Multiplying 2 signals from the grc

GNU Radio
1

Hi all,
I need to multiply 2 signals (800 MHz and 820 MHz) from external signal
generators. I used the usrp-1 and DBSRX daughter-boards to detect the 2
signals. I attached the grc file that I created for this application. I
can detect signal from the output of the usrp source.

When I multiply, I expect to have 2 components (sum and difference) at
20 MHz and 1.620 GHz. To visualize these 2 components, I need to set the
FFT-sink to display a wide range. This means the FFT sink sample rate
must be high i.e 3.4 G. With this value, the FFT doesn’t display the
plot. I used a Rational Resampler to match the usrp source sample rate
with the FFT sample rate. But it’s still not working.

Can anyone tell me how to fix this. Your help will be appreciated.
Dominique
Regards.

2

On Fri, Apr 6, 2012 at 2:04 AM, guelord ingala
[email protected]wrote:

used a Rational Resampler to match the usrp source sample rate with the FFT
sample rate. But it’s still not working.

It is working, but you have a misunderstanding of how the USRP and
Gnuradio
work. The DBSRXs downconvert the 800 and 820MHz signals to baseband
(0Hz)
and then the USRP digitizes them and brings them to Gnuradio. You are
effectively multiplying two 0Hz signals. You cannot mix RF signals in
Gnuradio, only baseband signals. In the same way, a sample rate of
3.4Gsps
does not make sense.

–n