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Benedikt Heinz zn000h at gmail.com2013/3/15 Sylvain AZARIAN <sylvain.azarian at gmail.com>: > 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