[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Discuss-gnuradio] Do RTL based devices need some sort of calibratio
Marcus D. Leech
Re: [Discuss-gnuradio] Do RTL based devices need some sort of calibration?
Wed, 01 Aug 2012 16:32:55 -0400
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:22.214.171.124) Gecko/20111108 Fedora/3.1.16-1.fc14 Thunderbird/3.1.16
On 08/01/2012 04:07 PM, Christian Gagneraud wrote:
Are you perhaps trying to run your RTL device at some weird sample
rate? The device really only supports sample rates from 1Msps to about
2.8Msps, and only a few of those rates have actually been verified to
I've been using a FCD for a couple of weeks now and I decided to get a
go with a rtl-sdr compatible dongle. I bought one from osmocom and I'm
having trouble to get useful data out of it.
Based on the USB IDs, this is a "Generic RTL2832U (e.g. hama nano)".
Basically my problem is that the frequencies are wrong, first there's
a big offset (that can be fixed using the freq. corr. ppm), but i have
as well a scaling issue. When I'm looking at AIS signal i should see 2
blobs 25Khz apart of the center frequency (162MHz), but when i'm using
the RTL source the 2 blobs are separated by ca. 20KHz, instead of 50KHz.
As a quick test, i set up 2 osmosdr sources (one with dev set to fcd=0
and the other rtl=0, they have the same freq and rate settings) and I
plotted their FFT. The FCD is working as expected, but for the RTL,
the 2 blobs are way closer the the central frequency.
So my question is does this device need some extra special settings?
Is there any documentation about all the settings i can use? Should I
calibrate it using some special technique, or does that simply mean
that this particular device is just non functional?
My suspicion is that you're trying to run it at a rate it doesn't really
support. Try 1.0Msps or 1.024Msps and see if that clears up your
Shirleys Bay Radio Astronomy Consortium