Multiply block problem in GRC 3.6.5.1

GNU Radio
1

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.
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
Sorry for my bad english.
Best regards

Att.:
Winderson Luiz Franzoi Speranzini

2

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 R. http://switchb.org/kpreid/

3

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