diff --git a/Tools/AntennaTracker/AntennaTracker.pde b/Tools/AntennaTracker/AntennaTracker.pde
index 165dac503e..7476b43adb 100644
--- a/Tools/AntennaTracker/AntennaTracker.pde
+++ b/Tools/AntennaTracker/AntennaTracker.pde
@@ -108,6 +108,8 @@ static struct {
 
 static uint32_t start_time_ms;
 
+static bool usb_connected;
+
 ////////////////////////////////////////////////////////////////////////////////
 // prototypes
 void gcs_send_text_fmt(const prog_char_t *fmt, ...);
@@ -216,6 +218,7 @@ static const AP_Scheduler::Task scheduler_tasks[] PROGMEM = {
     { compass_accumulate,     1,   1500 },
     { barometer_accumulate,   1,    900 },
     { update_notify,          1,    100 },
+    { check_usb_mux,          5,    300 },
     { gcs_retry_deferred,     1,   1000 },
     { one_second_loop,       50,   3900 }
 };
diff --git a/Tools/AntennaTracker/system.pde b/Tools/AntennaTracker/system.pde
index 0fa7402b22..c70d45d84b 100644
--- a/Tools/AntennaTracker/system.pde
+++ b/Tools/AntennaTracker/system.pde
@@ -27,6 +27,11 @@ static void init_tracker()
     // more than 5ms remaining in your call to hal.scheduler->delay
     hal.scheduler->register_delay_callback(mavlink_delay_cb, 5);
 
+    // we start by assuming USB connected, as we initialed the serial
+    // port with SERIAL0_BAUD. check_usb_mux() fixes this if need be.    
+    usb_connected = true;
+    check_usb_mux();
+
     // we have a 2nd serial port for telemetry
     hal.uartC->begin(map_baudrate(g.serial1_baud, SERIAL1_BAUD),
                      128, SERIAL1_BUFSIZE);
@@ -235,3 +240,25 @@ static void set_mode(enum ControlMode mode)
     }
 }
 
+static void check_usb_mux(void)
+{
+    bool usb_check = hal.gpio->usb_connected();
+    if (usb_check == usb_connected) {
+        return;
+    }
+
+    // the user has switched to/from the telemetry port
+    usb_connected = usb_check;
+
+#if CONFIG_HAL_BOARD == HAL_BOARD_APM2
+    // the APM2 has a MUX setup where the first serial port switches
+    // between USB and a TTL serial connection. When on USB we use
+    // SERIAL0_BAUD, but when connected as a TTL serial port we run it
+    // at SERIAL1_BAUD.
+    if (usb_connected) {
+        hal.uartA->begin(SERIAL0_BAUD);
+    } else {
+        hal.uartA->begin(map_baudrate(g.serial1_baud, SERIAL1_BAUD));
+    }
+#endif
+}