The Ground Based Augmentation System (GBAS) is being studied as a potential means to provide Category II/III precision approach operations. The current technology, the Instrumental Landing System (ILS) is expensive to maintain and suffers from multipath effects which inhibit capacity in all - weather conditions. The GBAS Approach Service Types (GASTs) have been define d to apply to the various levels of vertically guided approach for which up to GAST C relating to Category I precision approach have been standardized. GAST D is under development to support Category II/III precision approaches using the L1 C/A signal of t he GPS constellation. A GAST F concept is being developed within the SESAR framework on the basis of a multi - constellation (GPS and GALILEO) multi - frequency environment (L1/L5 and E1/E5a). In order to assess which processing models are to be selected for t he GAST F solution, the error models for the new signals must be developed taking into account the impact of the antenna and receiver. This paper presents the analysis of the noise and multipath characterisation using real measurements taken at an experimental ground station