# Burst transmission USRP N210 + WBX **URL:** \ **Category:** GNU Radio\ **Created:** [June 1, 2015, 5:06pm UTC](https://www.ruby-forum.com/t/burst-transmission-usrp-n210-wbx/242160 "2015-06-01T17:06:50Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![Detlef\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/58f4c7/32.png) [@Detlef\_R](https://www.ruby-forum.com/u/Detlef_R)\ **Post date:** [June 1, 2015, 5:06pm UTC](https://www.ruby-forum.com/t/burst-transmission-usrp-n210-wbx/242160/1 "2015-06-01T17:06:50Z")
Hi everyone, I am writing here because I need some help with GNUradio and the UHD driver. My problem is: I want to send burst packet to USRP sink block. If I use the first flow-graph (see picture #1), all work fine. The “packet\_len” tag added by the “PDU to tagged stream” block is well understood by the UHD driver (No output characters like “U” or “D”…). But, I want to use a pulse shape filter before sending my signal over the air. (see picture #2). I used an “Interpolating FIR filter” block. I designed a RRC filter with firdes : firdes.root\_raised\_cosine(sps,sps, 1, eb,sps\*ntaps) with : sps = 4 eb = 0.35 ntaps = 44 When I run the second flow-graph with pulse shape filter (see picture #2), I get characters “tG” on the console window. 1 - I know this is because of the filter, and more particularly, the filter delay. I found that the filter delay for a RRC filter of NTAPS long, is : Delay = NTAPS/2. - First of all, Am I right with this assumption? 2 - I set the field “Sample delay” of the “Interpolating FIR Filter” to NTAPS/2, and added zeros at the end of my signal to flush the FIR filter. I can see that the tag is then delayed, and the last samples inside the filter are flushed. But, I always get the “tG” characters on the console window. 3 - I also used the two tags “tx\_sob” and “tx\_eob”. When I do not use pulse shape filter, all work well. But, when I want to use it, I got the same issue. I really don’t know where is my mistake so if someone could help me, it would be amazing. Thank in advance. Marius