The data available for calculating the ground-ray field are summarized and used as a basis for estimating the maximum range of communication for any given practical conditions. Particular attention is given to low-power (e.g. portable) transmitters with short aerials, and to the way in which the range of communication varies with wavelength and with the aerial used.Sky-wave communication is not treated, since it cannot normally be relied upon with the very low radiated powers (1 watt or less) primarily considered in the paper. Centimetre waves also are not covered: the range is here principally dependent upon the permissible aerial directivity, and many of the problems involved are of a some what different nature from those dealt with in the paper.Simplified field-strength formulae of general application are derived from the work of Burrows2and Norton.3Curves are given for the distance at which the field from a 1-watt transmitter falls to a given value for wavelengths from 0.5 m to 2000 m and aerial heights up to 15000 ft.An analysis of the ratio of power radiated to total power available gives the reduction in field from the transmitter when short aerials are used. The minimum field required at the receiver for intelligible communication is considered, and curves are then drawn for the range of communication.Practical rules are given for estimating ground-ray range for low-power sets.