diff --git a/gnss-converters.cabal b/gnss-converters.cabal
--- a/gnss-converters.cabal
+++ b/gnss-converters.cabal
@@ -1,5 +1,5 @@
 name:                  gnss-converters
-version:               0.1.4
+version:               0.1.5
 synopsis:              GNSS Converters.
 description:           Haskell bindings for GNSS converters.
 homepage:              http://github.com/swift-nav/gnss-converters
diff --git a/src/Data/RTCM3/SBP.hs b/src/Data/RTCM3/SBP.hs
--- a/src/Data/RTCM3/SBP.hs
+++ b/src/Data/RTCM3/SBP.hs
@@ -38,12 +38,12 @@
   t <- toGPSTime hdr
   return ObservationHeader
     { _observationHeader_t     = t
-    , _observationHeader_n_obs = fromIntegral $ hdr ^. gpsObservationHeader_n
+    , _observationHeader_n_obs = 0x10
     }
 
 toP :: GpsL1Observation -> GpsL1ExtObservation -> Word32
 toP l1 l1e = round $ p * 100 where
-  p = 0.02 * fromIntegral (l1 ^. gpsL1Observation_pseudorange) +
+  p = (0.02 :: Double) * fromIntegral (l1 ^. gpsL1Observation_pseudorange) +
       299792.458 * fromIntegral (l1e ^. gpsL1ExtObservation_ambiguity)
 
 toL :: GpsL1Observation -> GpsL1ExtObservation -> CarrierPhase
@@ -72,36 +72,38 @@
   , _gnssSignal_constellation = 0
   }
 
-fromObservation1002 :: Observation1002 -> PackedObsContent
-fromObservation1002 obs = PackedObsContent
-  { _packedObsContent_P    = toP l1 l1e
-  , _packedObsContent_L    = toL l1 l1e
-  , _packedObsContent_cn0  = toCn0 l1e
-  , _packedObsContent_lock = toLock l1
-  , _packedObsContent_sid  = toSid sat
-  } where
-    sat = obs ^. observation1002_sat
-    l1  = obs ^. observation1002_l1
-    l1e = obs ^. observation1002_l1e
+fromObservation1002 :: Observation1002 -> Maybe PackedObsContent
+fromObservation1002 obs =
+  if obs ^. observation1002_l1 ^. gpsL1Observation_code then Nothing else Just PackedObsContent
+    { _packedObsContent_P    = toP l1 l1e
+    , _packedObsContent_L    = toL l1 l1e
+    , _packedObsContent_cn0  = toCn0 l1e
+    , _packedObsContent_lock = toLock l1
+    , _packedObsContent_sid  = toSid sat
+    } where
+      sat = obs ^. observation1002_sat
+      l1  = obs ^. observation1002_l1
+      l1e = obs ^. observation1002_l1e
 
-fromObservation1004 :: Observation1004 -> PackedObsContent
-fromObservation1004 obs = PackedObsContent
-  { _packedObsContent_P    = toP l1 l1e
-  , _packedObsContent_L    = toL l1 l1e
-  , _packedObsContent_cn0  = toCn0 l1e
-  , _packedObsContent_lock = toLock l1
-  , _packedObsContent_sid  = toSid sat
-  }  where
-    sat = obs ^. observation1004_sat
-    l1  = obs ^. observation1004_l1
-    l1e = obs ^. observation1004_l1e
+fromObservation1004 :: Observation1004 -> Maybe PackedObsContent
+fromObservation1004 obs =
+  if obs ^. observation1004_l1 ^. gpsL1Observation_code then Nothing else Just PackedObsContent
+    { _packedObsContent_P    = toP l1 l1e
+    , _packedObsContent_L    = toL l1 l1e
+    , _packedObsContent_cn0  = toCn0 l1e
+    , _packedObsContent_lock = toLock l1
+    , _packedObsContent_sid  = toSid sat
+    }  where
+      sat = obs ^. observation1004_sat
+      l1  = obs ^. observation1004_l1
+      l1e = obs ^. observation1004_l1e
 
 fromMsg1002 :: MonadIO m => Msg1002 -> m MsgObs
 fromMsg1002 msg = do
   header <- fromGpsObservationHeader $ msg ^. msg1002_header
   return MsgObs
     { _msgObs_header = header
-    , _msgObs_obs    = map fromObservation1002 $ msg ^. msg1002_observations
+    , _msgObs_obs    = mapMaybe fromObservation1002 $ msg ^. msg1002_observations
     }
 
 fromMsg1004 :: MonadIO m => Msg1004 -> m MsgObs
@@ -109,7 +111,7 @@
   header <- fromGpsObservationHeader $ msg ^. msg1004_header
   return MsgObs
     { _msgObs_header = header
-    , _msgObs_obs    = map fromObservation1004 $ msg ^. msg1004_observations
+    , _msgObs_obs    = mapMaybe fromObservation1004 $ msg ^. msg1004_observations
     }
 
 fromMsg1005 :: MonadIO m => Msg1005 -> m MsgBasePosEcef
@@ -142,4 +144,4 @@
   (RTCM3Msg1006 msg _rtcm3) -> do
     msg' <- fromMsg1006 msg
     return $ Just $ SBPMsgBasePosEcef msg' $ toSBP msg' defaultSender
-  _rtcm3Msg -> return $ Nothing
+  _rtcm3Msg -> return Nothing