This paper presents the first implementation on software defined radio nodes in the large scale testbed called CorteXlab of a radio link estimation technique based on OFDM transmissions. The purpose of this large scale testbed is to offer to the whole scientific community an open tool to test new techniques for multiuser , cooperative and cognitive radio networks in a controlled environment. As the experimentation room was defined in order to offer reproducible measurements, it is important to be able to characterize each radio link between all transceivers. Therefore, we present here the development of a channel sounder directly implemented on the software radio nodes.