diff --git a/cubesatsim/cubesatsim.ino b/cubesatsim/cubesatsim.ino
index cbb33453..c80d3e83 100644
--- a/cubesatsim/cubesatsim.ino
+++ b/cubesatsim/cubesatsim.ino
@@ -199,8 +199,9 @@ void setup() {
 	
 // setup radio depending on mode 
   config_radio();	
-	
-  start_isr();	
+  
+  if ((mode == BPSK) || (mode = FSK))	// only start ISR if FSK or BPSK mode
+    start_isr();	
 	
 ///  start_button_isr();