Re: [Discuss-gnuradio] ASK demodulation help

Depending on various factors the implementation may vary, but you could probably start with a chain that looks something like this:

I/q source -> filter -> AGC -> AM demod (complex to mag) -> scaling for am depth -> m&m clock recovery -> slicer -> do something with the data

Other, more advanced implementations might use correlation for synchronization.

-John

On Wed, Apr 9, 2014 at 1:27 PM, Francois Gervais <francoisgervais@gmail.com> wrote:

Hi,

I'm new to gnu radio and I'm trying to demodulate a 125kpbs ASK signal from a device I have, as a first project. I'm using RTL-SDR as the input device.

I'm slowly getting there. I receive the signal, at 2Msample/s, I low-pass filter it to 300khz, I send it through the AM demodulation block and then through the DC blocker. 

From there I have my signal and it looks fine i.e I could retrieve the information manually by looking at it. 

Now I think the goal is to somehow synchronize with the bits and re-sample to get 1 sample per bit. This could then be sent to a file. Is that it?

At first glance I'm thinking I should have a PLL which ouputs a clock at about 250khz (twice the bit rate) and synchronize the rising edge with every bit transitioning from 0 to 1 so unless I receive only ones ou zeros I should be quite in sync. Then I could toggle a sample every falling edge of the clock which should be at about the middle of the bit. 

Is this a viable solution? Can it be done with gnuradio? Other alternatives?

Thanks

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