We suggest new decoding techniques for diversity channels employing space time codes (STC) when the channel coefficients are unknown to both transmitter and receiver. Most of the existing decoders for unknown diversity channels employ training sequence in order to estimate the channel. These decoders use the estimates of the channel coefficients in order to perform maximum likelihood (ML) decoding. We suggest an efficient implementation of the generalized likelihood ratio test (GLRT) algorithm that improves the performance with only slight increase in complexity. We also suggest an energy weighted decoder (EWD) that shows additional improvement without further increase in the computational complexity.