[time-nuts] timing and RTL-SDR

[jimlux]

the behavior of the inside of the 2832 downconverter isn't documented, 
although there's some theorizing that it's a complex I/Q multiply, 
followed by a FIR filter with 31 taps (which are published), followed by 
a resampler/decimator followed by a decimate by 4.

So I experimented with feeding in a step function to this and sliding it 
over.  10 MHz LO, 1 MHz output frequency (so the rational resampler is 
5/36).. I used Octave's resample() and decimate() and ran it floating 
point, so who knows if that's what the part actually does.  But, it does 
start to look like what I'm seeing.

I also (based on the discussion of Jim Palfreyman's quasar) doing a find 
the peaks do a linear fit and then stack.


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