This paper presents a comparative study between the oblique sounding results, theInternational Telecommunication Union Rec533 HF prediction model, and the vertical sounding results of atransequatorial long haul link. The long haul link is a 12,760 km link between the Spanish Antarctic Station,SAS, located in the Livingston Island and the Ebro Observatory (OE) in Spain. The data were collected duringthree consecutive surveys (2009/2010, 2010/2011, and 2011/2012). The ionospheric channel from the SAS tothe OE is studied in terms of frequency availability as function of time using the measurements of an obliqueincidence sounder (OIS) and measurements of several vertical incidence sounding stations (VIS) placed nearthe estimated radiopropagation path. The results obtained show promising correlations between VIS andOIS measurements and led us to think that the frequency of largest availability for this particular long haulradio link can be estimated from the VIS sounding measurements.