Microwave transmission in the S Band are used in WiMAX, mobile telephony, air control and satellite communications. Such applications demand the use of wideband optical access networks. In this article, the impact of non-linearities of a fluorescent optical source (FFOS) is analyzed on the performance, at 560 nm, of Discrete-Multitone (DMT) transmissions, using the multicarrier signal-to-noise ratio (SNRmc) metric. The objective is to provide a model of SNRmc level curves based on empirical measurements by varying the bias current and the amplitude of the input signal in the optical source. The cartography was approximated by fitting ellipses, which allows us to find an approximate optimum point of operation for the setup.