R820T vs. E4000

Al al at eartoearoak.com
Sun Mar 17 18:17:38 UTC 2013

Hi 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,


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

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