Default RTL gain of 35 and parser catches negative shifts generated by invalid packets.

apps/uhd_modes.py

@@ -29,6 +29,7 @@ from string import split, join
 import air_modes
 import gnuradio.gr.gr_threading as _threading
 import csv
+from air_modes.modes_exceptions import *
 
 class top_block_runner(_threading.Thread):
     def __init__(self, tb):
@@ -87,7 +88,7 @@ class adsb_rx_block (gr.top_block):
 
         self.u.set_gain_mode(0) #manual gain mode
         if options.gain is None:
-            options.gain = 49
+            options.gain = 34
             
         self.u.set_gain(options.gain)
         print "Gain is %i" % self.u.get_gain()

python/modes_parse.py

@@ -77,9 +77,16 @@ class data_field:
   def get_bits(self, *args):
     startbit = args[0]
     num = args[1]
-    bits = (self.data \
+    try:
+      bits = (self.data \
         >> (self.get_numbits() - startbit - num + self.offset)) \
          & ((1 << num) - 1)
+    #the exception handler catches instances when you try to shift more than
+    #the number of bits. this can happen when a garbage packet gets through
+    #which reports itself as a short packet but of type long.
+    #TODO: should find more productive way to throw this out
+    except ValueError:
+      bits = 0
     return bits
 
 class bds09_reply(data_field):