  We present an implementation of a channelizer (F-engine) running on a
Graphics Processing Unit (GPU). While not the first GPU implementation of a
channelizer, we have put significant effort into optimizing the implementation.
We are able to process four antennas each with 2 Gsample/s, 10-bit
dual-polarized input and 8-bit output, on a single commodity GPU. This fully
utilizes the available PCIe bandwidth of the GPU. The system is not as
optimized for a single high-bandwidth antenna, but handles 6.2 Gsample/s,
limited by single-core CPU performance.
