  We present a concept, developed at the National Astronomy and Ionosphere
Center (NAIC) at Arecibo, Puerto Rico, for active suppression of Global
Positioning System (GPS) signals in the 305 m dish radio receiver path prior to
backend processing. The subsystem does not require an auxiliary antenna and is
intended for easy integration with radio telescope systems with a goal of being
a turnkey addition to virtually any facility. Working with actual sampled
signal data, we have focused on the detection and cancellation of the GPS L3
signal at 1381.05 MHz which, during periodic test modes and particularly during
system-wide tests, interfere with observations of objects in a range of
redshifts that includes the Coma supercluster, for example. This signal can
dynamically change modulation modes and our scheme is capable of detecting
these changes and applying cancellation or sending a blanking signal, as
appropriate. The subsystem can also be adapted to GPS L1 (1575.42 MHz), L2C
(1227.6 MHz), and others. A follow-up is underway to develop a prototype to
deploy and evaluate at NAIC.
