Experiments were conducted during four days in January and February 2001 at Tucson AZ, to measure the performance of an optical wireless link between two telescopes 8.7 km apart. The transmission rate was OC-3 (155 Mbps) and the maximum total radiated power was 29 dBm. Extreme fluctuations in the received 1550-nm beam were observed, and these occasionally caused error bursts. The error bursts had frequencies (a maximum of 12 per hour) and durations (mostly < 1 sec.) That were low enough to permit data transmission, e.g. via Ethernet TCP/IP. Fluctuations in the power of the 1550-nm received beam were positively correlated with variations in the elevation centroid. No correlations with meteorological measurements were found.