  Inductively coupled resonant circuits are affected by the so-called frequency
splitting phenomenon at short distances. In the area of power electronics,
tracking of one of the peak frequencies is state-of-the-art. In the data
transmission community, however, the frequency splitting effect is often
ignored. Particularly, modulation schemes have not yet been adapted to the
bifurcation phenomenon. We argue that binary frequency shift keying (2-ary FSK)
is a low-cost modulation scheme which well matches the double-peak voltage
transfer function $H(s)$, particularly when the quality factor $Q$ is large,
whereas most other modulation schemes suffer from the small bandwidths of the
peaks. Additionally we show that a rectified version of 2-ary FSK, coined
rectified FSK (RFSK), is even more attractive from output power and
implementation points of view. Analytical and numerical contributions include
the efficiency factor, the impulse response, and the bit error performance. A
low-cost incoherent receiver is proposed. Theoretical examinations are
supported by an experimental prototype.
