diff --git a/grc/gsm_block_tree.xml b/grc/gsm_block_tree.xml
index 89319c8..219702a 100644
--- a/grc/gsm_block_tree.xml
+++ b/grc/gsm_block_tree.xml
@@ -27,6 +27,7 @@
       <block>gsm_txtime_setter</block>
       <block>gsm_gmsk_mod</block>
       <block>gsm_preprocess_tx_burst</block>
+      <block>gsm_gen_test_ab</block>
     </cat>
     <cat>
       <name>Logical channels demapping</name>
diff --git a/grc/transmitter/CMakeLists.txt b/grc/transmitter/CMakeLists.txt
index 76d079e..4df2abb 100644
--- a/grc/transmitter/CMakeLists.txt
+++ b/grc/transmitter/CMakeLists.txt
@@ -19,7 +19,9 @@
 
 install(FILES
     gsm_gmsk_mod.xml
-    gsm_txtime_bursts_tagger.xml 
-    gsm_txtime_setter.xml 
-    gsm_preprocess_tx_burst.xml DESTINATION share/gnuradio/grc/blocks
+    gsm_txtime_bursts_tagger.xml
+    gsm_txtime_setter.xml
+    gsm_preprocess_tx_burst.xml
+    gsm_gen_test_ab.xml
+    DESTINATION share/gnuradio/grc/blocks
 )
diff --git a/grc/transmitter/gsm_gen_test_ab.xml b/grc/transmitter/gsm_gen_test_ab.xml
new file mode 100644
index 0000000..3cb8b11
--- /dev/null
+++ b/grc/transmitter/gsm_gen_test_ab.xml
@@ -0,0 +1,19 @@
+<?xml version="1.0"?>
+<block>
+  <name>Gen Test AB</name>
+  <key>gsm_gen_test_ab</key>
+  <import>import grgsm</import>
+  <make>grgsm.gen_test_ab()</make>
+
+  <sink>
+    <name>bursts_in</name>
+    <type>message</type>
+    <optional>1</optional>
+  </sink>
+
+  <source>
+    <name>bursts_out</name>
+    <type>message</type>
+    <optional>1</optional>
+  </source>
+</block>
diff --git a/include/grgsm/transmitter/CMakeLists.txt b/include/grgsm/transmitter/CMakeLists.txt
index 29ccc4b..fab6f7c 100644
--- a/include/grgsm/transmitter/CMakeLists.txt
+++ b/include/grgsm/transmitter/CMakeLists.txt
@@ -23,5 +23,6 @@
 install(FILES
     txtime_setter.h 
     preprocess_tx_burst.h
+    gen_test_ab.h
     DESTINATION include/grgsm/transmitter
 )
diff --git a/include/grgsm/transmitter/gen_test_ab.h b/include/grgsm/transmitter/gen_test_ab.h
new file mode 100644
index 0000000..d2756f1
--- /dev/null
+++ b/include/grgsm/transmitter/gen_test_ab.h
@@ -0,0 +1,60 @@
+/* -*- c++ -*- */
+/* @file
+ * @author Piotr Krysik <ptrkrysik@gmail.com>
+ * @section LICENSE
+ * 
+ * Gr-gsm is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3, or (at your option)
+ * any later version.
+ * 
+ * Gr-gsm is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with gr-gsm; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ * 
+ */
+
+
+#ifndef INCLUDED_GSM_GEN_TEST_AB_H
+#define INCLUDED_GSM_GEN_TEST_AB_H
+
+#include <grgsm/api.h>
+#include <gnuradio/block.h>
+
+namespace gr {
+  namespace gsm {
+
+    /*!
+     * \brief A block that does preprocessing tasks before sending bursts to modulator.
+     * \ingroup gsm
+     *
+     * Currently it removes GSMTAP header from a burst and puts it in first part of PDU
+     * pair and removes tailing zeros from Access Bursts coming from TRX interface.
+     */
+    class GRGSM_API gen_test_ab : virtual public gr::block
+    {
+     public:
+      typedef boost::shared_ptr<gen_test_ab> sptr;
+
+      /*!
+       * \brief Return a shared_ptr to a new instance of gsm::gen_test_ab.
+       *
+       * To avoid accidental use of raw pointers, gsm::gen_test_ab's
+       * constructor is in a private implementation
+       * class. gsm::gen_test_ab::make is the public interface for
+       * creating new instances.
