Low-power wireless link quality is known to be frequency- dependent because of multipath fading and other factors. We present a performance study of IEEE 802.15.4 radio links that quantifies and analyzes this frequency-specific performance in a clear-field outdoor environment. Using data from 16 channels on 240 links, we show that effect from channel selection on the average link is up to 4.89 dB, comparable with the effect from 38.7 C change in temperature. These results provide a performance baseline for other environments, as the diversity can be expected to further increase in environments with more obstacles and external interference.