Re: [Discuss-gnuradio] New to gnuradio - Complex sampling question - urgent

[Peng Huo]

Ok, I understand. To convert this complex signal to a real, one has to do this according to the following formula, isn't it?

x(t) = X(t)Cos(2*pi*fc*t) - X(t)Sin(2*pi*fc*t) where X(t) -> Complex signal, fc -> Carrier frequency, x(t) -> real signal.

I looked at the block "complex_to_real" and it outputs the Inphase component as the real signal. Is it because, "fc" is 0Hz as the signal being at baseband? I think this sounds right.

I want to mulitply a real signal with a PN sequence and then pass the result on to a costas loop which takes a complex input. I want to know how can we get a complex signal from a real one. Is there a block that does that? 

Thanks
Peng

On Fri, Jun 12, 2009 at 10:50 AM, Jordan J Riggs <address@hidden> wrote:

If I understand correctly, the real signal picked up by the antenna is mixed with two sine waves, 90 degrees out of phase, to create the I and Q components at baseband (depending on the daughterboard, there may be an intermediate frequency involved). The I and Q signals are then sampled by the ADCs. I and Q are then interleaved and sent over USB.
See page 9 of the USRP FAQ for more info.
http://www.scribd.com/doc/9688095/USRP-Documentation

Jordan

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