# Re: modulation blocks propagate eob tag? **URL:** \ **Category:** GNU Radio\ **Created:** [February 25, 2013, 6:00pm UTC](https://www.ruby-forum.com/t/re-modulation-blocks-propagate-eob-tag/226911 "2013-02-25T18:00:14Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![breuerp](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/77aa72/32.png) [@breuerp](https://www.ruby-forum.com/u/breuerp)\ **Post date:** [February 25, 2013, 6:00pm UTC](https://www.ruby-forum.com/t/re-modulation-blocks-propagate-eob-tag/226911/1 "2013-02-25T18:00:14Z")
Hi, With gnuradio 3.6.3 I am using the gr\_message\_burst\_source to generate messages (one message per second) and set the bob and eob correctly. After this block I connect the following blocks to send bpsk modulated messages : packet\_to\_unpacket\_bb, map\_bb, chuncks\_to\_symbol, rrc\_filter and the uhd\_usrp\_sink. However, I get many “U” characters in the screen, and many errors in the reception. I think that one or many blocks of the previous ones do not propagate the tags properly. I appreciate any help to solve this problem/question. Thank you. Best regards, Pablo B… ---
**Author:** ![breuerp](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/77aa72/32.png) [@breuerp](https://www.ruby-forum.com/u/breuerp)\ **Post date:** [February 25, 2013, 6:10pm UTC](https://www.ruby-forum.com/t/re-modulation-blocks-propagate-eob-tag/226911/2 "2013-02-25T18:10:46Z")
Hi Pablo, you can use the tag\_debug or metadata file sink blocks to see if your tags are propagating correctly. MB On Mon, Feb 25, 2013 at 04:58:52PM +0000, Pablo B. wrote: > Hi, With gnuradio 3.6.3 I am using the gr\_message\_burst\_source to generate > messages (one message per second) and set the bob and eob correctly. After > this block I connect the following blocks to send bpsk modulated messages > : packet\_to\_unpacket\_bb, map\_bb, chuncks\_to\_symbol, rrc\_filter and the > uhd\_usrp\_sink. However, I get many “U” characters in the screen, and many > errors in the reception. I think that one or many blocks of the previous ones > do not propagate the tags properly. I appreciate any help to solve this problem > /question. Thank you. – Karlsruhe Institute of Technology (KIT) Communications Engineering Lab (CEL) Dipl.-Ing. Martin B. Research Associate Kaiserstraße 12 Building 05.01 76131 Karlsruhe Phone: +49 721 608-43790 Fax: +49 721 608-46071 www.cel.kit.edu KIT – University of the State of Baden-Württemberg and National Laboratory of the Helmholtz Association ---
**Author:** ![breuerp](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/77aa72/32.png) [@breuerp](https://www.ruby-forum.com/u/breuerp)\ **Post date:** [February 25, 2013, 9:33pm UTC](https://www.ruby-forum.com/t/re-modulation-blocks-propagate-eob-tag/226911/3 "2013-02-25T21:33:34Z")
On 02/25/2013 10:58 AM, Pablo B. wrote: > Hi, With gnuradio 3.6.3 I am using the gr\_message\_burst\_source to generate > messages (one message per second) and set the bob and eob correctly. After > this block I connect the following blocks to send bpsk modulated messages > : packet\_to\_unpacket\_bb, map\_bb, chuncks\_to\_symbol, rrc\_filter and the > uhd\_usrp\_sink. However, I get many “U” characters in the screen, and many > errors in the reception. I think that one or many blocks of the previous > ones do not propagate the tags properly. I appreciate any help to solve > this problem/question. Thank you. When the EOB goes through the modulator chain, there is some interpolation in the item count, and the tag ends up not on the very last item in the burst. In this project, there is a block to correct this issue, this its called packet gate or eob gate: [https://github.com/jmalsbury/pre-cog/wiki](https://github.com/jmalsbury/pre-cog/wiki) -josh