The impulse amplitude distributions (LADs) of impulsive noise received at a narrow-band receiver's input are theoretically derived by postulating physically motivated combinations of spatial distributions of sources and propagations. Good agreements are found between theoretical IADs and measured envelope crossing rate distributions (CRDs) for atmospheric radio noise. Derivation of envelope amplitude probability distributions (APDs) is considered for the input of the derived IADs. Particularly, if the input is represented only by a single power function of the amplitude, derived APDs are found to agree completely with a well known and important category of APDs.