Abstract: The diagnostic test uses the effects of closed loop power control in order to measure the return loss of a receive antenna in a CDMA radio system. A standard CDMA call is established under closed loop power control by a mobile in a test unit. Using a switch matrix, the call is directed on the incident path of a receiving antenna. After a stabilization interval, the mobile phone in the test unit is queried for its transmit power level. The established call is then directed on the reflected path of the receiving antenna. After a stabilization interval, the mobile phone is again queried for its transmit power level. The difference between the previous incident transmit power level and the new increased transmit power level is the return loss of the antenna.