Apparent consequence of changing bands mid-stream in the cycle - these 20-meter signals were erroneously logged as 15 meters:
1638 -13 1.0 21.096042 1 KB1MVX EM73 27
1638 -16 0.5 21.096078 0 KN4ZXG FM16 37
1638 -11 0.6 21.096161 -2 KX4TD EM84 23