An apparatus for testing cellular base stations is provided. A base station tester is connected to a control link between the base station controller and the cellular base station to receive the fixed signal. The fixed link signal contains a voice channel and a control channel that may be selectively monitored by the base station tester. The base station tester is also connected to the radio frequency (RF) output of the cellular base station to receive the RF signal from the cellular base station. Both the RF signal and the fixed link signal are obtained in a non-invasive manner such that the cellular base station may remain in service during the testing process. By monitoring the fixed link directly, the base station tester may evaluate directly the reaction of the cellular base station with its RF signal to the commands received from the fixed link to perform parametric transmitter measurements. The base station tester may further compare the information received from the voice channel with the information contained in the RF signal to perform parametric receiver measurements.