  The Beamforming Elevated Array for COsmic Neutrinos (BEACON) is a planned
neutrino telescope designed to detect radio emission from upgoing air showers
generated by ultrahigh energy tau neutrino interactions in the Earth. This
detection mechanism provides a measurement of the tau flux of cosmic neutrinos.
We have installed an 8-channel prototype instrument at high elevation at
Barcroft Field Station, which has been running since 2018, and consists of 4
dual-polarized antennas sensitive between 30-80 MHz, whose signals are
filtered, amplified, digitized, and saved to disk using a custom data
acquisition system (DAQ). The BEACON prototype is at high elevation to maximize
effective volume and uses a directional beamforming trigger to improve
rejection of anthropogenic background noise at the trigger level. Here we
discuss the design, construction, and calibration of the BEACON prototype
instrument. We also discuss the radio frequency environment observed by the
instrument, and categorize the types of events seen by the instrument,
including a likely cosmic ray candidate event.
