Forum: GNU Radio Complex-->real

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Marcus D. Leech (Guest)
on 2009-02-16 00:51
(Received via mailing list)
I have a complex stream that I've bandpass filtered so that it only
contains the positive frequencies.  I want to turn this into
  a real signal.  In the reverse direction, you use a hilbert transform,
right?  But how do you do it in the reverse direction?
  Do I just do a complex-to-float, and take the one that's "real", and
ignore the other one?

Left his complex arithmetic brain in his other pants....

--
Marcus L.
Principal Investigator, Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
Martin B. (Guest)
on 2009-02-16 10:27
(Received via mailing list)
On Sun, Feb 15, 2009 at 05:50:24PM -0500, Marcus D. Leech wrote:
> I have a complex stream that I've bandpass filtered so that it only
> contains the positive frequencies.  I want to turn this into
>   a real signal.  In the reverse direction, you use a hilbert transform,
> right?  But how do you do it in the reverse direction?
>   Do I just do a complex-to-float, and take the one that's "real", and
> ignore the other one?

You can do that, or use gr_complex_to_real() which I would prefer for
coid readability. In my textbooks, the baseband to passband relation is
often described as

s(t) = Re{ x(t) exp(j 2 pi fc t) }

which is exactly what you'd be doing then (x(t) being the complex
baseband signal).

Cheers,
MB
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