# Recommended gr-ais repo/branch/commit for GnuRadio 3.7.x (latest git) and UHD 3.7.1?

**URL:** <https://www.ruby-forum.com/t/recommended-gr-ais-repo-branch-commit-for-gnuradio-3-7-x-latest-git-and-uhd-3-7-1/240692>\
**Category:** GNU Radio\
**Created:** [April 25, 2014, 11:16pm UTC](https://www.ruby-forum.com/t/recommended-gr-ais-repo-branch-commit-for-gnuradio-3-7-x-latest-git-and-uhd-3-7-1/240692 "2014-04-25T23:16:01Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\
**Post date:** [April 25, 2014, 11:16pm UTC](https://www.ruby-forum.com/t/recommended-gr-ais-repo-branch-commit-for-gnuradio-3-7-x-latest-git-and-uhd-3-7-1/240692/1 "2014-04-25T23:16:01Z")

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Hi.

What is the recommended gr-ais repo/branch/commit that yields a working  
gr-ais with GnuRadio 3.7.x (git commit  
3831dd37c8df19e25fa258db4d393ee068889dae)  
and the Ettus UHD 3.7.1

GitHub shows this fork network:

> **[Network Graph · bistromath/gr-ais](https://github.com/bistromath/gr-ais/network)**
>
> Automatic Information System decoder for shipborne position reporting for the Gnuradio project - Network Graph · bistromath/gr-ais

Right now I’m using bistromath/gr-ais commit  
754c13ca4f1c3fb0d079d3a42002b0dade2268ff  
(master HEAD, IIRC), but I’m not getting _any_ !AIVDM output to the  
terminal window.

Regards,  
Andy

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**Author:** ![andywatts](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/d78d45/32.png) [@andywatts](https://www.ruby-forum.com/u/andywatts)\
**Post date:** [April 25, 2014, 11:18pm UTC](https://www.ruby-forum.com/t/recommended-gr-ais-repo-branch-commit-for-gnuradio-3-7-x-latest-git-and-uhd-3-7-1/240692/2 "2014-04-25T23:18:22Z")

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754C is correct. What hardware are you using? Are you sure you have a  
line-of-sight view to ships?

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**Author:** ![andywatts](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/d78d45/32.png) [@andywatts](https://www.ruby-forum.com/u/andywatts)\
**Post date:** [April 25, 2014, 11:24pm UTC](https://www.ruby-forum.com/t/recommended-gr-ais-repo-branch-commit-for-gnuradio-3-7-x-latest-git-and-uhd-3-7-1/240692/3 "2014-04-25T23:24:16Z")

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Ettus X310.

No ship needed; I have a known good transponder connected through RF  
cables and attenuators to the X310. 🙂

I can send AIS text and safety messages on demand, and the transponder  
will out its own position messages every 3 minutes since it is  
stationary.

Regards,  
Andy

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**Author:** ![andywatts](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/d78d45/32.png) [@andywatts](https://www.ruby-forum.com/u/andywatts)\
**Post date:** [May 13, 2014, 5:42pm UTC](https://www.ruby-forum.com/t/recommended-gr-ais-repo-branch-commit-for-gnuradio-3-7-x-latest-git-and-uhd-3-7-1/240692/4 "2014-05-13T17:42:21Z")

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On Fri, 2014-04-25 at 17:22 -0400, Andy W. wrote:  
[snip]

> > ```
> > GitHub shows this fork network:
> > https://github.com/bistromath/gr-ais/network
> > 
> > Right now I'm using bistromath/gr-ais commit
> > 754c13ca4f1c3fb0d079d3a42002b0dade2268ff
> > (master HEAD, IIRC), but I'm not getting *any* !AIVDM output
> > to the terminal window.
> > 
> > ```

Well, I’ve identified one problem.

The “unstuff” operation is being applied before the correlator for the  
start flag of 01111110 (0x7e). The start flag, end flag, and preamble  
are not subject to bit stuffing per ITU-R M.1371-4 Annex 2 Sections  
3.2.2.1 through 3.2.2.4.

I suspect this causes a problem with proper detection of the start of  
the message, as the unstuff, as I understand it, will change the start  
flag from 01111110 to 0111110m, where m is the first bit of the message  
payload.

Putting the unstuff operation after the correlators doesn’t fix  
everything though. All potential message decodes still fail the CRC  
check.

Bypassing the CRC check and inspecting the output !AIVDMs with gpsdecode  
verifies they are junk. ☹

Regards,  
Andy

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**Author:** ![andywatts](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/d78d45/32.png) [@andywatts](https://www.ruby-forum.com/u/andywatts)\
**Post date:** [May 13, 2014, 5:44pm UTC](https://www.ruby-forum.com/t/recommended-gr-ais-repo-branch-commit-for-gnuradio-3-7-x-latest-git-and-uhd-3-7-1/240692/5 "2014-05-13T17:44:12Z")

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Thanks for the report. Going to move this one offlist – have some stuff  
for you to try.

–n