Modulation signal calibration between modem and radio using loopback

A radio-frequency output signal having a specified characteristic is produced using a combination of a calibrated radio unit in which a calibration factor is stored and an uncalibrated modem unit. The calibration factor is input to the modem unit from the radio unit, and the modem outputs to the radio unit a signal of a nominal signal level determined in accordance with the calibration factor. An actual signal level of the signal is measured, and a gain factor within the modem unit is adjusted until the nominal signal level and the actual signal level are substantially equal. A wireless modem includes a calibrated radio unit and an uncalibrated modem unit coupled to the radio unit. A first signal path is provided from the modem unit to the radio unit, and a feedback signal path from the radio unit to the modem unit. The modem unit includes control circuitry for outputting across the first signal path a signal that is nominally of a desired signal level, and for adjusting a nominal signal level of the signal in accordance with information received across the feedback signal path.