  Radio Frequency Interference (RFI) is a growing concern in the radio
astronomy community. Single-dish telescopes are particularly susceptible to
RFI. Several methods have been developed to cope with RF-polluted environments,
based on flagging, excision, and real-time blanking, among others. All these
methods produce some degree of data loss or require assumptions to be made on
the astronomical signal. We report the development of a real-time, digital
adaptive filter implemented on a Field Programmable Gate Array (FPGA) capable
of processing 4096 spectral channels in a 1 GHz of instantaneous bandwidth. The
filter is able to cancel a broad range of interference signals and quickly
adapt to changes on the RFI source, minimizing the data loss without any
assumption on the astronomical or interfering signal properties. The speed of
convergence (for a decrease to a 1%) was measured to be 208.1 us for a
broadband noise-like RFI signal and 125.5 us for a multiple-carrier RFI signal
recorded at the FAST radio telescope.
