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

[Activecat]

When I looked into the attached graphical flowgraph in the first email, the signal was multiplied by zero (constant multiplier) before feeding into file sink and audio sink.  In this case what you get was probably amplified noise.

Was it zero or something else?

On Fri, Apr 25, 2014 at 11:54 PM, Marcus Müller <address@hidden> wrote:

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A shoot, I overlooked the 64 decimation rate... Sorry about that.

On 25.04.2014 17:36, Anton Komarov wrote:
> Marcus, w/o AGC audio sometimes is creapy. I have tested AGC2,
> tried to play with attack and decay, but at last when there is a
> plane in the vicinity dongle overloads and sound become very loud.
> Then i tested FAGC and it fits well! 1024M/64 gives 16k and 256
> samples equals - 62 ms of signal. Works ok for me.
>
>
> On Fri, Apr 25, 2014 at 7:25 PM, Marcus Müller <address@hidden>
> wrote:
>

> Actually I'm a little confused - Is seeing an AGC in an AM
> demodulator something you usually do? Especially the feedforward
> AGC should be rather err jumpy with a scope of but 256 samples,
> unless I'm missing something; f_sample seems to be 1024ksps, thus
> 256 samples max search and rescaling should behave very badly if
> there are baseband signal contents below 4kHz -- and that should be
> the case for audio, usually?
>
> Greetings, Marcus
>
> On 25.04.2014 16:03, Marcus Leech wrote:
>>>> 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.
>>>>
>>>> -- public PGP key http://pastebin.com/dqZqgyVE
>>>>
>>>>
>>>> On Fri, Apr 25, 2014 at 5:11 PM, Michael Ossmann
>>>> <address@hidden <mailto: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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