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Wireless LAN radio interfaces based on the IEEE 802.11a standard have lately found widespread use in many wireless applications. A key reason for this was that although the predecessor, IEEE 802.11b/g, had a poor channelization scheme, which resulted in strangling adjacent channel interference (ACI), 802.11a was widely believed to be ACI-free due to a better channelization combined with OFDM transmission. We show that this is not the case. ACI does exist in 802.11a, and we can quantify its magnitude and predict its results. For this, we present minor modifications of a simple model originally introduced by that allow us to calculate bounding values of the 802.11a ACI, which can be used in link budget calculations. Using a laboratory testbed, we verify the estimations of the model, performing experiments designed to isolate the affected 802.11 mechanisms. This isolation was enabled by not using the wireless medium, and emulating it over cables and attenuators. Our results show clear throughput degradation because of ACI in 802.11a, the magnitude of which depends on the interfering data rates, packet sizes, and utilization of the medium.