I key the KPA500 and Titan in parallel, but only the one that gets RF transmits. :) I can do that because the two amps use the same keying logic and the amp key line feeds a transistor. 73, Jim K9YC On Sat,10/22/2016 5:28 PM, john at kk9a.com wrote: > How do you control which amp's relay engages during TX?