Incorrect samplerate from RTL-SDR

Joris van Rantwijk joris at jorisvr.nl
Sun Jan 5 17:04:01 UTC 2014


Hi Steve,

Thanks for your quick answer.

On 2014-01-05, Steve Markgraf wrote:
> We could return some sort of error in those cases, but such low rates
> (< 1MS/s) aren't recommended in general.

If you know that the hardware is going to freak out, I think returning
-EINVAL is a more useful thing to do.

Normally I expect a function to either do what it promised or return an
error. Because RTL-SDR is reverse-engineered, it is not fair to judge
it to such high standards. Still, it would be good to document known
limitations of the RTL chip in the library via comments or error codes.

> First of all, the
> anti-aliasing filter we're using has a fixed bandwidth of 2 MHz, and
> although the coefficients can be changed, I doubt you can get a nice
> filter for lower bandwidths with such a low order. And then the ADCs
> only have 8 bits resolution, so you want to improve that by
> decimating, and also profit from decimation gain.

That is good to know. So in general I should try to keep the hardware
sample rate high, and resample in software if needed.

Thanks,
Joris.




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