17 Mar
2013
17 Mar
'13
7:17 p.m.
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,
Al
On 17/03/2013 11:00, Benedikt Heinz <zn000h(a)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(a)eartoearoak.com>om>:
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=shar…
[2] http://lists.osmocom.org/pipermail/osmocom-sdr/2012-September/000253.html