In this work we study and demonstrate the performance of a Radio Frequency Interference detection algorithm that is applicable to fully polarized Earth Observation radiometers. The proposed Polarimetric Cross Frequency algorithm is based on analysis of spectral deviation of the 3 rd and 4 th Stokes parameters calculated form the dual polarized input of a radiometer. We define the new algorithm, simulate its performance, compare it with other commonly used detection algorithms, and perform a demonstration with electronics that is designed against space radiometer requirements. The results of the work demonstrate that the detection performance of the proposed algorithm is better than reference algorithms in optimal conditions, however, it has weaknesses for certain signals. Therefore, in future systems our recommendation is to combine the proposed algorithm with other RFI detection algorithms.