Data of the continuous monitoring of the sub-ionospheric signals in Petropavlovsk-Kamchatsky have been used to analyze nighttime variations in the amplitude and phase of mid-latitude JJY (40 kHz) signal during the main stage of strong and extreme geomagnetic storms over three solar cycles (2000–2024). The results show that for the total 54 geomagnetic storms, only 16 caused disturbances in the radio signal. The effect was found for those geomagnetic storms whose main stage was during the local night. There were 20 such cases in total. The amplitude anomalies of the JJY signal ranged from 3 to 27 dB, phase anomalies varied from 29° to 135°. No direct relationship was found between the strength of geomagnetic activity and the JJY signal anomaly. In 4 cases, when the main stage of magnetic storms was during the local day or during the movement of the solar terminator through the signal propagation path, an anomalous shift in the position of characteristic minima in the diurnal variation of sub-ionospheric signals at the moments of sunset or sunrise relative to their normal position was found. Minima shifted by 1–2 h towards increasing the duration of the nighttime.