Oh, thank you friend for this quick reply. I will do what you said By the way, where can I find the blocks source codes? Thank you again!
Att.: Winderson Luiz Franzoi Speranzini > Subject: Re: [Discuss-gnuradio] Multiply block problem in GRC 3.6.5.1 > From: [email protected] > Date: Thu, 27 Mar 2014 16:17:46 -0700 > CC: [email protected] > To: [email protected] > > On Mar 27, 2014, at 15:10, Winderson Luiz Franzoi Speranzini > <[email protected]> wrote: > > > Hello GRC community, > > I'm initiating with grc, trying to make a simple BASK. I searched a lot in > > the mailing list and in the tracker (I don't know if it's called that way) > > but I was unable to find anything about. It's a simple problem (maybe due > > my GRC version) that does not ruin my projects at all. > > When I use the multiply block, inputing a cossine(12kHz) and a > > rectangular(1kHz) wave from the signal generator block, I don't get the > > nice BASK that we should (Viewed from a wx osciloscope). Instead, the > > cossine change the amplitude in the middle 3 cycles and last longer 3 other > > cycles than it should. > > I wasn't sure myself what a complex square wave actually ought to be, so I > took a look at the source code and found this statement: > > /* Implements a real square wave high from -PI to 0. > * The imaginary square wave leads by 90 deg. > */ > > This would explain your observation, I think: the complex square wave > provided by GR is zero only 1/4 of the time. It probably isn't what you want. > > > The fact is that it just happen when I use complex outputs and inputs. Both > > the I and Q wave have the same style. When I use real inputs, or if I > > separete the real and imag part, multiply they separately and then put > > together in a complex signal, it works like it should be. Maybe it can be > > an old and corrected bug > > GR's multiply_cc block follows the rules of complex arithmetic as it should. > Complex multiplication is not component-wise multiplication. > > To get the result I think you had in mind, then you should multiply the > complex sinusoid by a _real_ square wave. That is, set your square wave > signal generator to have a float output, convert the output to complex > (leaving the imaginary input unconnected, implicitly zero), then multiply it > with the sine. > > -- > Kevin Reid <http://switchb.org/kpreid/> >
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