Hi Marcus, How can (or better: *should*) a fully digital signal source have phase noise?
Also, for 1Hz at 5MSps I always get either 5005789 or 5005790 samples (instead of 5000000) ... this is fairly deterministic. Experimenting a bit, I see the weirdest behaviour of the analog signal source. In my opinion, the source should be fully deterministic. But it is not. Example 1: I pipe the output of the signal source into a file: https://snipboard.io/xY1JvE.jpg and read it with MATLAB: data = read_float_binary('baszmeg.dat'); Then I compare it to an ideal (=expected) version: t = 0:1/fs:(length(data)-1)/fs; plot(t, [data - sin(2*pi*t)' ]) https://snipboard.io/ecTaFL.jpg Now, I would not care too much about a constant phase shift or similar, but it can be seen that the frequency slowly drifts (this is also seen if I just plot them on top of each other). Example 2: I extend the block diagram with blocks that should never alter the behaviour as they are only reading samples: https://snipboard.io/W6kyF0.jpg Note that the "Controller" is a simple Embedded Python block that only reads the input samples into a temporary variable: def work(self, input_items, output_items): squared_wave = input_items[0] squared_wave[np.where(input_items[0] > 0)] = 1 output_items[0][:] = input_items[0] return len(output_items[0]) However, now the saved data is distorted: https://snipboard.io/amyn3X.jpg Any suggestions highly appreciated. Thanks, Lukas > Gesendet: Mittwoch, 26. Februar 2020 um 16:39 Uhr > Von: "Marcus D. Leech" <patchvonbr...@gmail.com> > An: "Lukas Haase" <lukasha...@gmx.at> > Cc: "discuss-gnuradio@gnu.org" <discuss-gnuradio@gnu.org> > Betreff: Re: How ensure consistency with timing signals > > On 02/26/2020 04:11 PM, Lukas Haase wrote: > > Hi Marcus, > > > > Good point; but this is just for demonstration purposes here. I can tie it > > to USRP Source/Sink. > > > > The delta (measured in samples) should still be consistent, no matter what. > > > > Best, Lukas > > > > > Looking at the siggen code, this is probably equivalent to phase-noise > in the generator. The square wave outputs are derived from COS/SIN, and > at such a high ratio between sample rate and frequency, there'll be a > bit of phase noise. > > Someone with more knowledge of the siggen block can comment further. > > >
