In this work we demonstrate the use of a dual antenna receiver that employs a receiver-autonomous angle-ofarrival spoofing countermeasure. This defense is conjectured to be effective against all but the most sophisticated spoofing attempts. The technique is based on observation of L1 carrier differences between multiple antennas referenced to a common oscillator. We first employ a moderately sophisticated spoofer to "fool" a single-antenna civil receiver. We then deploy the same attack after augmenting the receiver with an additional antenna and with receiver-autonomous spoofdetection software. The work discusses the experimental results together with various issues related to sensitivity, probability of false alarm, impact of carrier multipath, line-bias-calibration, and physical setup and security. We suggest that this work is important to the community as it provides experimental validation of a low-cost technique for receiver-autonomous spoofing detection. Furthermore, the technique, when combined with physical security of the antenna installation, provides a strong defense against even a sophisticated attack. The receiver employed is an L1-only civil GPS receiver with multiple antenna capability. The GPS chipset employed is the venerable GP2015/GP2021 that has been freely available for over a decade. As such, this receiver is representative of many civil receivers in use today for a variety of applications. Multiple antennas are enabled either through multiple independent RF front ends and correlators or via antenna multiplexing into a single RF front end and correlator bank.