diff --git a/grc/hamnet70_demod_sc16qam.grc b/grc/hamnet70_demod_sc16qam.grc
index 963163f..5e9ddc3 100644
--- a/grc/hamnet70_demod_sc16qam.grc
+++ b/grc/hamnet70_demod_sc16qam.grc
@@ -113,7 +113,7 @@
     </param>
     <param>
       <key>value</key>
-      <value>[-0.08129028727943922, 0.5175310057290967, 0.7722893511238401, 0.1148018601746867, -0.722064124169458, -1.070325845435683, -0.7576079426568051, 0.18721137317967265, 0.8082354458186894, 0.16551431338345055, -0.8230511120132068, -0.9163786999175855, -0.6117803225418995, -0.6700353783249773, -0.769552358580221, -0.6553850013523769, -0.6616647090898005, -0.8642448711195908, -0.7657756901919124, -0.005797463799976558, 0.7988382349769702, 0.8294065542326889, 0.5908028280454155, 0.8256875067745597, 0.8146188978481508, -0.020634460059635405, -0.7697984549491852, -0.84444995115828, -0.7024762029888817, -0.6198196615385398, -0.6740683648840808, -0.8779717344643397, -0.7348420982832689, -0.03555345192059069, 0.6875748913521815, 1.05704028958943, 0.7936348650142598, -0.227788685490792, -0.8526208790280765, -0.019986388839869088, 0.8865006263699879, 0.22076477443065975, -0.8950135086547415, -0.8716653140660505, -0.5246199864711176, -0.8766401386744519, -0.8820374094504108, 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0.6889211336769204, 1.0570456723676904, 0.7725709448929612, -0.19590212486821, -0.7819571569662832, -0.19423766644757734, 0.7581363822306396, 1.0728178251588376, 0.6914413142827484, -0.0559215883795015, -0.714231805919135, -0.8810186116706932, -0.6976008989464094, -0.589776170839254, -0.7080987303190418, -0.8686370449617289, -0.7125582538956461, -0.0700815846806227, 0.7167712215345482, 1.04915692525072, 0.6815083449957776, -0.02120733959403598, -0.642439898181621, -1.0597993466297206, -0.8237039100427359, 0.265065657431864, 0.856492446785688, -0.022162936727173486, -0.8378600476158674, -0.24202708087827066, 0.7661621476781921, 1.110851446807837, 0.7334782497375953, -0.19604083328889133, -0.7767874366303583, -0.19960608098306046, 0.7442419567519329, 1.1021390478953919, 0.7621718117508358, -0.2279706381391869, -0.8566075585134577, -0.014523950412114933, 0.8956878607912002, 0.2031847194823793, -0.8590960372868359, -0.9037640628156428, -0.6384354626902238, -0.6418468961629767, -0.6972905655659191, -0.8295081610344438, -0.75336030166678, -0.06371099534624729, 0.7469059588768265, 1.0091981479043493, 0.6892638352155233, 0.010433271730807492, -0.6990168570572781, -1.0195483817807387, -0.7245281591204413, 0.04940571217794372, 0.7380066957315401, 0.8611504776216674, 0.6772851899539332, 0.6365704309810768, 0.7161466474566263, 0.7855407885789869, 0.7268081345517742]</value>
