A supersonic jet operated at an off-design condition supports a standing wave pattern of alternating compression and expansion waves, often called shock-cells. The interaction of turbulence with the shock-cells leads to an additional source of broadband noise that is preferentially radiated upstream, i.e. towards the engine. In commercial aircraft this condition occurs in the fan stream at the cruise-climb condition and adversely impacts passenger comfort in the forward cabin section. In military aircraft the extra acoustic loading on the aft structures leads to reduced life cycle times. An unheated jet with a design Mach number of 1.95 is studied at on-and off-design conditions; for the latter case the underexpanded jet has a fully expanded Mach number of 2.2. The near-fields of the jets are studied with respect to their mean, fluctuation, and spectral characterizations. It is observed that the shear layers of the off-design jet merge one diameter downstream of the on-design jet with a slight reduction in the peak level of velocity fluctuation. The spectral content of the velocity and pressure field, inferred from axial two-point measurements, of both jets is similar. The underexpanded jet differs, however, in that it supports Mach wave radiation stemming from supersonically-convecting instability waves. It is observed that the Mach waves significantly contribute to the near-field pressure.