how to choose the balun for measuring?

I have a down-convert mixer, rf frequency is 2.4ghz, lo frequency is 2.39ghz, if frequency is 10mhz. Can you tell me how to choose the balun for measuring? where can I buy them from?
thanks!

I don't know how to choose it but you can find many types of baluns from Mini-circuits. They have many models which can work at high frequencies like yours.