Re: [Discuss-gnuradio] Waveform after AM demodulation looks weird

[Marcus Leech]

An AM demodulator is a squaring function.  It can only *ever* produce positive values.  You can remove DC offset by using a high-pass filter after it.

 

 

 

on Apr 25, 2014, Anton Komarov <address@hidden> wrote:

But when we have only positive values that means in fact we have 0.5 DC offset, and that is bad. Moreover i've made test recording with GQRX - waveform is fine! Looking into the code, nothing special, am demod->low-pass->wav-sink.

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public PGP key

http://pastebin.com/dqZqgyVE

On Fri, Apr 25, 2014 at 5:11 PM, Michael Ossmann <address@hidden> wrote:

On Fri, Apr 25, 2014 at 04:14:30PM +0400, Anton Komarov wrote:
>
> Hi, you can find in attach AM demodulator grc file. Everything is
> straight forward with demod but audio file generated looks weird. Only
> positive values of amplitude.

The particular definition of "amplitude" adopted by GNU Radio (and
pretty much everyone else in SDR as far as I know) is "absolute value".
It is correct for it to always be positive.

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