Abstract: This invention relates to a radio transmitter having a power amplifier and a linearizer arrangement, for example Cartesian feedback, for compensating for non-linearity in the power amplifier. A training signal is applied to the amplifier (36) and the linearizer arrangement is adjusted during a training mode of operation. In one embodiment, a look-up table (23) is provided for storing predetermined operating condition adjustment parameters. According to an operating condition input (e.g. frequency, temperature) control means (21) select operating condition adjustment parameters during the training mode and adjust the training signal to compensate for loop gain variations during the training mode. Automatic gain control (26) may be provided in the amplifier loop for activation during at least a portion of the training mode of operation to maintain constant closed loop gain.