diff --git a/src/python/uhd_modes.py b/src/python/uhd_modes.py
index 20bcad3..5ce65e9 100755
--- a/src/python/uhd_modes.py
+++ b/src/python/uhd_modes.py
@@ -54,7 +54,7 @@ class adsb_rx_block (gr.top_block):
     self.args = args
 
     if options.filename is None:
-      self.u = uhd.single_usrp_source("", uhd.io_type_t.COMPLEX_FLOAT32)
+      self.u = uhd.single_usrp_source("", uhd.io_type_t.COMPLEX_FLOAT32, 1)
 
       #if(options.rx_subdev_spec is None):
        # options.rx_subdev_spec = ""