On 08/01/2012 04:07 PM, Christian Gagneraud wrote:
Hi all,
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?
Thanks,
Chris
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
work correctly.
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
frequencies-aren't-right issue.
--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
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