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<p><div class="WordSection1"><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;">Hi all,<o></o></span></p><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;"><o> </o></span></p><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;">Firstly, thank you to Max for the Slashdot mention!<o></o></span></p><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;"><o> </o></span></p><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;">I’d like to continue the ultra-cheap SDR theme with this video that demonstrates the RTL2832 USB DVB-T dongle successfully receiving an encrypted P25 signal, which is then decrypted and decoded by OP25 (represented by the new ‘OP25 Decoder’ GRC block in <a href="http://wiki.spench.net/wiki/gr-baz#rtl_source_c">gr-baz</a>), and sent to the soundcard:<o></o></span></p><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;"><o> </o></span></p><p class="MsoNormal"><a href="http://www.youtube.com/watch?v=wShOLgW2tmI">http://www.youtube.com/watch?v=wShOLgW2tmI</a><o></o></p><p class="MsoNormal"><o> </o></p><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;">The block lets you specify a key to enable DES-OFB decryption of an incoming stream. As Matt Robert suggested, this could be further developed by having a ‘key map file’, that contains the correct key for a specific AlgID/etc.<o></o></span></p><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;"><o> </o></span></p><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;">All the RTL2832 code is in gr-baz. The patch enabling decryption support is from a rather old version of the source (r219), so if anyone would like to make it current for submission into the repo, please let me know and I can send it out!<o></o></span></p><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;"><o> </o></span></p><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;">I also added another new block called ‘Message Callback’, which is used to trigger callbacks in the GRC generated code based on messages sent by other blocks to messages queues. If you watch the video or visit my wiki, you’ll see all the tuning/channel selection/filtering/audio is done by the appropriate blocks in GRC – separate from the OP25 code (this is different from it all being in the one Python file, e.g. audio_p25_rx). You may recall the FSK4 block outputs auto-tuning messages to the Frequency Translating FIR filter (channel selection block) <b>before</b> the FSK4 block. This feedback loop is handled internally in the existing stand-alone Python files, but needs to be replicated in GRC – hence the new block. The ‘Message Callback’ block connects to the ‘tuning’ output of the OP25 Decoder block, and is told about the ‘auto_tune_freq’ GRC variable to update when a message arrives with a new value. This GRC variable is subsequently used to update the Centre Frequency in the Frequency Translating FIR filter (channel selection block) to fulfil the FSK4 block’s request.<o></o></span></p><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;"><o> </o></span></p><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;">If you’re into GNU Radio, I just posted a much longer update with the latest RTL2832 developments (including a completely re-written ‘librtl2832++’) to the GNU Radio Discussion list.<o></o></span></p><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;"><o> </o></span></p><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;">Kind regards,<o></o></span></p><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;">Balint <a href="http://twitter.com/spenchdotnet">@spenchdotnet</a><o></o></span></p><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;"><o> </o></span></p><div style="border-left:solid blue 1.5pt;"><div><div style="border-top:solid #B5C4DF 1.0pt;"><p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;">From:</span></b><span lang="EN-US" style="font-size:10.0pt;"> op25-dev@yahoogroups.com [mailto:op25-dev@yahoogroups.com] <b>On Behalf Of </b>ikj1234i<br><b>Sent:</b> Sunday, 1 April 2012 10:20 PM<br><b>To:</b> op25-dev@yahoogroups.com<br><b>Subject:</b> [op25-dev] congrats to Balint: on Slashdot ! ! !<o></o></span></p></div></div><p class="MsoNormal"><o> </o></p><p class="MsoNormal"> <o></o></p><div id="ygrp-mlmsg"><div id="ygrp-msg"><div id="ygrp-text"><p><a href="http://hardware.slashdot.org/story/12/03/31/1914217/software-defined-radio-for-11">http://hardware.slashdot.org/story/12/03/31/1914217/software-defined-radio-for-11</a><o></o></p></div><div><p class="MsoNormal"><span style="color:white;"><o></o></span></p></div></div></div></div></div></p>
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