# Channel setting for USRP **URL:** \ **Category:** GNU Radio\ **Created:** [August 12, 2015, 1:34am UTC](https://www.ruby-forum.com/t/channel-setting-for-usrp/242972 "2015-08-12T01:34:32Z")\ **Posts on this page:** 3\ **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, 1:34am UTC](https://www.ruby-forum.com/t/channel-setting-for-usrp/242972/1 "2015-08-12T01:34:32Z")
Hi all, I want to transmit the data between two USRP’s and make them communicate with each other. But I guess the packets are not being received properly. My USRP daughterboard model is XCVR2450. When I am running ./benchmark\_tx.py -f 2.435G, it is starting to transmit the packets but a small error occured given below, linux; GNU C++ version 4.8.4; Boost\_105500; UHD\_003.009.git-144-g407e3086 Using Volk machine: avx\_64\_mmx – Opening a USRP1 device… – Using FPGA clock rate of 64.000000MHz… No gain specified. Setting gain to 7.500000 (from [-20.000000, 35.000000]) UHD Warning: The hardware does not support the requested TX sample rate: Target sample rate: 0.050000 MSps Actual sample rate: 0.250000 MSps Symbol Rate: 25000.000000 Requested sps: 2.000000 Given sample rate: 250000.000000 Actual sps for rate: 10.000000 Requested sample rate: 50000.000000 Actual sample rate: 250000.000000 …U…terminate called after throwing an instance of ‘uhd::runtime\_error’ what(): RuntimeError: usb tx2 transfer status: 1 Aborted (core dumped). But towards the receiver side, I gave the command ./benchmark\_rx.py -f 2.435GG,it has shown the result given below with n\_right=0. linux; GNU C++ version 4.8.4; Boost\_105500; UHD\_003.009.git-144-g407e3086 Using Volk machine: avx\_64\_mmx – Opening a USRP1 device… – Using FPGA clock rate of 64.000000MHz… No gain specified. Setting gain to 56.250000 (from [0.000000, 112.500000]) UHD Warning: The hardware does not support the requested RX sample rate: Target sample rate: 0.050000 MSps Actual sample rate: 0.250000 MSps Symbol Rate: 25000.000000 Requested sps: 2.000000 Given sample rate: 250000.000000 Actual sps for rate: 10.000000 Requested sample rate: 50000.000000 Actual sample rate: 250000.000000 ok = False pktno = 53034 n\_rcvd = 1 n\_right = 0 ok = False pktno = 24 n\_rcvd = 2 n\_right = 0 ok = False pktno = 35 n\_rcvd = 3 n\_right = 0 ok = False pktno = 44 n\_rcvd = 4 n\_right = 0 ok = False pktno = 46 n\_rcvd = 5 n\_right = 0 ok = False pktno = 46 n\_rcvd = 6 n\_right = 0 ok = False pktno = 3872 n\_rcvd = 7 n\_right = 0 ok = False pktno = 12304 n\_rcvd = 8 n\_right = 0 ok = False pktno = 49 n\_rcvd = 9 n\_right = 0 ok = False pktno = 50 n\_rcvd = 10 n\_right = 0 ok = False pktno = 54 n\_rcvd = 11 n\_right = 0 ok = False pktno = 200 n\_rcvd = 12 n\_right = 0 ok = False pktno = 63 n\_rcvd = 13 n\_right = 0 How would I be able to know if the USRP is maintained in the same channel?What commands do I need to give so that the packet is received correctly as n\_right=1. My USRP can access in the range of 2.4GHZ to 5GHZ. Please advice as to what I can do. Thanks Regards, John ---
**Author:** ![softf5ajivanet](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/9f8e36/32.png) [@softf5ajivanet](https://www.ruby-forum.com/u/softf5ajivanet)\ **Post date:** [August 22, 2015, 2:47pm UTC](https://www.ruby-forum.com/t/channel-setting-for-usrp/242972/2 "2015-08-22T14:47:27Z")
Hi John or Ravi, I don’t know whether your questions have been solved. I think Tom has extensively discussed [1] a lot of things that can happen here, so you’re aware of the fact that transmission-wise, there’s the whole world of radio channel that could distort your signal. So let’s talk a bit about what’s wrong with the hardware settings you use: _Transmitter_ > No gain specified. > You should really specify the gain. That defines how much power comes > out of your antenna. For a start, you might want to use a moderately > high setting, so something like 25 would be good. > Actual sample rate: 250000.000000 > I you must really fix that. As I’ve explained two weeks ago: > as the warning says, the sampling rates you’re trying to use on both > TX and RX side are lower than the minimum sampling rates. You should > fix that. It’s not hard, you just need basic understanding of what the > program does. > To spell this out: the data rate together with the samples per symbol > define your sample rate. For your USRP, this rate must be at least > 250kS/s. The effect of you not correcting your flow graph is that the > script generates a signal that the USRP converts to an analog signal at > five times the speed that you specify – this means all frequencies with > your complex baseband are five times as high! > …U… Oh, that’s bad. You’re seeing an U like “Underrun”, which means your PC was too slow at supplying samples to the USRP. This seriously breaks your signal. Now, I don’t know your computer, but I know that 250kS/s is really no load for any PC nowadays – I haven’t seen any PC being too slow for this very low rate. How old is your PC? Are you doing something else on it? Or are you running in a virtual machine? > terminate > called after throwing an instance of ‘uhd::runtime\_error’ > what(): RuntimeError: usb tx2 transfer status: 1 > Aborted (core dumped). > That’s even worse. It can happen if you cancel the script using > “ctrl+c”, but this looks like there is something seriously wrong with > your USB2 controller. Again, what computer are you using? _Receiver_ > No gain specified. > Setting gain to 56.250000 (from [0.000000, 112.500000]) > The same as above. More gain = more signal power, but don’t overdo it. > You will need to experiment. As Tom explained, letting the transmitter > run and observing the spectrum with something like usrp\_spectrum\_sense > will help you determine settings that make sense. First, however, I can > not stress this enough, fix your sample rate issue! > Requested sample rate: 50000.000000 > Actual sample rate: 250000.000000 > The same as above. Both your RX and your TX are running at 250kS/s > instead of the 50kS/s that you specified. Luckily, this means that the > effect kind of cancels itself out – still, fix that! - General\* > How would I be able to know if the USRP is maintained in the same > channel? > You set both TX and RX to the same frequency, and since there is only > one physical medium (the space between the RX and TX antenna), you can > be sure. There’s no concept like “this specific part of spectrum belongs > to channel number 12” in the physical world – just frequencies, and > Maxwell’s Equations governing the propagation of radio waves. > What commands do I need to give so that the packet is received > correctly as n\_right=1. > Tom has explained enough that it’s not like that. You will need to find > out yourself. Best regards, Marcus PS: Do you have a preferred name to address you by? “Ravi” is as fine to me as “John”, so I’d suggest you pick one and stick with that, because it’s less confusing. [1] “Communication Problems between 2 USRP” email thred ---
**Author:** ![softf5ajivanet](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/9f8e36/32.png) [@softf5ajivanet](https://www.ruby-forum.com/u/softf5ajivanet)\ **Post date:** [August 22, 2015, 2:47pm UTC](https://www.ruby-forum.com/t/channel-setting-for-usrp/242972/3 "2015-08-22T14:47:28Z")
Hi John or Ravi, I don’t know whether your questions have been solved. I think Tom has extensively discussed [1] a lot of things that can happen here, so you’re aware of the fact that transmission-wise, there’s the whole world of radio channel that could distort your signal. So let’s talk a bit about what’s wrong with the hardware settings you use: _Transmitter_ > No gain specified. > You should really specify the gain. That defines how much power comes > out of your antenna. For a start, you might want to use a moderately > high setting, so something like 25 would be good. > Actual sample rate: 250000.000000 > I you must really fix that. As I’ve explained two weeks ago: > as the warning says, the sampling rates you’re trying to use on both > TX and RX side are lower than the minimum sampling rates. You should > fix that. It’s not hard, you just need basic understanding of what the > program does. > To spell this out: the data rate together with the samples per symbol > define your sample rate. For your USRP, this rate must be at least > 250kS/s. The effect of you not correcting your flow graph is that the > script generates a signal that the USRP converts to an analog signal at > five times the speed that you specify – this means all frequencies with > your complex baseband are five times as high! > …U… Oh, that’s bad. You’re seeing an U like “Underrun”, which means your PC was too slow at supplying samples to the USRP. This seriously breaks your signal. Now, I don’t know your computer, but I know that 250kS/s is really no load for any PC nowadays – I haven’t seen any PC being too slow for this very low rate. How old is your PC? Are you doing something else on it? Or are you running in a virtual machine? > terminate > called after throwing an instance of ‘uhd::runtime\_error’ > what(): RuntimeError: usb tx2 transfer status: 1 > Aborted (core dumped). > That’s even worse. It can happen if you cancel the script using > “ctrl+c”, but this looks like there is something seriously wrong with > your USB2 controller. Again, what computer are you using? _Receiver_ > No gain specified. > Setting gain to 56.250000 (from [0.000000, 112.500000]) > The same as above. More gain = more signal power, but don’t overdo it. > You will need to experiment. As Tom explained, letting the transmitter > run and observing the spectrum with something like usrp\_spectrum\_sense > will help you determine settings that make sense. First, however, I can > not stress this enough, fix your sample rate issue! > Requested sample rate: 50000.000000 > Actual sample rate: 250000.000000 > The same as above. Both your RX and your TX are running at 250kS/s > instead of the 50kS/s that you specified. Luckily, this means that the > effect kind of cancels itself out – still, fix that! - General\* > How would I be able to know if the USRP is maintained in the same > channel? > You set both TX and RX to the same frequency, and since there is only > one physical medium (the space between the RX and TX antenna), you can > be sure. There’s no concept like “this specific part of spectrum belongs > to channel number 12” in the physical world – just frequencies, and > Maxwell’s Equations governing the propagation of radio waves. > What commands do I need to give so that the packet is received > correctly as n\_right=1. > Tom has explained enough that it’s not like that. You will need to find > out yourself. Best regards, Marcus PS: Do you have a preferred name to address you by? “Ravi” is as fine to me as “John”, so I’d suggest you pick one and stick with that, because it’s less confusing. [1] “Communication Problems between 2 USRP” email thread