... About ATNF overview . ... These are commonly called ``standing waves'' by radio spectroscopists. ... Thus, the path delay corresponds directly to the number of cycles of standing wave across the spectral band. ... As well as varying in amplitude, standing waves can drift in phase with time, causing them to fail to subtract exactly when the simpler forms of passband calibration are applied. ... Phase drift of an n harmonic standing wave is described by watching the phase term from vary with time. ...