You can use a quarter-wave impedance transformer to counter impedance mismatch from 50 ohm to 73 or 75 ohm. i.e. (73 or 75)/Z = Z/50 where Z is characteristics the impedance of the quarter-wave length line in between.
Another problem is that a dipole is balanced but usually a feed from coaxial cable isn't, so you will need a transformer that is also a Balun - look up antenna baluns.
Current can flow down the outside of a coaxial cable, causing radiation you don't want and reducing radiation from the dipole arm it is joined to. A balun stops this.