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Richard Koch n1gp at hotmail.comHi Steve, In regards to your post about the anti-aliasing filter you referred to, it appears that it is getting set in librtlsdr.c, rtlsdr_init_baseband() If one wanted to change that to optimize the anti-aliasing to a lower bandwidth, say 1500 Khz instead of the 2048 Khz How would you change the fir_coeff[] table entries to achieve this? The 8 bit entries and 12 bit entries are confusing to me. ==== orig post ==== > I have seen other reports on the mailing list, saying that sample rates > between 300 kS/s and 900 kS/s don't work. If this applies to all RTL > devices, then maybe it should be documented and the library can return > an error code for such sample rates. Otherwise people will keep walking > into this trap. We could return some sort of error in those cases, but such low rates (< 1MS/s) aren't recommended in general. 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. Even Realtek uses 2.048 MS/s for FM reception in their original Windows software. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.osmocom.org/pipermail/osmocom-sdr/attachments/20140109/9eef9131/attachment.htm>