This report summarizes the results of a limited investigation to study the validity of existing standards used in frequency planning of broadcast services for the protection afforded by the characteristics of receiving aerials against interfering transmissions. Although internationally agreed standards have been provided by the CCIR, some aspects of these CCIR standards are ambiguous. An associated planning standard relating to assumptions about the variation of received signal with height of the receiving aerial above ground level is discussed in the Appendix to the Report.