Electrostatic radiation from a monopole antenna in a magnetoplasma is studied theoretically in the frequency range between the electron gyrofrequency and its second harmonic. The scalar potential created by a point source is calculated numerically using the least‐damped‐root approximation, which involves considering only two roots of the dispersion equation, corresponding to the oblique mode and to the cyclotron harmonic mode. The potential distribution can be understood as being due both to interference between these two modes and to diffraction of the cyclotron harmonic mode alone. Theoretical spatial distribution fit the experimental data. In particular, the theory confirms that cyclotron harmonic waves should be detectable in all directions from the source, as was observed experimentally. A good agreement with experimental data is shown by theoretical curves of constant phase and of constant amplitude. An approximate analytical model of the potential distribution is presented, and is compared with the numerical model and with experimental data. Finally, it is shown how such data can be interpreted to yield the electron density and temperature.