# Signal Multiplication

Hello all,

I am new to gnuradio and communication theory.

I am trying to multiply two signals by their corresponding elements. I
am
trying to mimic amplitude modulation.

I already have source1 which is a sine wave generated by sig_source_c.
There is source2, which is a vector source generated by vector_source_c.
I
can confirm that both these sources are “correct” individually, but when
I
try to multiply them by doing multiply_cc, weird stuff happens.

Example is if I set the vector to all zeroes, I expect the output of
multiplier to be all zeroes. This is not the case.

Thanks,
Jonathan

On Sun, Nov 05, 2006 at 01:47:45PM -0500, Jonathan Shan wrote:

try to multiply them by doing multiply_cc, weird stuff happens.

Example is if I set the vector to all zeroes, I expect the output of
multiplier to be all zeroes. This is not the case.

Thanks,
Jonathan

I expect that your code is about 10 lines long.
Can you please post it?

Eric

On Sun, 5 Nov 2006, Eric B. 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(?).

Jonathan

On Sun, Nov 05, 2006 at 10:38:48PM -0500, Jonathan Shan wrote:

``````  src_data = (0,)*800 + (1,)*800
``````

frequency changes slightly which might make demodulating hard(?).

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