+       */
+      static sptr make();
+    };
+
+  } // namespace gsm
+} // namespace gr
+
+#endif /* INCLUDED_GSM_GEN_TEST_AB_H */
+
diff --git a/lib/transmitter/CMakeLists.txt b/lib/transmitter/CMakeLists.txt
index c61654a..eb53162 100644
--- a/lib/transmitter/CMakeLists.txt
+++ b/lib/transmitter/CMakeLists.txt
@@ -20,4 +20,5 @@
 add_sources(
    txtime_setter_impl.cc
    preprocess_tx_burst_impl.cc
+   gen_test_ab_impl
 )
diff --git a/lib/transmitter/gen_test_ab_impl.cc b/lib/transmitter/gen_test_ab_impl.cc
new file mode 100644
index 0000000..66873db
--- /dev/null
+++ b/lib/transmitter/gen_test_ab_impl.cc
@@ -0,0 +1,107 @@
+/* -*- c++ -*- */
+/* @file
+ * @author Piotr Krysik <ptrkrysik@gmail.com>
+ * @section LICENSE
+ * 
+ * Gr-gsm is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3, or (at your option)
+ * any later version.
+ * 
+ * Gr-gsm is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with gr-gsm; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ * 
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <gnuradio/io_signature.h>
+#include <grgsm/gsmtap.h>
+#include <grgsm/gsm_constants.h>
+#include "gen_test_ab_impl.h"
+
+namespace gr {
+  namespace gsm {
+
+    static uint8_t rach_synch_seq[] = {
+      0, 1, 0, 0, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1,
+      1, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0  ,
+      1, 0, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0,
+    };
+  
+//    static uint8_t AB[] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 0, 1, 0, 1, 0, 0, 1, 0, 0, 1, 1, 0, 1, 0, 1, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
+//    static uint8_t AB[] = {0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1};
+// static uint8_t AB[] = { 1, 1, 0, 0, 0, 1, 0, 1, 1, 0, 1, 1, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 0, 1, 0, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 1, 1, 0, 0, 1, 1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 1, 0, 0, 1, 1, 1, 0, 1, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1};
+  static uint8_t AB[] = {1,1,1,1,1,1,1,1,1,0,1,1,0,1,0,0,1,0,0,0,0,0,0,0,0,1,1,0,0,1,1,0,0,1,0,1,0,1,0,1,1,1,0,0,0,0,1,1,1,0,0,1,0,0,0,1,0,1,0,1,0,0,1,0,1,0,1,1,0,1,1,0,0,1,0,1,0,0,0,1,1,0,0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1
+  ,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1};
+    gen_test_ab::sptr
+    gen_test_ab::make()
+    {
+      return gnuradio::get_initial_sptr
+        (new gen_test_ab_impl());
+    }
+
+    /*
+     * The private constructor
+     */
+    gen_test_ab_impl::gen_test_ab_impl()
+      : gr::block("gen_test_ab",
+              gr::io_signature::make(0, 0, 0),
+              gr::io_signature::make(0, 0, 0))
+    {
+        message_port_register_in(pmt::intern("bursts_in"));
+        message_port_register_out(pmt::intern("bursts_out"));
+
+        set_msg_handler(pmt::intern("bursts_in"),  boost::bind(&gen_test_ab_impl::generate_ab,   this, _1));
+    }
+
+    /*
+     * Our virtual destructor.
