# Usrp\_sink tags confusion **URL:** \ **Category:** GNU Radio\ **Created:** [August 12, 2015, 8:49am UTC](https://www.ruby-forum.com/t/usrp-sink-tags-confusion/242974 "2015-08-12T08:49:58Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![Rafa\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/958977/32.png) [@Rafa\_F](https://www.ruby-forum.com/u/Rafa_F)\ **Post date:** [August 12, 2015, 8:49am UTC](https://www.ruby-forum.com/t/usrp-sink-tags-confusion/242974/1 "2015-08-12T08:49:58Z")
Dear all, I would like to do some simple frequency hopping over my USRP (x300 with UBX-160 daugherboard). To that end I wish to use the following tags: - tx\_len (defined in the length-tag field of the USRP sink). This (naturally) gives the length of a burst -tx\_freq -\> used to change the centre frequency of the USRP before the first bit of every packet -tx\_time -\> used to have a fixed time interval between 2 consecutive bursts Here is my confusion: When I add the tx\_len tag to specific items, I get NO “tG”-output from gnuradio: this means that I am adding the tx\_len tag correctly at the first item of every burst according to the specified burst length, correct? However, when I add the tx\_freq tag to the same item that I add the tx\_len tag to, I get these messages from gnuradio: DEBUG: Received tx\_freq mid-burst. DEBUG: Received tx\_freq on start of burst. DEBUG: Received command: freq – Tune Request: 5793.000000 MHz – The RF LO does not support the requested frequency: – Requested LO Frequency: 5793.000000 MHz – RF LO Result: 5793.003663 MHz – Attempted to use the DSP to reach the requested frequency: – Desired DSP Frequency: -0.003663 MHz – DSP Result: -0.003663 MHz – Successfully tuned to 5793.000000 MHz How can the tx\_freq be received mid\_burst if I place it in the same item as the tx\_len tag, i.e. on the first item of a new burst? And how can it be received mid-burst AND on start of burst? Any help is greatly appreciated! Kind regards, Matija