$ echo ab | od -cx  # your method: 2-byte units in hex
0000000    a   b  \n                                                    
             6162    0a00                                               
0000003

$ echo ab | od -c -t xC  # my method: char-sized units in hex
0000000    a   b  \n                                                    
           61  62  0a                                                    
0000003