An LO offset tunes the analog hardware to desired_freq+LO_offset, and
then digitally basebands the desired frequency. However, if the analog
bandwidth is narrow enough that the digital basebanding (DDC) doesn't
have any useful signal, then this will be the result.
On 2017-08-25 12:47, Jacob Knoles wrote:
> Thanks.
>
> I didn't expect the actual input to shift with the LO offset.
>
> -----------------------------
> Jacob Knoles
>
> On Fri, Aug 25, 2017 at 9:08 AM, <mle...@ripnet.com> wrote:
>
> That's probably because you set your bandwidth to be somewhat narrow, so with
> offset tuning, you were only seeing the deeply-filtered data.
>
> On 2017-08-25 11:23, Jacob Knoles wrote:
> I found my issue. When I set my center frequency to monitor I also provided a
> LO offset. The intention is to not have the LO included in the response.
>
> For some reason it seams this pulled the receive frequency with it. By
> removing the LO offset I am getting the data I expect to see.
>
> At this time I am not sure why this is happening?
>
> -----------------------------
> Jacob Knoles
>
> On Fri, Aug 25, 2017 at 8:12 AM, Jacob Knoles <knole...@gmail.com> wrote:
>
> The numbers coming out are essentially zero. Looking at the chart it reads
> -1.3e-17. There are a lot of values that do come out exactly zero, as they
> become -inf (or something like -370) after going through the log10
> mathematics.
>
> The signal I am inputting however is a simulated BT signal with the peak at
> -40 dBm and modulated. At the one frequency I am monitoring it results in a
> square wave. So I expect to see a distinct change in the output numbers.
>
> -----------------------------
> Jacob Knoles
>
> On Thu, Aug 24, 2017 at 6:15 PM, Marcus D. Leech via USRP-users
> <usrp-users@lists.ettus.com> wrote:
>
> On 08/24/2017 08:11 PM, Jacob Knoles via USRP-users wrote:
>
> Hello,
>
> I am trying to do a simple receive function that grabs data for 12 seconds,
> calculates the log10 power and then plots power vs time.
>
> I am using the GnuRadio C++ API and have done a prototype using GnuRadio
> Companion. I am also feeding in a dummy signal using a vector signal
> generator.
>
> While running the Companion code I get exactly the results I expect to get,
> as seen in this image:
>
> The top time plot is displaying each step of the calculation chain, Red is
> the real part of the complex number, green is the imaginary part and blue is
> the magnitude.
>
> The lower plot shows the power vs time trace that I am after for this test,
> the calculation being used is 20*Log10(mag) - 17.
>
> The offset was calculated by comparing a known signal on a spectrum analyzer.
>
>
> So now my issue. When I take this prototype and implement it in C++ (that is
> what my program is using) I do not get any results back at all.
>
> Here is the C++ resulting plot of the real complex values only:
>
> As can be seen all the values are essentially zero.
>
> Here is the code snippet that is handling the capture, it returns a
> std::vector<float> which is plotted elsewhere in the software. (I have
> confirmed that the plotting software is not the issue.)
>
> _rate = 5e6;
> //--------------------------------------------------------------------------------
>
> //-- Make a top block
> //--------------------------------------------------------------------------------
>
> auto tb = gr::make_top_block( "TraceCapture" );
>
> //--------------------------------------------------------------------------------
>
> //-- make the usrp
> //--------------------------------------------------------------------------------
>
> auto stream_args = uhd::stream_args_t( "fc32", "sc16" );
> stream_args.channels.push_back( 0 );
> auto usrp_source = gr::uhd::usrp_source::make( uhd::device_addr_t( "" ),
> stream_args );
> usrp_source->set_samp_rate( _rate );
> usrp_source->set_center_freq( uhd::tune_request_t(carrier_freq, 10e6) );
> usrp_source->set_gain( _gain_one );
> usrp_source->set_bandwidth( 1e6 );
> usrp_source->set_antenna( "RX2" );
>
> //--------------------------------------------------------------------------------
>
> //-- Make the necessary flowgraph blocks
> //-------------------------------------------------------------------------------
>
> auto complex_to_mag_sptr = gr::blocks::complex_to_mag::make( );
> //auto nlog10_sptr = gr::blocks::nlog10_ff::make( 20, 1, -17.4 );
> auto vector_sink_sptr = gr::blocks::vector_sink_f::make( );
> auto complex_to_real_sptr = gr::blocks::complex_to_real::make( );
>
> //--------------------------------------------------------------------------------
>
> //-- Connect the flowgraph
> //--------------------------------------------------------------------------------
>
> //tb->connect( complex_to_mag_sptr, 0, nlog10_sptr, 0 );
> //tb->connect( nlog10_sptr, 0, vector_sink_sptr, 0 );
> //tb->connect( complex_to_mag_sptr, 0, vector_sink_sptr, 0 );
> tb->connect( complex_to_real_sptr, 0, vector_sink_sptr, 0 );
> tb->connect( usrp_source, 0, complex_to_real_sptr, 0 );
>
> tb->start( );
> std::this_thread::sleep_for( std::chrono::milliseconds( static_cast<long
> long>( capture_time * 1000 ) ) );
>
> tb->stop( );
> tb->wait( );
>
> return std::make_shared<std::vector<float>>( vector_sink_sptr->data( ) );
>
> When I run the code on my B210 I get no errors, the RX2 led lights as
> expected, all the numbers get calculated as expected yet no matter what I
> have tried I am getting only zeros from the B210
>
> Additionally I am working on Windows 10 with VS 2015. I have installed a
> binary version of GnuRadio. Here is the flowgraph in grc for reference as
> well.
>
> Any help will be greatly appreciated!!
>
> Thanks
>
> -----------------------------
> Jacob Knoles
>
> _______________________________________________
> USRP-users mailing list
> USRP-users@lists.ettus.com
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com [1]
>
> Do you mean "essentially zero" or actually zero? There's a difference.
>
> _______________________________________________
> USRP-users mailing list
> USRP-users@lists.ettus.com
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com [1]
Links:
------
[1] http://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
