During the last decade, several land mobile communication networks have been developed based on full satellite solutions such as Globalstar or Iridium systems or on huge terrestrial networks such as GSM for example. Deploying new terrestrial networks or new satellite constellations for new telecommunication or broadcast mobile systems on very large areas would be so expensive that another solution is now often considered: hybrid systems with a terrestrial segment to cover high-density built-up areas and a satellite segment to bring services to the largest part of coverage area. In the framework of Satellite Digital Multimedia Broadcasting CNES project, such a hybrid mobile broadcast system was studied, in particular air interface performances. This performance assessment required a good knowledge of the hybrid single frequency network (SFN) propagation channel including a geostationary satellite and terrestrial gap fillers. The requirement for an exhaustive characterization of the hybrid SFN propagation channel involved the development of a specific channel sounding solution. Moreover, mobile telecommunication systems recently developed use spatial diversity techniques to take benefit from multipath spatial decorrelation in particular. The measurement of diversity gains in actual conditions can provide information very helpful for network deployment and air interface design. The CNES channel sounder enables to carry out such diversity measurements using only propagation data. This paper presents this channel sounder developed and used to measure the SFN radio propagation channel with four transmitters in spatial diversity configuration.