+      <value>[0.035200381981188585, -0.34360279992652465, -0.7702725545574488, -0.7514494201876957, -0.6180034257525113, -0.845293778142639, -0.8013100763973725, 0.02074196657698465, 0.7732896551369288, 0.8399273364853098, 0.6974609394650995, 0.6307845193394893, 0.6517225693490792, 0.9004944717744877, 0.8124064814015849, -0.13757272543393367, -0.8375982801688345, -0.1719770280750406, 0.8496311903340008, 0.8831734587868336, 0.5447636666148317, 0.8412491055083767, 0.9054304411628837, -0.20201107667255752, -0.9406643207806581, 0.07184505983158077, 0.9414391475341005, 0.011578565080478609, -0.8815750011446698, -0.21645478605592675, 0.766762188886342, 1.0847502726821747, 0.7752894014479472, -0.22710317249237202, -0.8604151959503216, -0.010399078575805016, 0.8649300255518592, 0.24398016907265654, -0.7924702999088836, -1.083492018379925, -0.7290615421938923, 0.16354614958403854, 0.8156248004282852, 0.18038436552396372, -0.8442378587424297, -0.9067805134008871, -0.6020919616494961, 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0.851224965829912, 0.24967571680920805, -0.8122031738057045, -1.0574682990166844, -0.673299364046149, 0.019811927933146033, 0.7410749549819731, 0.8857380628373264, 0.6415949766534641, 0.6582416981884681, 0.7555724120494922, 0.6921295453468757, 0.7144798336027072, 0.7047461986909813, 0.6250476712685042, 0.8661669537552367, 0.8661028461219289, -0.17264914475477205, -0.9344748757576697, 0.03439628507815546, 0.9840719987526741, -0.008466539345606663, -1.0016471953988, 0.01242631720849098, 0.9737314119338659, 0.02455307965144965, -0.8967104702099666, -0.2143522567715812, 0.7858007598470412, 1.0624611311909968, 0.7426785918051497, -0.15774961462599568, -0.8279294009540383, -0.17229789821312474, 0.8652664425075851, 0.8662273823025605, 0.5590477716402569, 0.8341559959035253, 0.8139278925822135, -0.029024253895756157, -0.7623559815429292, -0.8447133998767246, -0.6984310237730235, -0.6245234953113089, -0.6816534792530835, -0.8646862115564203, -0.7549571535000329, -0.017336798137493458, 0.7694610505757153, 0.882866129261439, 0.6356607559753149, 0.6669293402573881, 0.7795334312839456, 0.6473617994478603, 0.6480576551043754, 0.8887236829419612, 0.7332296029830532, 0.027187674856545392, -0.6837305916214288, -1.0527785773370186, -0.7820826116109263, 0.20150877848919396, 0.8152374213260799, 0.1418663296393665, -0.8108012787894103, -0.9055260931467441, -0.6516362985606257, -0.6260508995798809, -0.68247701435131, -0.8708513732480414, -0.8161341850171459, 0.11270032228618641, 0.8732012542062941, 0.15680791236046623, -0.8812258055043216, -0.832221324113779, -0.5765992232534259, -0.8479730845709736, -0.7611781817154223, -0.026670997819749645, 0.6843918258094186, 1.052419990826963, 0.7769419203312972, -0.19555315688196845, -0.782314385413117, -0.19550736335698912, 0.7592853818271842, 1.0727510699191427, 0.6728900627806644, -0.02508867968258595, -0.6549270257341537, -1.0424757066879482, -0.8202559047321292, 0.24290898801652638, 0.8959743145730159, -0.053026935608910135, -0.9369352031589485, -0.03528056783095917, 0.9021865241112244, 0.21643291441098902, -0.7879201541062689, -1.0602974234731453, -0.7792133448341945, 0.20677012657032184, 0.9055243843417551, -0.029258299378920882, -0.9519243541850811, -0.042166621295676526, 0.9057460776608539, 0.22061379475050927, -0.8000182184093458, -1.047072354987996, -0.7235115460211217, 0.09347242017628993, 0.7896875691824797]</value>
