title: RTL-SDR in GNU Radio 3.9
body: <p>I'm trying to make the RTL-SDR receive WBFM through GNU Radio (with Ubuntu 20.04), with this flowgraph:</p>
  <p><a href="https://i.stack.imgur.com/unsfR.png" rel="nofollow noreferrer">GNU Radio flowgraph</a></p>
  <p>But when I execute, it gives me this error message:</p>
  <pre><code>gr-osmosdr 0.2.0.0 (0.2.0) gnuradio 3.8.1.0
  built-in source types: file osmosdr fcd rtl rtl_tcp uhd miri hackrf bladerf rfspace airspy airspyhf soapy redpitaya freesrp 
  Using device #0 Realtek RTL2838UHIDIR SN: 00000001
  Found Rafael Micro R820T tuner
  [R82XX] PLL not locked!
  Exact sample rate is: 2000000,052982 Hz
  [R82XX] PLL not locked!
  Traceback (most recent call last):
    File &quot;rtl_sdr_receive.py&quot;, line 270, in &lt;module&gt;
      main()
    File &quot;rtl_sdr_receive.py&quot;, line 246, in main
      tb = top_block_cls()
    File &quot;rtl_sdr_receive.py&quot;, line 187, in __init__
      self.connect((self.rtlsdr_source_0, 0), (self.rational_resampler_xxx_0, 0))
    File &quot;/usr/lib/python3/dist-packages/gnuradio/gr/hier_block2.py&quot;, line 37, in wrapped
      func(self, src, src_port, dst, dst_port)
    File &quot;/usr/lib/python3/dist-packages/gnuradio/gr/hier_block2.py&quot;, line 100, in connect
      self.primitive_connect(*args)
  TypeError: primitive_connect(): incompatible function arguments. The following argument types are supported:
      1. (self: gnuradio.gr.gr_python.hier_block2_pb, block: gnuradio.gr.gr_python.basic_block) -&gt; None
      2. (self: gnuradio.gr.gr_python.hier_block2_pb, src: gnuradio.gr.gr_python.basic_block, src_port: int, dst: gnuradio.gr.gr_python.basic_block, dst_port: int) -&gt; None
  
  Invoked with: &lt;gnuradio.gr.gr_python.top_block_pb object at 0x7fae1b571af0&gt;, &lt;Swig Object of type 'gr::basic_block_sptr *' at 0x7fae1740c9c0&gt;, 0, &lt;gnuradio.gr.gr_python.hier_block2_pb object at 0x7fae19809770&gt;, 0
  swig/python detected a memory leak of type 'gr::basic_block_sptr *', no destructor found.
  </code></pre>
  <p>I'm using the GNU Radio 3.9 version because is the only one that works with rpitx (with TCP connection). But it seems to have trouble dealing with the RTL-SDR. Is this a software bug or I misconfigured something? Already tried to install GNU Radio 3.9 from PPA and from source, with same results in the end.</p>