Abstract: In a Doppler VOR, the phase of the carrier wave of the carrier signal must lie symmetrically between the phases of the carrier waves of the sideband signals. To monitor these phase relationships, the carrier signal received by the sideband antennas (1) is applied to two mixers (14, 15) which are also fed with fractional signals of the upper and lower sidebands, respectively. The mixer output signals are applied to a phase comparator (16) whose output signal has a predetermined value corresponding to the prescribed phase relationships. The output signal of the phase comparator (16) is compared with a reference value in a monitoring facility (19).