Also, if you can describe the message flow in a little more detail, it would help. Is something sending a message to the number control, is the number control sending a message to something else, or both? If you are generating the message, make sure it is a double instead of a float. The number control is definitely generating a float, which can be shown to be wrong (same result as you reported):
>>> import pmt >>> pmt.to_double(pmt.from_float(138001000)) 138000992.0 On Sat, May 1, 2021 at 4:17 PM Jeff Long <willco...@gmail.com> wrote: > This is a buggy use of pmt.from_float() and/or pmt.to_float() in > digitalnumbercontrol.py. Please submit an issue to > https://github.com/gnuradio/gnuradio/issues and it will get fixed. > > On Sat, May 1, 2021 at 3:58 PM Marcus D. Leech <patchvonbr...@gmail.com> > wrote: > >> On 05/01/2021 10:37 AM, Tom Breyer wrote: >> > Dear team, >> > >> > when I use "QT GUI Digital Number Control" to display a frequency I see >> > some "special effects". >> > >> > Below 128MHz, it works fine but above I get wrong display data: >> > >> > ok: >> > Input 128.001.000Hz -> Display = 128.001.000 >> > >> > not ok: >> > Input 138.001.000Hz -> Display = 138.000.992 >> > Input 137.999.000Hz -> Display = 137.999.008 >> > >> > I simulate that input by using Gpredict via tcp port 4532 but found >> > debug messages ok. >> > >> > Does that depend on the QT GUI Digital Number Control and the way it >> > converts numerical data types, since (128 = 2⁷)? >> > Can I adjust that module by my own? >> > >> > 73, Tom, DJ6TB >> > >> > >> That's almost certainly an artifact of the machine representation of >> single-precision floating-point >> numbers. >> >> I'm not that familiar with the message infrastructure and whether it can >> carry double-precision values or not. >> [The sample streams within Gnu Radio are almost always >> single-precision floats, because; >> >> A: Computations in single-precision are considerably faster than >> double-precision >> B: There's no numerical advantage to double-precision for most >> signal-processing functions--there's more-than-adequate >> dynamic range in a single-precision (32-bit) representation. >> >> >> >> >> >> >>
