By the present invention a calibration and/or correction of transmit signals in a communication system using Frequency Division Duplex has been disclosed, in particular a method of calibration of a transmit signal to be transmitted in a device simultaneously receiving and transmitting signals in the communication system, wherein the transmit signal and the receive signal are separated by a predetermined frequency band gap. A down-conversion of the transmit signal received in the receiving path to an intermediate frequency is performed, whereby the intermediate frequency corresponds to the frequency band gap reduced by the intermediate frequency of the receive signal. A correction signal is derived from the intermediate received transmit signal and used to calibrate the transmit signal such that non-linearity effects caused by power amplifiers in the transmit path are effectively reduced. The present invention provides the advantages of an improved and simplified architecture and simultaneously of a clearly improved quality of transmit signals.