Forum: GNU Radio Rectifying and Low Pass filter

53a1f0aba6f0489d49f5e6fc3df323fa?d=identicon&s=25 Robert James (robertjames)
on 2013-11-17 20:02
(Received via mailing list)
I'm trying to demodulate AM (I know there are existing blocks to do
that, but I'd like to learn how to do it on my own).

In a real world analog circuit, I would find the envelope by first
rectifying the signal (using a diode), and then using a low pass
filter - that would give me the envelope.

How can I rectify with GNU Radio?
D3e3c5e41e9aed486856802be823e181?d=identicon&s=25 Johnathan Corgan (Guest)
on 2013-11-17 20:26
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53a1f0aba6f0489d49f5e6fc3df323fa?d=identicon&s=25 Robert James (robertjames)
on 2013-11-17 20:54
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I see.  For those of us who have some background in analog circuits,
is there a way to work with real valued passband signals? For example,
is there a block which takes a complex baseband signal and converts it
to a real valued passband signal?
C539637020fd56193dd6daec746c4a84?d=identicon&s=25 Tom Rondeau (Guest)
on 2013-11-17 22:17
(Received via mailing list)
On Sun, Nov 17, 2013 at 2:53 PM, Robert James <srobertjames@gmail.com>
wrote:
> I see.  For those of us who have some background in analog circuits,
> is there a way to work with real valued passband signals? For example,
> is there a block which takes a complex baseband signal and converts it
> to a real valued passband signal?

You can always go through a type converter block "complex to float"
which outputs a stream for the real and (if connected) the imaginary.
Or you can just use the "complex to real" block to just get the real
part.

However, and I'm not trying to be glib or insulting, the best thing to
do is really to understand how to work at complex baseband. When
working with software radio, we're not just doing in software what we
did in analog circuits. Sometimes we do, sometimes it looks similar,
but by working in the digital domain, we're changing a lot about how
we work with signals. In many ways, we're now able to more accurately
represent the real mathematics of signal processing where we were only
approximating it in hardware.

Tom
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