     </param>
   </block>
   <block>
@@ -375,7 +375,7 @@
     </param>
     <param>
       <key>value</key>
-      <value>[1, -1, -1, 1, -1, -1, -1, -1, -1, 1, 1, 1, -1, -1, -1, -1, 1, 1, -1, 1, -1, -1, -1, 1, -1, 1, 1, 1, -1, 1, 1, -1, -1, -1, 1, 1, -1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, 1, -1, 1, -1, 1, 1, -1, 1, -1, 1, -1, -1, -1, -1, -1, 1, -1, 1, -1, 1, -1, -1, -1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, 1, -1, 1, 1, -1, 1, 1, -1, -1, -1, 1, -1, -1, -1, 1, 1, -1, 1, 1, -1, -1, -1, -1, 1, 1, -1, -1, 1, -1, 1, 1, -1, 1, 1, -1, 1, -1, -1, -1, -1, 1, 1, -1, -1, 1, 1, 1, 1]</value>
+      <value>[-1, -1, -1,  1,  1,  1,  1, -1,  1,  1,  1, -1,  1, -1,  1,  1, -1, 1, -1, -1,  1, -1, -1, -1, -1, -1, -1,  1, -1,  1, -1,  1, -1,  1, 1, -1,  1, -1, -1, -1,  1,  1,  1, -1, -1,  1,  1, -1, -1,  1, -1, 1,  1,  1, -1,  1,  1, -1,  1,  1, -1, -1, -1, -1,  1, -1, -1,  1, 1, -1,  1, -1, -1,  1,  1,  1,  1,  1,  1, -1,  1, -1,  1, -1,  1, 1, -1,  1,  1,  1, -1, -1, -1, -1,  1,  1,  1,  1,  1, -1, -1,  1, -1, -1, -1, -1,  1, -1, -1, -1,  1,  1, -1,  1,  1, -1, -1,  1, -1, 1, -1, -1,  1, -1,  1, -1, -1,  1]</value>
     </param>
   </block>
   <block>
diff --git a/grc/hamnet70_mod_sc16qam.grc b/grc/hamnet70_mod_sc16qam.grc
index 590299d..1461e1c 100644
--- a/grc/hamnet70_mod_sc16qam.grc
+++ b/grc/hamnet70_mod_sc16qam.grc
@@ -340,7 +340,7 @@
     </param>
     <param>
       <key>value</key>
-      <value>[1, -1, -1, 1, -1, -1, -1, -1, -1, 1, 1, 1, -1, -1, -1, -1, 1, 1, -1, 1, -1, -1, -1, 1, -1, 1, 1, 1, -1, 1, 1, -1, -1, -1, 1, 1, -1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, 1, -1, 1, -1, 1, 1, -1, 1, -1, 1, -1, -1, -1, -1, -1, 1, -1, 1, -1, 1, -1, -1, -1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, 1, -1, 1, 1, -1, 1, 1, -1, -1, -1, 1, -1, -1, -1, 1, 1, -1, 1, 1, -1, -1, -1, -1, 1, 1, -1, -1, 1, -1, 1, 1, -1, 1, 1, -1, 1, -1, -1, -1, -1, 1, 1, -1, -1, 1, 1, 1, 1]</value>
+      <value>[-1, -1, -1,  1,  1,  1,  1, -1,  1,  1,  1, -1,  1, -1,  1,  1, -1, 1, -1, -1,  1, -1, -1, -1, -1, -1, -1,  1, -1,  1, -1,  1, -1,  1, 1, -1,  1, -1, -1, -1,  1,  1,  1, -1, -1,  1,  1, -1, -1,  1, -1, 1,  1,  1, -1,  1,  1, -1,  1,  1, -1, -1, -1, -1,  1, -1, -1,  1, 1, -1,  1, -1, -1,  1,  1,  1,  1,  1,  1, -1,  1, -1,  1, -1,  1, 1, -1,  1,  1,  1, -1, -1, -1, -1,  1,  1,  1,  1,  1, -1, -1,  1, -1, -1, -1, -1,  1, -1, -1, -1,  1,  1, -1,  1,  1, -1, -1,  1, -1, 1, -1, -1,  1, -1,  1, -1, -1,  1]</value>
     </param>
   </block>
   <block>
@@ -1116,6 +1116,53 @@
       <value>0xFF</value>
     </param>
   </block>
+  <block>
+    <key>hamnet70_insert_pilot_symbols</key>
+    <param>
+      <key>alias</key>
+      <value></value>
+    </param>
+    <param>
+      <key>comment</key>
+      <value></value>
+    </param>
+    <param>
+      <key>affinity</key>
+      <value></value>
+    </param>
+    <param>
+      <key>_enabled</key>
+      <value>2</value>
