# Works with GR 3.6, breaks with 3.7 **URL:** \ **Category:** GNU Radio\ **Created:** [October 13, 2014, 7:39pm UTC](https://www.ruby-forum.com/t/works-with-gr-3-6-breaks-with-3-7/232512 "2014-10-13T19:39:57Z")\ **Posts on this page:** 5\ **Page:** 2
**Author:** ![hagus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/9de053/32.png) [@hagus](https://www.ruby-forum.com/u/hagus)\ **Post date:** [November 4, 2014, 9:17pm UTC](https://www.ruby-forum.com/t/works-with-gr-3-6-breaks-with-3-7/232512/21 "2014-11-04T21:17:00Z")
Thanks Andy! Good catch - I made the changes you suggested. I was just doing a simple back of the envelope calculation to come up with channel size. It does look like cleans things up and adding the waterfall graphs does make it easier to see. Unfortunately, it does seem to change the decoding. I am still getting the same amount of CRC errors. Did the overall signal look right, like something that should be decodable? Anything else I should try? - Luke ---
**Author:** ![hagus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/9de053/32.png) [@hagus](https://www.ruby-forum.com/u/hagus)\ **Post date:** [November 5, 2014, 2:21am UTC](https://www.ruby-forum.com/t/works-with-gr-3-6-breaks-with-3-7/232512/22 "2014-11-05T02:21:15Z")
On Mon, 2014-11-03 at 22:13 -0500, Luke B. wrote: > Thanks Andy! Good catch - I made the changes you suggested. I was just > doing a simple back of the envelope calculation to come up with > channel size. It does look like cleans things up and adding the > waterfall graphs does make it easier to see. Unfortunately, it does > seem to change the decoding. I am still getting the same amount of CRC > errors. > > Did the overall signal look right, like something that should be decodable? So I put the output of the FLL into a quad demod block and compared its output to the PLL Freq det output. They are pretty much in line, except the quadrature demod block output shows occasional burst of noise for a few symbol times where the transmission must have stopped and restarted. The PLL freq detect block just makes something up during these times. So that seems generally OK. > Anything else I should try? Your PLL freq detector block output is swinging between -2 and 2. You might want to reduce the max and min freq by a factor of 2, so that the clock recovery block sees inputs limited to +/- 1.0. See Nick’s recommendation here: > **[Re: \[Discuss-gnuradio\] Works with GR 3.6, breaks with 3.7](https://lists.gnu.org/archive/html/discuss-gnuradio/2014-10/msg00473.html)** So after i did that, what I really noticed is that the correlator is just not marking preambles properly. See the top plot of the attached to window shots: Preamble\_marked\_late\_twice.png and Preamble\_marked\_early.png If the deinterleaver and/or crc block isn’t searching around for where the preamble really is, well that would explain it. Regards, Andy ---
**Author:** ![hagus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/9de053/32.png) [@hagus](https://www.ruby-forum.com/u/hagus)\ **Post date:** [November 5, 2014, 2:48am UTC](https://www.ruby-forum.com/t/works-with-gr-3-6-breaks-with-3-7/232512/23 "2014-11-05T02:48:41Z")
This is awesome! I just pulled master and I am recompiling it right now. Thanks you both so much for the help. I clearly still have some tuning work to do either way, but it would be great to get move up to 3.7. I will let you know if this clears it up. I have my fingers crossed that it will. ---
**Author:** ![hagus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/9de053/32.png) [@hagus](https://www.ruby-forum.com/u/hagus)\ **Post date:** [November 5, 2014, 4:57am UTC](https://www.ruby-forum.com/t/works-with-gr-3-6-breaks-with-3-7/232512/24 "2014-11-05T04:57:04Z")
That fixed it!! Nick & Andy - thank you both so much for looking into it. Without your help, there is no way I would have fixed this… and without Nick’s code I couldn’t have built it in the first place. - Luke ---
**Author:** ![hagus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/9de053/32.png) [@hagus](https://www.ruby-forum.com/u/hagus)\ **Post date:** [November 5, 2014, 2:29am UTC](https://www.ruby-forum.com/t/works-with-gr-3-6-breaks-with-3-7/232512/25 "2014-11-05T02:29:37Z")
Red face over here. There was a bug in correlate\_access\_code\_tag – which only gr-smartnet and gr-ais use, so far as I know. The fix was pulled into master a couple of days ago. This could explain the discrepancy you’re seeing in the preamble mark. Pull latest GR master, build, and see if it fixes what you’re seeing. –n On Tue, Nov 4, 2014 at 5:19 PM, Andy W. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) [Previous page](https://www.ruby-forum.com/t/works-with-gr-3-6-breaks-with-3-7/232512.md?page=1)