+     */
+    gen_test_ab_impl::~gen_test_ab_impl()
+    {
+    }
+    
+    void gen_test_ab_impl::generate_ab(pmt::pmt_t burst)
+    {
+        uint8_t buf[sizeof(gsmtap_hdr) + 148];
+        struct gsmtap_hdr *tap_header = (struct gsmtap_hdr *) buf;
+        uint8_t *access_burst = buf + sizeof(gsmtap_hdr);
+
+//        memset(access_burst, 0, 8); /* TB */
+//        memcpy(access_burst + 8, rach_synch_seq, 41); /* sync seq */
+//        memcpy(access_burst + 49, AB, 36); /* payload */
+//        memset(access_burst + 85, 0, 63); /* TB + GP */
+        
+        memcpy(access_burst, AB, 148);
+        
+        gsmtap_hdr * header = (gsmtap_hdr *)(pmt::blob_data(pmt::cdr(burst)));
+        uint32_t frame_nr = be32toh(header->frame_number);
+        frame_nr = (frame_nr+51)% (26*51*2048);
+        
+        tap_header->version = GSMTAP_VERSION;
+        tap_header->hdr_len = sizeof(gsmtap_hdr) / 4;
+        tap_header->type = GSMTAP_TYPE_UM_BURST;
+        tap_header->sub_type = GSMTAP_BURST_ACCESS;
+        tap_header->frame_number = htobe32(frame_nr);
+        tap_header->timeslot = header->timeslot;
+        tap_header->arfcn = 0;
+        
+        pmt::pmt_t blob = pmt::make_blob(buf, sizeof(gsmtap_hdr) + BURST_SIZE);
+        pmt::pmt_t pdu_header = pmt::make_dict();
+        
+        pmt::pmt_t new_msg = pmt::cons(pdu_header, blob);
+        message_port_pub(pmt::intern("bursts_out"), new_msg);
+    }
+  } /* namespace gsm */
+} /* namespace gr */
+
diff --git a/lib/transmitter/gen_test_ab_impl.h b/lib/transmitter/gen_test_ab_impl.h
new file mode 100644
index 0000000..366481e
--- /dev/null
+++ b/lib/transmitter/gen_test_ab_impl.h
@@ -0,0 +1,47 @@
+/* -*- c++ -*- */
+/* @file
+ * @author Piotr Krysik <ptrkrysik@gmail.com>
+ * @section LICENSE
+ * 
+ * Gr-gsm is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3, or (at your option)
+ * any later version.
+ * 
+ * Gr-gsm is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with gr-gsm; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ * 
+ */
+
+#ifndef INCLUDED_GSM_GEN_TEST_AB_IMPL_H
+#define INCLUDED_GSM_GEN_TEST_AB_IMPL_H
+
+#include <grgsm/transmitter/gen_test_ab.h>
+#include <grgsm/misc_utils/time_spec.h>
+#include <grgsm/misc_utils/fn_time.h>
+
+namespace gr {
+  namespace gsm {
+
+    class gen_test_ab_impl : public gen_test_ab
+    {
+     private:
+      void generate_ab(pmt::pmt_t burst);
+      
+     public:
+      gen_test_ab_impl();
+      ~gen_test_ab_impl();
+    };
+
+  } // namespace gsm
+} // namespace gr
+
+#endif /* INCLUDED_GSM_GEN_TEST_AB_IMPL_H */
+
diff --git a/swig/grgsm_swig.i b/swig/grgsm_swig.i
index 65c48be..005033f 100644
--- a/swig/grgsm_swig.i
+++ b/swig/grgsm_swig.i
@@ -1,7 +1,7 @@
 /* -*- c++ -*- */
 /*
  * @file
- * @author (C) 2014 by Piotr Krysik <ptrkrysik@gmail.com>
+ * @author (C) 2014-2017 by Piotr Krysik <ptrkrysik@gmail.com>
  * @section LICENSE
  *
  * Gr-gsm is free software; you can redistribute it and/or modify
@@ -72,6 +72,7 @@
 #include "grgsm/misc_utils/fn_time.h"
 #include "grgsm/transmitter/txtime_setter.h"
 #include "grgsm/transmitter/preprocess_tx_burst.h"
+#include "grgsm/transmitter/gen_test_ab.h"
 #include "grgsm/misc_utils/trx_burst_if.h"
 %}
 
@@ -144,10 +145,6 @@
 GR_SWIG_BLOCK_MAGIC2(gsm, controlled_fractional_resampler_cc);
 %include "grgsm/misc_utils/extract_cmc.h"
 GR_SWIG_BLOCK_MAGIC2(gsm, extract_cmc);
-%include "grgsm/misc_utils/trx_burst_if.h"
-GR_SWIG_BLOCK_MAGIC2(gsm, trx_burst_if);
-
-
 %include "grgsm/qa_utils/burst_sink.h"
 GR_SWIG_BLOCK_MAGIC2(gsm, burst_sink);
 %include "grgsm/qa_utils/burst_source.h"
@@ -185,3 +182,9 @@
 GR_SWIG_BLOCK_MAGIC2(gsm, txtime_setter);
 %include "grgsm/transmitter/preprocess_tx_burst.h"
 GR_SWIG_BLOCK_MAGIC2(gsm, preprocess_tx_burst);
+
+%include "grgsm/transmitter/gen_test_ab.h"
+GR_SWIG_BLOCK_MAGIC2(gsm, gen_test_ab);
+
+%include "grgsm/misc_utils/trx_burst_if.h"
+GR_SWIG_BLOCK_MAGIC2(gsm, trx_burst_if);