The representation of the Earth's magnetosphere as an MHD waveguide has prompted much recent speculation. In particular, the signatures associated with ULF pulsations sit well within the waveguide concept. We further explore the appositeness of the waveguide model by simulating data that a spacecraft would see when passing through a stimulated magnetospheric waveguide and by comparing the results with those obtained from a real spacecraft. We find that the waveguide results again compare favorably and can explain many features seen in the data. We also find that the magnetometer signature of the fast mode in a waveguide (unlike a cavity) does not have a regular oscillatory nature with constant period over a range of L shells. ¿ American Geophysical Union 1995