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Re: [Discuss-gnuradio] Re: Mode S and ADS-B

From: Martin Dvh
Subject: Re: [Discuss-gnuradio] Re: Mode S and ADS-B
Date: Sat, 14 Apr 2007 16:03:04 +0200
User-agent: Debian Thunderbird 1.0.2 (X11/20070113)

Eric A. Cottrell wrote:
> Hello,
> I am making good progress.
> The first couple of weeks or so (months?) I was collecting information.
>  I managed to get some design articles about Mode S transponders,
> various protocol specifications, and comments.  I was able to decode
> some packets by sight using the oscilloscope program.  The bit timing is
> very tight.  Thanks go to Matt Ettus for designing a board that can
> handle a 4 MSPS sampling rate.  It was now coding time!  I reviewed some
> GNURadio design guidelines and how to write a module.
> Of course the name is most important.  I decided on a subdirectory off
> gnuradio named gr-mode-s.  gr-transponder would make it look like
> sending as well as receiving.  My project is focused on Mode S data and
> derivatives (TCAS, ACAS, ADS-B, TIS-B, etc).  I am open to a better name
> as the mode-s name forced me to use the prefix of mode_s for things.
> I decided to use gr-pager as the model as it is the closest to what I
> want to do.  I eliminated some blocks but may put them back in.  I
> basically have a slicer, decoder/framer, and parser C++ blocks.  I use
> python code to put the blocks together into a mode S decoder superblock.
> I appreciate the autoconf/automake and the whole gnuradio build scheme.
>    For a programmer who has only done small gcc projects it looks like
> it is real work to do things from scratch.  I was able to figure out
> what most of the autoconf/automake files are for.  I replaced the pager
> prefixes with mode_s, add the required .m4 files, etc.  I was amazed
> that I got my new project integrated into the build tree quickly.  The
> major part of the time was spent getting my code to work.
> So I am jumping up and down with joy as I can now decode Mode S.  I can
> now work on improving the slicer, add decoding of the messages, etc.  It
> seems like I am not getting hundreds of miles of range due to the
> antenna setup but I get enough to work on the decoders.
> A future to-do is to submit my code.  I guess I need to join the patch list.
You can ask Eric to get you a svn account.
Then you can make your own private branche of gnuradio with your work in 
progress (usually called wip)
As soon as things stabilize in your branche it can be easaly integrated back 
into trunk.
But as long as you working on it, interested people can try out the latest 
version of your code.

See for example my svn subdirs:
I have a digital-wip branche which is work in progress for digital QAM stuff
general-wip which is my work in progress for general gnuradio things
(latest addition is gr-cxadc, a driver for cx2388x capture cards to use as a 
general purpose high-speed ADC frontend as a cheap alternative for
an USRP)


> It would be neat if I could get hardware that is smaller sized.  Maybe a
> USRP Jr board that allows one receiver or one receiver and one
> transmitter board,  I could also use one with a LFRX board and dedicate
> it to my AR5000.
> 73 Eric
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