The techniques of superimposing the family of transmission curves on ionograms has been used to 

estimate the maximum usable frequencies (MUFs) for HF links for 100, 400 and 800 km skip 

distances at different hours of the day. This method of estimation is more suitable for short earth 

distances of 400 km. Optimum working frequency range of 5-9 MHz, 6-9.35 MHz and 8-12.43 

MHz may be suitable for radio communication within the South and West African regions.