diff --git a/apps/modes_rx b/apps/modes_rx
index a999659..7db6e6a 100755
--- a/apps/modes_rx
+++ b/apps/modes_rx
@@ -55,7 +55,7 @@ class adsb_rx_block (gr.top_block):
     if options.filename is None and options.udp is None and not options.rtlsdr:
       #UHD source by default
       from gnuradio import uhd
-      self.u = uhd.single_usrp_source("", uhd.io_type_t.COMPLEX_FLOAT32, 1)
+      self.u = uhd.single_usrp_source(options.args, uhd.io_type_t.COMPLEX_FLOAT32, 1)
       time_spec = uhd.time_spec(0.0)
       self.u.set_time_now(time_spec)
 
@@ -81,7 +81,7 @@ class adsb_rx_block (gr.top_block):
       
     elif options.rtlsdr: #RTLSDR dongle
         import osmosdr
-        self.u = osmosdr.source_c()
+        self.u = osmosdr.source_c(options.args)
         self.u.set_sample_rate(2.4e6) #fixed for RTL dongles
         if not self.u.set_center_freq(options.freq):
             print "Failed to set initial frequency"
@@ -143,6 +143,8 @@ if __name__ == '__main__':
           help="select USRP Rx side A or B", metavar="SUBDEV")
   parser.add_option("-A", "--antenna", type="string",
           help="select which antenna to use on daughterboard")
+  parser.add_option("-D", "--args", type="string",
+          help="arguments to pass to UHD/RTL constructor", default="")
   parser.add_option("-f", "--freq", type="eng_float", default=1090e6,
                       help="set receive frequency in Hz [default=%default]", metavar="FREQ")
   parser.add_option("-g", "--gain", type="int", default=None,