We present some results of investigation into obtaining ultraviolet radiation (UVR) at 0.271 mkm, by frequency summation of the copper-vapor laser radiation at 0.51 mkm and 0.578 mkm in a nonlinear DKDP crystal. Using an unstable optical resonator with the magnification factor M = 200 and spatial filter we have obtained the UVR of 0.75 W mean power at the conversion efficiency of 12%. In a low divergency beam the amplitudes of pulses at yellow and green lines came close and a time lag between them disappeared, that strongly favored the process of the UVR generation at the summed frequency.