On Tue, Jan 23, 2018 at 12:27:23PM -0500, Daryl Lee via USRP-users wrote: > I've been using an NI USRP-2953R for several months with a trivial > configuration: sending and receiving in "half-duplex" mode on the "RF 0" > receive and transmit antennas. Now I need to try using the RF 0 RX antenna > and the RF 1 TX antenna. I'm using this terminology because I'm a bit > uncertain about the other terminology (daugherboard, front-end, sub-device, > channel, port, ...). I found the application note "Frontends, Sub-Device > Specifications, and Antenna Port Selection", which is very helpful, but > having an example would be efven more helpful. The UHD library distribution > example "txrx_loopback_to_file" leads me to believe that I need a separate > multi_usrp object for each direction (tx_usrp, rx_usrp), but I also need to > work out the correct sub-device specification "X:Y" to pass in the arg > string. > > Can anyone point me to other documents/tutorials/examples of such a > configuration?
Daryl, you don't need several multi_usrp instantiations (and in fact, they would point to the same underlying device due to some device caching). There are multiple ways to achieve this: 1. Set RX subdev spec to "A:0", and TX subdev spec to "B:0". This will select the A-side for RX, and the B-side for TX. Then, create one streamer on channel 0 for each direction (call get_rx_stream() and get_tx_stream() with default args). 2. Set the RX and TX subdev spec both to "A:0 B:0" (this is the default). Then, call get_rx_stream() with channels = [0] and get_tx_stream() with channels = [1] (both are vectors of length one). Both will achieve the same effect. The difference is when calling other multi_usrp calls such as set_rx_freq() or set_tx_freq(). The channel indexing is relative to the subdev spec. -- Martin
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