DF Cyg: faint Minimum of the RVB-secondary period YYMMDD(UT) mag observer 980206.833 126 (T. Watanabe) 980210.844 <127 (T. Watanabe) 980306.791 <128 (T. Watanabe) 980307.787 136 (T. Watanabe) 980316.749 126 (T. Watanabe) 980411.749 128 (T. Watanabe) 980425.749 137 (T. Watanabe) 980428.673 137 (T. Watanabe) 980503.710 136 (T. Watanabe) 980522.758 136 (T. Watanabe) 980530.647 133 (T. Watanabe) 980615.610 137 (T. Watanabe) 980722.678 128 (T. Watanabe) 980729.899 128 (L. Kiss) 980822.699 135 (T. Watanabe) 980903.524 134 (T. Watanabe)