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We address deviations in the source bearing of natural pulsed extremely low frequency (ELF) radio signals (Q-bursts) in the Schumann resonance band. The model of smooth day – night non-uniformity is used. The observer is located at the Ukrainian Antarctic station "Akademik Vernadsky" (65.25° S and 64.25° W), and the source is positioned at the same meridian at latitudes of 20° S; 25° N, or 85° N. The equinox period is considered when the solar terminator line is coincident with a meridian. Thus, the source – observer meridian and the terminator meridian are separated by an angular distance varying with the local time of observer. The propagation parameters of ELF radio waves were computed using the full wave solution in the form of Riccati equation for the ambient day and ambient night profiles of mesosphere conductivity. The field spectra were found from the 2D telegraph equations (2DTE). Spectra of the source bearing and of the polarization coefficient were computed for different local times. The source bearing and the polarization coefficient do not exceed ±15° and ±0.35 correspondingly. The Q-bursts in the time domain were computed at the output of an example Schumann resonance receiver. Phasors of the Poynting vector were used for estimating the source bearing in the time domain. Maximum deviations in the source azimuth may reach ±4° directed toward to the midnight point. The eccentricity of the "elliptic" magnetic field phasor may reach 0.1. Impact of the day – night non-uniformity is comparable with that of the continuous Schumann resonance background. Therefore, terminator effect is detectable in records of extra-powerful Q-bursts exceeding the background noise by the factor of 10–20. • Realistic model of the Earth–ionosphere cavity with the day–night non-uniformity is used. • Propagation parameters of ELF radio waves were computed using the full wave solution in the form of Riccati equation. • Spectra of vertical electric and two orthogonal horizontal magnetic fields were found using 2D telegraph equations. • Observer was at 65.25°S and 64.25°W, and the source occupied the same meridian at latitudes 20°S; 25°N, or 85°N. • The equinox period was considered when the solar terminator is coincident with a meridian. • Spectra were computed of the source bearing and of polarization coefficient for different local time of observatory. • Deviation of the source bearing may reach ±15°, and of the polarization coefficient may reach the ±0.35 interval. • The Q-bursts were computed with account for the gain of an example Schumann resonance receiver. • Time domain phasors of horizontal Poynting vector were used for estimating the source bearing. • The time domain deviations may reach ±4°, and the Poynting vector tends to point to the midnight position. • Detection of terminator effect in the source bearing is possible for Q-bursts exceeding the background by a 10–20 factor. [ABSTRACT FROM AUTHOR]