SRTM30
From PathlossWiki
SRTM30 Global Terrain Data
SRTM30 is a 30" digital elevation database. It covers most of the earth from the latitudes 60°north to 56° south. It can be considered as an upgrade for the GTOPO30 digital elevation database.
More information and differences between SRTM30 and GTOPO30 can be found in this PDF from the USGS: http://dds.cr.usgs.gov/srtm/version2_1/SRTM30/srtm30_documentation.pdf
The data can be downloaded from the following link: http://dds.cr.usgs.gov/srtm/version2_1/SRTM30/
Each file is contained in it's own directory. The files required by Pathloss 4 and 5 are the *.DEM and *.HDR.