Hi Marcus, How do i produce a sum of multiple tones using the uhd libraries? tx_waveforms.cpp lets me set a center frequency with uhd::tune_request_t tune_request(LO_freq), but what I want is to see an output A1*sin(f1*t + phi1) + A2 * sin(f2*t + phi2) + ...
Along similar lines, how do I change the amplitudes and phases of each waveform from the uhd libraries? When you say fiddle with the iq corrections, I can do that from within radio_legacy.v, correct? Thanks for the help, I'm fairly new to SDR. On Sat, Oct 14, 2017 at 8:30 AM, Marcus Müller via USRP-users < usrp-users@lists.ettus.com> wrote: > Hi Oliver, > > haven't quite thought through an understanding of what you're currently > doing, but: > > Since the FPGA image already comes with a convenient-to-use DUC – why not > just produce a constant, and tune digitally to a non-zero frequency? That > way, the CORDICs inside the duc_chain will simply generate your sine for > you, presumably at a much higher resolution than your 1024 element sine > table, for free. > > To test: use your PC to send a constant, use a > uhd.tune_request_t(LO_frequency+tone_frequency, > tone_frequency). > > If there's still a LO leakage on the output, you can manually fiddle with > the IQ corrections inside the AD9361. > > Best regards, > > Marcus > > On 12.10.2017 02:23, Oliver Wayne via USRP-users wrote: > > Hello, > > I've implemented a DDS signal on the USRP device. In radio_legacy.v, I > input get_tx_I and get_tx_Q as my I and Q channels. > always @(posedge radio_clk) begin tx[31:16] <= (run_tx) ? > get_tx_I[31:16] : tx_idle[31:16]; // I channel tx[15:0] <= (run_tx) ? > get_tx_Q[31:16] : tx_idle[15:0]; // Q channel end These are 32 bit > registers and I calculate the value of get_tx_I and get_tx_Q in external > modules. Currently I use 10 bit registers in my sine lookup table, so > something like > > sine[0] = 340; > sine[1] = 342; > ... > And I sum several of these sine terms, then set get_tx_I(Q) equal to their > sum. The problem is this has a DC offset, which means that that the local > oscillator signal also shows up in my spectrum, which I don't want. When I > try to kill the DC offset, so I write > > sine[0] = 0; > sine[1] = 1; > ... > > Then I still get a local oscillator term, but also get garbage in the > spectrum. What's the optimal way to remove a DC offset? I was not sure > whether I should explicitly write out the negative value as two's > complement in the lookup table, or use something like > https://files.ettus.com/manual/classuhd_1_1usrp_1_1mult > i__usrp.html#a263ab7f0364c03e8a6e330c546769e4f. > > thanks > > > _______________________________________________ > USRP-users mailing > listUSRP-users@lists.ettus.comhttp://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > >
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