Re: [Discuss-gnuradio] Single-tone test using USRP2 with RFX2400 and XCVR2450
On Fri, Aug 28, 2009 at 5:22 PM, Eric Blossom wrote: > If you're trying to send a sine wave, this will work much better: > (Generates a complex sinusoid == exp(jwt)) > > sig_source_c -> head -> usrp.sink_c > > Or you could use a hilbert transform to generate the quadrature > component. float_to_complex will be setting Q to zero the way you're > using it. Yes, setting Q to zero was the original idea. The whole point of using a sine wave was to have a better estimation of when the QAM signal actually started, but this "solution" gave me another problem to work on :) My question is why the received signal has sinusoidal components on both I and Q given that the wave has been "translated" to 2.5G (upon tx) and then back to DC (after the FPGA in rx). Should I not expect two impulses at +- 2M? Instead, what I get is a single impulse at aproximately -3kHz, regardless of the frequency set on the sig_source. > Eric > -- Igor Almeida ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] Single-tone test using USRP2 with RFX2400 and XCVR2450
On Fri, Aug 28, 2009 at 02:05:02PM -0300, Igor Almeida wrote: > On Fri, Aug 28, 2009 at 12:56 PM, Douglas > Geiger wrote: > > That sounds like it could be a frequency offset between TX and RX. You > > say you aren't synchronized (which I interpret to mean you don't lock > > the clocks of the TX and RX together somehow) - do you have a costas > > or similar carrier offset recovery block/process on your receiver? > > Correct, the USRPs are physically disconnected. > Right now, the graphs are: > > sig_source_f -> float_to_complex -> head -> usrp.sink_c If you're trying to send a sine wave, this will work much better: (Generates a complex sinusoid == exp(jwt)) sig_source_c -> head -> usrp.sink_c Or you could use a hilbert transform to generate the quadrature component. float_to_complex will be setting Q to zero the way you're using it. > usrp.source_c -> file_sink (on the other PC) > > TX usrp sends the first 1000 cycles of a 2MHz sine wave (sig_source > with 4MS/s), then the "training graph" is disconnected and another one > with the QAM modulator kicks in. Both scripts tune to 2.5G. > The strange thing is no matter what frequency I set the sig_source to > (already tried 1.5k, 2k, 1M and 2MHz, sampling frequency 4MS/s), the > fft on matlab always shows a single impulse at aproximately -3kHz. In > the time domain, the signal is sinusoidal on both real and imaginary > parts, when I expect it to be only real since the carrier has (should > have) been removed. > > I believe I am missing some trivial concept here. See above. Eric ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] Single-tone test using USRP2 with RFX2400 and XCVR2450
On Fri, Aug 28, 2009 at 12:56 PM, Douglas Geiger wrote: > That sounds like it could be a frequency offset between TX and RX. You > say you aren't synchronized (which I interpret to mean you don't lock > the clocks of the TX and RX together somehow) - do you have a costas > or similar carrier offset recovery block/process on your receiver? Correct, the USRPs are physically disconnected. Right now, the graphs are: sig_source_f -> float_to_complex -> head -> usrp.sink_c usrp.source_c -> file_sink (on the other PC) TX usrp sends the first 1000 cycles of a 2MHz sine wave (sig_source with 4MS/s), then the "training graph" is disconnected and another one with the QAM modulator kicks in. Both scripts tune to 2.5G. The strange thing is no matter what frequency I set the sig_source to (already tried 1.5k, 2k, 1M and 2MHz, sampling frequency 4MS/s), the fft on matlab always shows a single impulse at aproximately -3kHz. In the time domain, the signal is sinusoidal on both real and imaginary parts, when I expect it to be only real since the carrier has (should have) been removed. I believe I am missing some trivial concept here. -- Igor Almeida ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] Single-tone test using USRP2 with RFX2400 and XCVR2450
