RTL-SDR sample bit depth
John Ackermann N8UR
jra at febo.com
Fri Mar 2 14:46:41 UTC 2018
I'm trying to understand the sampling and decimation structure of the
RTL-SDR dongle, to work out the effective number of bits after decimation.
From Google and looking at the librtlsdr code (which is beyond my
programming depth), I think I've figured out the following. I'd much
1. Actual ADC in the RTL-2832U is a single-bit sigma-delta running at
some very high rate.
2. This is converted to 28.8 msps at 8 bit depth.
3. 28.8 msps is downsampled to the rate requested by the user and sent
over the USB bus as 8 bit unsigned IQ pairs.
Based on that, I *think*:
a. Any processing gain in the downsample from 28.8 msps/8 bits within
the chip is lost because the wire samples are limited to 8 bits. The
output is 8 bits dynamic range regardless of the sample rate set.
b. THEREFORE... for best dynamic range one wants to set the RTL-2832U
to the highest sample rate that avoids lost samples, and do further
decimation in the host processor, where the added bits aren't lost on
I'd appreciate any verification or correction of that analysis.
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