This is merely a historical archive of years 2008-2021, before the migration to mailman3.
A maintained and still updated list archive can be found at https://lists.osmocom.org/hyperkitty/list/osmocom-sdr@lists.osmocom.org/.
Michael Karcher osmosdr at mkarcher.dialup.fu-berlin.deAm Dienstag, den 20.08.2013, 14:24 +1000 schrieb David Basden: As far as I understand it, sampling really happens at 28.8MHz with probably 8 bits per channel. These ADCs are integrated in the RTL2832U chip. After sampling, the samples are filtered using a symmetric FIR filter (I reported how that filter is programmed around a year ago on this list), then resampled to four times the user ADC. At that stage, a second FIR anti-alias filter which seems ot be fixed (or running on default coefficients all the time) kicks in before down-sampling to the requested sample rate. The 7-bit ADC quoted by jdow is also present on the chip, but it is a low-bandwidth ADC. Some tuner chips, like the FC0012 (one of my dongles has that chip) have a wide-bandwidth rectifier indicating the total RF level at the input, but only an analog output but no digital provision to read that level. The 7-bit ADC is used to measure the RF level to set the RF gain for the tuner. The 3.2MSps limit is definitely caused by the USB interface in the RTL chips, actually, in my experience, already 2.88MHz is sometimes dropping samples. It seems (from comments in the vendor-provided DVB-T driver) like there might be a way to run that chip in USB isochronous mode instead of bulk mode, but I have no idea whether that would require strap modification, or just fiddling with some registers in the USB interface section. > On Mon, Aug 19, 2013 at 08:47:20PM -0700, jdow wrote: > > That doesn't necessarily square with "7-bit ADC for RF signals level > > measurement". It's unclear to me where it would get the signal with > > enough levels that a 7-bit ADC would get used. You'd have to decimate > > down to 225 Msps or so in order to get 7 bits of data. > > > > {^_^} Joanne/W6MKU Regards, Michael Karcher