On Fri, Aug 28, 2009 at 11:09 AM, Igor Almeida wrote: > > I [believe I] am having a similar problem with USRP rev4 and RFX2400. > Sending a QAM-modulated signal in a 2.5GHz carrier with no > synchronization gives me a lot of background noise before the actual > signal. So I am prepending a 2MHz sine wave in a separate block, > executed prior to the QAM modulation, but I cannot find the impulses > in +- 2M after the receiving USRP downconverts it from 2.5GHz. > The part of the signal which is supposed to contain the 2M wave shows > both real and imaginary sinusoidal signals, always close to DC by 3k > Hz or so. Am I missing anything? > > -- > Igor Almeida That sounds like it could be a frequency offset between TX and RX. You say you aren't synchronized (which I interpret to mean you don't lock the clocks of the TX and RX together somehow) - do you have a costas or similar carrier offset recovery block/process on your receiver? -- Doug Geiger doug.gei...@bioradiation.net ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] Single-tone test using USRP2 with RFX2400 and XCVR2450
On Fri, Apr 24, 2009 at 12:30 AM, Yongsang Kim wrote: > Hi, all. > > I did single-tone test using USRP2 with RFX2400 and XCVR2450. > There are some undesired signals in the results. > > My single-tone test is as follows: > - Wired connection between USRP2 and Spectrum analyzer > - Single-tone is transmitted from USRP2 using the following commands > ./usrp2_siggen.py -f > ./usrp2_siggen.py -f -w > - For daughter board, RFX2400, XCVR2450 and Basic TX are tested > - Newest GNU radio and firmware I [believe I] am having a similar problem with USRP rev4 and RFX2400. Sending a QAM-modulated signal in a 2.5GHz carrier with no synchronization gives me a lot of background noise before the actual signal. So I am prepending a 2MHz sine wave in a separate block, executed prior to the QAM modulation, but I cannot find the impulses in +- 2M after the receiving USRP downconverts it from 2.5GHz. The part of the signal which is supposed to contain the 2M wave shows both real and imaginary sinusoidal signals, always close to DC by 3k Hz or so. Am I missing anything? -- Igor Almeida ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] Single-tone test using USRP2 with RFX2400 and XCVR2450
Yongsang Kim wrote: Hi, all. I did single-tone test using USRP2 with RFX2400 and XCVR2450. There are some undesired signals in the results. My single-tone test is as follows: - Wired connection between USRP2 and Spectrum analyzer - Single-tone is transmitted from USRP2 using the following commands ./usrp2_siggen.py -f ./usrp2_siggen.py -f -w - For daughter board, RFX2400, XCVR2450 and Basic TX are tested - Newest GNU radio and firmware - PC specification (I'm pretty sure that the spec is good enough to transmit single-tone stably) -- CPU: Intel core2quad processor Q9550 -- Ethernet card: Intel 82567LM Gigabit LAN (PCI express slot) -- Memory: 4GB DDR2 800 MHz SDRAM memory Except the case of Basic TX, there are some undesired signals in the results. So, I guess the undesired signals are generated by RFX2400 and XCVR2450, not by mother board. I'm afraid that the undesired signals cause some kind of distortion of desired signal. (In fact, when I transmit OFDM signal using XCVR2450, I fail to demodulate the received OFDM signal) The resulting spectrum figures are shown in the following link and I marked the undesired signals in the figures. What you are seeing are normal transmitter non-idealities, including DC offset (aka carrier feedthrough), and IQ imbalance (aka sideband suppression. These can be improved through tuning, but they are not bad as is. Also, on the XCVR you are seeing the phase noise skirts as well. Matt http://141.223.23.5/Spectrum.zip Short descriptions for each figures are as follows: 1. File name: RFX2400_2p375GHz_01 Used daughter board: RFX2400 GNU radio command: ./usrp2_siggen.py -f 2.375e9 2. File name: RFX2400_2p375GHz_02 Used daughter board: RFX2400 GNU radio command: ./usrp2_siggen.py -f 2.375e9 -w 2M 3. File name: XCVR2450_2p52GHz_01 Used daughter board: XCVR2450 GNU radio command: ./usrp2_siggen.py -f 2.52e9 4. File name: XCVR2450_2p52GHz_02 Used daughter board: XCVR2450 GNU radio command: ./usrp2_siggen.py -f 2.52e9 -w 2M 5. File name: BasicTX_30MHz_01 Used daughter board: Basic TX GNU radio command: ./usrp2_siggen.py -f 30e6 6. File name: BasicTX_30MHz_02 Used daughter board: Basic TX GNU radio command: ./usrp2_siggen.py -f 30e6 -w 2M I would appreciate that if somebody let me know what is problem of my daughter boards or my test. Thanks. ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
