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Al al at eartoearoak.comHi Hunz, I've just pushed some updated code up to GitHub, you can now set the gain in the preferences and tweak the scan settings. There's some info at http://eartoearoak.com/software/rtlsdr-scanner#tweaking A 250kHz offset seems to work well with my E4000, 140k with a FC0012 and 100k with a R820T. The FC0012 is the noisiest and the R820T is quietest. Hope it helps, Al On 17/03/2013 11:00, Benedikt Heinz <zn000h at gmail.com> wrote: >> For me the most interesting plots were the "no antenna" ones, showing the LO >> leakage ;-) If I understood clearly your plots, you have at some places high >> power ghosts. Maybe you are close to powerful transmitters, but this is more >> probably a LO to RF isolation problem: the receiver receives himself... > I did two new measurements with the gain set to 20 in RTLSDR-Scanner. > The files with the -gain20 in the filename [1] show the new results. > There are more spikes from the R820T LOs now, but it's still less than > with the E4000 I'd say. > The good thing is that the DVB-T stations as well as some other > signals can be found as expected now. > > 2013/3/16 Al <al at eartoearoak.com>: >> I think you've run into a couple of issues, firstly it appears that the AGC >> isn't fully disabled on the R820T (if you remove the aerial the noise floor >> increases). > It looks like gain=0 just was too little for the R820T. gain=20 seems > to be a good start. > Maybe exposing the gain-value in the regular UI would make sense? > >> Secondly RTLSDR-Scanner averages 2 chunks of bandwidth either side of the DC >> point, these seem relatively quiet with an E4000 and FC0012 but I haven't >> had chance to check the R820T yet. This tuner may have a very different >> noise floor. I was wondering about adding a feature to allow the user to >> pick their own segments (by terminating the aerial and looking at the noise >> distribution). > Ah, that's interesting. I was indeed wondering how you avoid the DC > spike and my pathon skills are close to zero ;-) > According to [2], the R820T doesn't use a Zero-IF, so there should be > no DC-spike at all. > >> Has anyone had a chance to test 2 different dongles with the same tuner? >> I'd be interested to know if it makes a difference to the noise floor, if >> there is little change, I could vary the scan based on the tuner. > I do have two E4000 and two R820T dongles, but I haven't yet compared > the noise floor. > I'm thinking about a per-dongle baseline file w/o an antenna for > compensation. This approach should be more robust. Otherwise you need > to shift the baseline spectrum according to the frequency error. > > Best regards, > > Hunz > > [1] https://docs.google.com/folder/d/0ByDAKwyEiyx_XzZ5ZnpRV1VZWDQ/edit?usp=sharing > [2] http://lists.osmocom.org/pipermail/osmocom-sdr/2012-September/000253.html >