In this paper we present the first field measurements taken using a new approach proposed in [1] for measuring link impairments in 802.11 WLANs. This uses a sender-side MAC/PHY cross-layer technique that can be implemented on standard hardware and is able to explicitly classify lost transmission opportunities into noise-related losses, collision induced losses, hidden-node losses and to distinguish among these different types of impairments on a per-link basis. We show that potential benefits arising from the availability of accurate and reliable data are considerable.