[en] The effect of an electron beam on the output signal of a diamagnetic loop, used in beam-plasma heating experiments, is studied by examining the diffusion of a magnetic field pulse through a cylindrically symmetric plasma column. The source of the magnetic field pulse in the calculations is a thin rotating E layer which has a trapezoidal shape in time. Exact analytical expressions are obtained for the electric and magnetic fields and for the integrated output of a diamagnetic loop placed outside the plasma column. It is shown that only for low plasma conductivity does the diamagnetic signal at all resemble the shape of the beam current pulse. The results are not sensitive to the shape of the beam current pulse