Rotating spiral waves have been observed in various excitable
media, including heart muscle, retinae, cultures of the slime mould
Dyctiostelium discoideum and chemical oscillators such as the
Belousov-Zhabotinsky (BZ) reaction. Under certain conditions the spiral
wave does not exhibit simple period rotation, but quasiperiodic (or
"compound") rotation, in which the spiral's origin (the tip) meanders.
Recent calculations have shown that highly meandering tip motion can
impose superstructures on spiral waves. Here we reproduce these patterns
experimentally, using the BZ reaction as the excitable medium. We induce
high tip meander by applying pulses of electric current  locally at the
tip. Image processing of the patterns reveals a spiral wave of larger
wavelength superimposed on the original wave, an effect that can be
described in terms of a Doppler shift in the original wave.