+    </param>
+    <param>
+      <key>_coordinate</key>
+      <value>(1980, 443)</value>
+    </param>
+    <param>
+      <key>_rotation</key>
+      <value>0</value>
+    </param>
+    <param>
+      <key>id</key>
+      <value>hamnet70_insert_pilot_symbols_0</value>
+    </param>
+    <param>
+      <key>offsets</key>
+      <value>[len(preamble)+128, len(preamble)+256]</value>
+    </param>
+    <param>
+      <key>maxoutbuf</key>
+      <value>0</value>
+    </param>
+    <param>
+      <key>minoutbuf</key>
+      <value>0</value>
+    </param>
+    <param>
+      <key>pilot_sequence</key>
+      <value>[1+1j, -1-1j, 1-1j, -1+1j]</value>
+    </param>
+  </block>
   <block>
     <key>import</key>
     <param>
@@ -1347,7 +1394,7 @@
     </param>
     <param>
       <key>_coordinate</key>
-      <value>(1972, 451)</value>
+      <value>(2188, 451)</value>
     </param>
     <param>
       <key>_rotation</key>
@@ -1415,7 +1462,7 @@
   </connection>
   <connection>
     <source_block_id>blocks_tagged_stream_mux_0</source_block_id>
-    <sink_block_id>virtual_sink_0</sink_block_id>
+    <sink_block_id>hamnet70_insert_pilot_symbols_0</sink_block_id>
     <source_key>0</source_key>
     <sink_key>0</sink_key>
   </connection>
@@ -1473,6 +1520,12 @@
     <source_key>pdu_out</source_key>
     <sink_key>in</sink_key>
   </connection>
+  <connection>
+    <source_block_id>hamnet70_insert_pilot_symbols_0</source_block_id>
+    <sink_block_id>virtual_sink_0</sink_block_id>
+    <source_key>0</source_key>
+    <sink_key>0</sink_key>
+  </connection>
   <connection>
     <source_block_id>interp_fir_filter_xxx_0</source_block_id>
     <sink_block_id>pad_sink_0</sink_block_id>
diff --git a/utils/filter_preamble.py b/utils/filter_preamble.py
index 7c2bfcf..e8f9ce1 100755
--- a/utils/filter_preamble.py
+++ b/utils/filter_preamble.py
@@ -4,13 +4,7 @@ import numpy as np
 import matplotlib.pyplot as pp
 import rrc
 
-pre = [1, -1, -1, 1, -1, -1, -1, -1, -1, 1, 1, 1, -1, -1, -1, -1, 1, 1, -1, 1,
-        -1, -1, -1, 1, -1, 1, 1, 1, -1, 1, 1, -1, -1, -1, 1, 1, -1, 1, 1, 1, 1,
-        1, 1, 1, 1, -1, -1, 1, -1, 1, -1, 1, 1, -1, 1, -1, 1, -1, -1, -1, -1,
-        -1, 1, -1, 1, -1, 1, -1, -1, -1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, 1,
-        -1, 1, 1, -1, 1, 1, -1, -1, -1, 1, -1, -1, -1, 1, 1, -1, 1, 1, -1, -1,
-        -1, -1, 1, 1, -1, -1, 1, -1, 1, 1, -1, 1, 1, -1, 1, -1, -1, -1, -1, 1,
-        1, -1, -1, 1, 1, 1, 1]
+pre = [-1, -1, -1,  1,  1,  1,  1, -1,  1,  1,  1, -1,  1, -1,  1,  1, -1, 1, -1, -1,  1, -1, -1, -1, -1, -1, -1,  1, -1,  1, -1,  1, -1,  1, 1, -1,  1, -1, -1, -1,  1,  1,  1, -1, -1,  1,  1, -1, -1,  1, -1, 1,  1,  1, -1,  1,  1, -1,  1,  1, -1, -1, -1, -1,  1, -1, -1,  1, 1, -1,  1, -1, -1,  1,  1,  1,  1,  1,  1, -1,  1, -1,  1, -1,  1, 1, -1,  1,  1,  1, -1, -1, -1, -1,  1,  1,  1,  1,  1, -1, -1,  1, -1, -1, -1, -1,  1, -1, -1, -1,  1,  1, -1,  1,  1, -1, -1,  1, -1, 1, -1, -1,  1, -1,  1, -1, -1,  1]
 
 pre_up = np.zeros(2 * len(pre) + 1)