Abstract: One embodiment of the invention includes a method for testing the performance of a Global System for Mobile Communications (GSM) transmitter. The output of the GSM transmitter is converted to a digital signal. A power spectrum is estimated for the GSM transmitter according to the digital signal via a modified periodogram algorithm. A phase trajectory of the digital signal is determined, and an ideal phase signal is determined from the determined phase trajectory. A phase trajectory error is calculated from the determined phase trajectory and the determined ideal phase signal. A tested device may be considered compliant if the abovementioned phase error and spectral mask meet specific defined criteria, and fails the test if either of these does not meet the predefined limits. The present invention is targeted at reducing the test time and test equipment traditionally associated with the implementation of these tests.