontally polarized waves for the calibration of field-strength measuring sets to short radio waves is the difficulty encountered on longer wavelengths in preventing the radiation and reception of vertically polarized waves. This effect becomes more and more important with increase in wavelength and sets a practical upper wavelength limit to the radiation method of calibration at about 30 m. (frequency 10 Mc./s.).In order to assist in such calibrations, curves are given in the paper for the rapid computation at any wavelength up to 30 m. of the field-strength at a distance of 100 m. from any radiator of horizontally polarized waves.With the view of verifying these conclusions experimentally, a comparison was made of the radiation method and a laboratory method of calibrating a field-strength measuring set. The sensitivity of this measuring set, determined by the radiation method, was 4.8 μV per metre and 2.6 μV per metre at wavelengths of 8 m. and 20 m. (frequencies 37.5 and 15 Mc./s.) respectively. The corresponding sensitivities, found experimentally by the laboratory method, were 5.0 μV per metre and 2.5 μV per metre. The close agreement between the results obtained with the radiation and laboratory methods indicates that either may be used over the wave-band and investigated.