Re: [Discuss-gnuradio] Signal Multiplication

[Eric Blossom]

On Sun, Nov 05, 2006 at 10:38:48PM -0500, Jonathan Shan wrote:
> On Sun, 5 Nov 2006, Eric Blossom wrote:
> 
> >I expect that your code is about 10 lines long.
> >Can you please post it?
> 
> Between the time of originally posting and now, I changed the length of 
> the vector and now am able to see a decent received signal.
> 
> The relevant code:
> 
>               src_data = (0,)*800 + (1,)*800
>                 vectordata = gr.vector_source_c(src_data, True)
>                 multiplier = gr.multiply_cc ()
>                 self.connect (adder, (multiplier, 0))
>                 self.connect (vectordata, (multiplier, 1))
>                 self.connect (multiplier, self.u)
> 
> adder is gr.sig_source_c(2000000, gr.GR_SIN_WAVE, 20000, 1000, 0).
> self.u is the usrp sink.
> 
> Now the amplitude of the sine wave appears modulated but it looks like the 
> frequency changes slightly which might make demodulating hard(?).
> 
> Example: 
> http://www.winlab.rutgers.edu/~jonshan/images/amlooptest2.dat.jpeg
> 
> Jonathan

What daughterboard are you using?
Have you set the the center frequency of the usrp?
If so, what frequency?
If you are outputting your signal with the Basic Tx set at 0 Hz, your 20kHz
signal is unlikely to get through the RF transformer.  Try setting the
the rf center frequency to 5 MHz and then look again.

Eric