# USRP in TDD mode **URL:** \ **Category:** GNU Radio\ **Created:** [September 23, 2009, 4:02am UTC](https://www.ruby-forum.com/t/usrp-in-tdd-mode/175953 "2009-09-23T04:02:32Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [September 23, 2009, 4:02am UTC](https://www.ruby-forum.com/t/usrp-in-tdd-mode/175953/1 "2009-09-23T04:02:32Z")
Hello. I’m trying to build a two-way TDD system with two USRP1 boxes in pure C++ using libusrp and inband\_2rxhb\_2tx.rbf firmware. Now I have working system where one USRP1 box transmits data and other box receives. I try to make the second box transmit data after it received certain frames. The issue is that when I try to enable transmitter on the second box the receive signal level significantly decreases. Typically received samples are in range [-15000; 15000], after enabling transmitter they are in range [-1000; 1000]. Does anyone have a clue of what I’m doing wrong? Thanks. The code I’m using: ``` std::string rbf_fname = "inband_2rxhb_2tx.rbf"; m_uTx = usrp_standard_tx::make(m_usrpNumber, (unsigned int)m_interpolationRate, 1, -1, 4096, 4096, rbf_fname); if (!m_uTx.get()) throw std::runtime_error("Couldn't create TX"); usrp_subdev_spec tx_spec(0, 0); unsigned int tx_mux = m_uTx->determine_tx_mux_value(tx_spec); m_uTx->set_mux(tx_mux); db_base_sptr tx_subdev = m_uTx->selected_subdev(tx_spec); m_txGain = tx_subdev->gain_max(); tx_subdev->set_gain(m_txGain); if (!m_uTx->tune(tx_subdev->which(), tx_subdev, g_tuneFrequency, ``` &m\_txTuneResult)) throw std::runtime\_error(“TX tune failed\n”); ``` tx_subdev->set_enable(true); // Enable RX m_uRx = usrp_standard_rx::make(m_usrpNumber, (unsigned int)m_decimationRate, 1, -1, usrp_standard_rx::FPGA_MODE_NORMAL, 4096, 4096, rbf_fname); if (!m_uRx.get()) throw std::runtime_error("Couldn't create RX"); // Select dautherboard usrp_subdev_spec rx_spec(0, 0); unsigned int rx_mux = m_uRx->determine_rx_mux_value(rx_spec); m_uRx->set_mux(rx_mux); m_rxGain = 60.0; db_base_sptr rx_subdev = m_uRx->selected_subdev(rx_spec); rx_subdev->set_gain(m_rxGain); if(!m_uRx->tune(rx_subdev->which(), rx_subdev, g_tuneFrequency, ``` &m\_rxTuneResult)) throw std::runtime\_error(“RX tune failed\n”); ``` rx_subdev->set_enable(true); ``` ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [September 23, 2009, 4:08am UTC](https://www.ruby-forum.com/t/usrp-in-tdd-mode/175953/2 "2009-09-23T04:08:59Z")
On Tuesday 22 September 2009 19:47:10 Andrey A wrote: > Hello. > I’m trying to build a two-way TDD system with two USRP1 boxes in pure C++ > using libusrp and inband\_2rxhb\_2tx.rbf firmware. IIRC the ib firmware has a bug not switching the antennaes correctly. Workaround: set RX antennae to RX2 and connect an antenna to each port. Stefan – Stefan Brüns / Bergstraße 21 / 52062 Aachen phone: +49 241 53809034 mobile: +49 151 50412019 ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [September 23, 2009, 6:34pm UTC](https://www.ruby-forum.com/t/usrp-in-tdd-mode/175953/3 "2009-09-23T18:34:22Z")
Hello. I tried connecting antenna to RX2 and signal strength increased. I use std\_2rxhb\_2tx.rbf with RFX2400 DB. Am I correct assuming that if only RX is enabled then RX/TX antenna is used and if with TX and RX are both enabled TX samples go to TX/RX antenna, and RX samples go thru RX2 ? If previous assumption is right, how to make TX and RX samples to thru the same antenna? Thanks. ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [September 23, 2009, 4:57pm UTC](https://www.ruby-forum.com/t/usrp-in-tdd-mode/175953/4 "2009-09-23T16:57:44Z")
Stefan, Thanks for reply. I tried std\_2rxhb\_2tx.rbf firmware from gnuradio 3.2.2 and results are the same. Without enabling transmitter at the receiver the received signal range is [-15e3; +15e3], and after enabling transmitter it became [-2400; +2400]. The workaround you mentioned is not applicable in my situation, since I need to receive and transmit from the same antenna. I’m not sure if I enable receiver and transmitter simultaneously in the right way. Thanks. On Tue, Sep 22, 2009 at 9:55 PM, Stefan Brüns ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [September 25, 2009, 1:30pm UTC](https://www.ruby-forum.com/t/usrp-in-tdd-mode/175953/5 "2009-09-25T13:30:54Z")
Hi. I finally figured it out. To automatically switch between TX and RX paths it’s needed to call subdev-\>select\_rx\_antenna(“TX/RX”); subdev-\>set\_auto\_tr(true); ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [November 21, 2014, 9:25am UTC](https://www.ruby-forum.com/t/usrp-in-tdd-mode/175953/6 "2014-11-21T09:25:10Z")
Hello Andrea, It would be great if you can share a little more information. Which code you have used and how you resolved the issue. Thanks