Magnetic field due to instabilities in plasma is expected to be reflected in the conductive vessel wall. We evaluate the reflection effect in the Brazilian tokamak TCABR. The magnetic field due to the plasma is represented by a toroidal harmonic function in vacuum and the reflected field is written as a series of harmonic functions in vacuum, generated in the external region. The conclusion is that a signal originated in the plasma may be strongly deformed, close to the wall. Even far from the wall, around the plasma, the effect of the wall may still be considerable.