Radio telescopes produce enormous amounts of data. Many of them use GPU clusters to combine the digitized antenna signals, usually in real time. Achieving high data rates is challenging: the PCIe bandwidth of discrete GPUs is limited, and without RDMA, handling 200 or 400 Gb/s Ethernet packets with telescope data is difficult. The NVIDIA Grace Hopper is a novel, innovative system that eliminates the I/O bottleneck of traditional, discrete GPUs by using NVLink instead of PCIe. This opens the door to higher data rates, but faster hardware alone is not enough. In this paper, we combine hardware and software innovations to process Ethernet packets at no less than 1.2 Tb/s, a huge improvement over what was previously possible. We use the Data Plane Development Kit to minimize the receive overhead, and use a new feature that allows packet processing directly by the GPU. We demonstrate the data handling in a correlator application, analyze the performance, and show how to reduce the energy use. The presented innovations enable the use of GPUs for more powerful telescopes with much higher data rates. The results are also of interest to (GPU) applications from other application domains with high I/O demands, especially if RDMA is not available.