  Array-based, direct-sampling radio telescopes have computational and
communication requirements unsuited to conventional computer and cluster
architectures. Synchronization must be strictly maintained across a large
number of parallel data streams, from A/D conversion, through operations such
as beamforming, to dataset recording. FPGAs supporting multi-gigabit serial I/O
are ideally suited to this application. We describe a recently-constructed
radio telescope called ETA having all-sky observing capability for detecting
low frequency pulses from transient events such as gamma ray bursts and
primordial black hole explosions. Signals from 24 dipole antennas are processed
by a tiered arrangement of 28 commercial FPGA boards and 4 PCs with FPGA-based
data acquisition cards, connected with custom I/O adapter boards supporting
InfiniBand and LVDS physical links. ETA is designed for unattended operation,
allowing configuration and recording to be controlled remotely.
