We have measured the basic characteristics of low current diffuse discharges in argon for low
pressures. The data for the voltage current characteristics and negative differential resistance were
obtained together with the data for the frequency and for the damping coefficient of the induced
oscillations. These data were compared with the predictions of a simple analytic model of Phelps,
Petrović and Jelenković [A.V. Phelps, Z.Lj. Petrović and B.M. Jelenković, Phys. Rev. E 47,
2825 (1993)] and it was found that, while most observables may be represented correctly, there is a
systematic discrepancy between the predictions for frequency of induced oscillations based on the
data for transport coefficients from the literature and measurements. The basic idea of the present
work is thus to check the fundamental assumptions of the theory and to extend the application of the
experiment to study the transition to constrictions in order to initiate modifications of the theory to
cover the transition to the constricted regime. Very good agreement was found between the spatial
profiles of the electric field calculated from the model and the data obtained from the spatial
profiles of emission and these data may be extended to follow the transition to the constricted
regime and the development of the cathode sheath.