 Double tuning, as compared to single tuning, has the effect of widening the bandwidth of the amplifier and steepening the skirt of the response. Tuning both sides of the transformer forms a pair of coupled resonators which is the source of the increased bandwidth. The gain of the amplifier is a function of the coupling coefficient, k, which is related to the mutual inductance, M, and the primary and secondary winding inductances, Lp and Ls respectively, by
