You need to figure out the connector on your antenna (Mine is N-Female and most are). Then you need a cable that goes from SMA Male to whatever your antenna connector needs (likely N-Male) in LMR400 at the length you need.

This is the cable I used https://www.amazon.com/dp/B00H9II8Q4/ref=cm_sw_r_cp_api_XOalBb6JQW91W