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/.
Stefan Sydow st at metafly.infoThe rtl-sdr (and all other software) has only a bandwidth of 3.2MHz maximum available. Only the hardware demodulator inside the realtek chip can process full 8MHz. If you consider the filter setting of the rtl-sdr you effective bandwidth is about 2 MHz. It is hard coded in the tuner code but reasonable for most settings, as it avoids aliasing. Am 06.07.2012 09:52, schrieb friedtj: > I am trying to implement equivalent time sampling using an EZCAP dongle configured using > gnuradio-companion. Since I am not completely clear about the tasks of the E4000 wrt RTL2832, > it could be that I am missing a significant information, so here is my experimental setup aimed > at developing a monostatic pulse mode RADAR : > * I am using a radiofrequency acoustic delay line to generate 4 echos delayed 1 to 2 microseconds > after an incoming excitation pulse is generated by a frequency synthesizer. The excitation pulse > is 125 ns long, and repetition rate is 4 microseconds. The carrier frequency at 860 MHz is chopped > by a fast duplexer, one side being connected to the frequency synthesizer and the other sizer to the > EZCAP dongle > * the EZCAP is configured with an LO at 860 MHz, 2 MS/s output, and I plot |I+jQ| after keeping > only 1 every 8 sample (2 MS/s=500 ns delay between samples, and 1 every 8 samples means a spacing > of 4 us, close to the emitted pulse repetition rate) > * equivalent time sampling is obtained by slightly tuning the emitted pule repetition rate off the > 4 us: I have checked that I can indeed obtain time stretching by tuning the pulse repetition rate > +/- 50 ns away from the 4 us dela, with time stretching factors of up to 10^5 (ie the 4 us pulses > are recorded as 400 ms traces (thus including 10^5 points or an equivalent sampling rate of 25 GS/s). > > Now of course a stretching factor of 10^5 is overkill and the RF front end definitely does not have such > a huge bandwidth, this is just to demonstrate the concept. With a more reasonable stretching factor of 10 (ie > sampling every 4.4 us with a 4 us emission pulse repetition rate), I can expect to convert a 2 MS/s sampling rate > to an equivalent time sampling of 20 MS/s, which would already improve my monostatic RADAR resolution by a factor 10, > and more or less fit my targetted resolution. > > So now the questions: > * the 125 ns pulse I generate would span 8 MHz. From my reading of the E4k description, this is within the > IF bandwidth available. However, although I can observe the emitted pulse (0 dBm), I cannot see the echos > (-35 to -40 dBm), whatever LNA gain I use (from 0 to 40 dB). Is the default configuration of the E4k an IF of > 8 MHz, or lower. What parameter should I give the rtlsdr gnuradio source block to make sure I have the right bandwidth ? > * since I am not clear about task distribution between the E4k and the RTL2832, is there another limitation that > will prevent a 8 MHz wide (bandwidth) signal to be recorded through the 2 MS/s I/Q output recorded ? The e4k does the filtering but has an analog output. The RTL2832 is in effect an USB ADC.