title: GNURadio PSK bit recovery
body: <p>I have followed the wonderful GNURadio Guided Tutorial PSK Demodulation:
  <a href="https://wiki.gnuradio.org/index.php/Guided_Tutorial_PSK_Demodulation" rel="nofollow noreferrer">https://wiki.gnuradio.org/index.php/Guided_Tutorial_PSK_Demodulation</a></p>
  
  <p>I've created a very simple DBPSK modulator
  <a href="https://i.stack.imgur.com/zWu48.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/zWu48.png" alt="enter image description here"></a></p>
  
  <p>I feed in a series of bits that are sliding. So the first byte I feed in is 0x01, the next byte is 0x02, 0x04, 0x08 and so on. This is the output of hd:</p>
  
  <pre><code>00000000  00 00 ac 0e d0 f0 20 40  81 02 04 08 10 00 20 40  |...... @...... @|
  00000010  81 02 04 08 10 00 20 40  81 02 04 08 10 00 20 40  |...... @...... @|
  *
  00015000
  </code></pre>
  
  <p>The first few bytes are garbage, but then you can see the pattern. Looking at the second line you see:
  0x81, 0x02, 0x04, 0x08, 0x10, 0x00, 0x20, 0x40, 0x81</p>
  
  <p>The walking ones is there, but after 0x10, the PSK demodulator receives a 0x00, then a few bytes later is receives a 0x81. It almost seems like the timing recovery is off.  </p>
  
  <p>Has anyone else seen something like this?</p>