This paper focuses on two different signal combining and detection methods for multi-antenna spectrum sensing in cognitive radio networks. These methods were previously introduced, and their performances are analyzed in the presence of additive white Gaussian noise (AWGN). Noting the severe fading conditions that may be encountered in cognitive radio networks, considering solely AWGN as channel impairment might not be realistic. Moreover the SNR gain obtained by receiver diversity using multiple antennas at the receiver may well be different than the single antenna case when Rayleigh fading is added to the channel model. Therefore, this paper evaluates the combining and detection methods in the presence of Rayleigh fading channel conditions and concludes that evaluating multi-antenna spectrum detection methods and algorithms with AWGN channels does not provide an accurate indication about their performances. As expected equal gain combining (EGC) method, which gives the best performance for the AWGN case, gives the worst performance with uncorrelated Rayleigh fading channels. Thus, we conclude that the performance comparison of the combining and detection algorithms may differ with different channel conditions.