  The Spherical Proportional Counter is a novel type of radiation detector,
with a low energy threshold (typically below 100 eV) and good energy
resolution. This detector is being developed by the network NEWS, which
includes several applications. We can name between many others Dark Matter
searches, low level radon and neutron counting or low energy neutrino detection
from supernovas or nuclear reactors via neutrino-nucleus elastic scattering. In
this context, this works will present the characterization of a spherical
detector of 1 meter diameter using two argon-based mixtures (with methane and
isobutane) and for gas pressures between 50 and 1250 mbar. In each case, the
energy resolution shows its best value in a wide range of gains, limited by the
ballistic effect at low gains and by ion-backflow at high gains. Moreover, the
best energy resolution shows a degradation with pressure. These effects will be
discussed in terms of gas avalanche properties. Finally, the effect of an
electrical field corrector in the homogenity of the gain and the energy
threshold measured in our setup will be also discussed.
