That appears to be an Antennas Direct DB8 (not the newer DB8E). The box contains a network that transforms the 300Ω impedance of antenna to the 75Ω impedance of the coax, and also interfaces the balanced antenna output with the unbalanced coax.
Contact Antennas Direct support:
http://www.antennasdirect.com/customer-service.html
FWIW, Though it's possible, the chances are low that the matching network has failed. Are there trees in the path of the antenna?