Hi James and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, bear with us; re-confirm and post back with the complete model number of the radio.
Additionally, please provide further description of the "...K200 antenna receptacle..."
Appreciate the post back James.
Offhand, it would require an adapter to match the plug to the jack; something like the product shown HERE.
HERE is an adapter for 3.5MM down to 2.5MM