What is receiving directivity factor (RDF)?

The Receiving Directivity Factor (RDF) is a performance metric primarily used to evaluate how well a receiving antenna rejects omnidirectional noise. It is defined as the antenna's peak forward gain compared to its average gain across the entire hemisphere around and above the antenna. This measurement is especially valuable for low-band DXers (such as on 160m or 80m) because atmospheric noise typically arrives from all angles via skywave. By comparing the main lobe's gain to the average gain over the whole sky, RDF provides a highly accurate representation of how much an antenna will improve your signal-to-noise ratio (SNR). A higher RDF value indicates superior overall noise rejection. The incorrect options describe other common antenna metrics. Forward gain compared to the reverse direction is the 'Front-to-Back ratio'. Relative directivity compared to an isotropic radiator or a dipole refers to standard gain measurements expressed as 'dBi' or 'dBd', respectively.