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Re: [Discuss-gnuradio] Problem converting RTL 8 bit IQ samples to gnurad


From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] Problem converting RTL 8 bit IQ samples to gnuradio native format.
Date: Wed, 19 Dec 2012 17:55:55 -0500
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On 12/19/2012 05:35 PM, Salvatore Sanfilippo wrote:
On Wed, Dec 19, 2012 at 9:29 PM, Nick Foster<address@hidden>  wrote:
Does rtl_sdr really output 4.0Msps? I thought it was confined to 2.8Msps or
3.2Msps. If it's operating at one or the other of those two native sample
rates, you will have to resample to 4Msps for use with modes_rx, or modify
modes_rx so it resamples when using the file sink, similar to how it
resamples for rtl_sdr sources now.
Thank you for your reply Nick, yes indeed I tried different sampling
options, my last try was:

rtl_sdr -f 1090000000 -s 3200000  -g 34 modes.bin

So I set the same gain and sampling rate modes_rx uses when capturing
directly from the device.
Still after the conversion the output of modes_rx -F filename.cfile is
a lot of random meaningless mode s messages.

Maybe there is some subtle error in my conversion code even if it's so
simple that's puzzling. I'll try to write a few hand-written 8 bit IQ
samples and convert them just to see that the output is the expected
one.

The reason I'm doing this is because I want to be sure about the right
conversion from raw RTL output to cfile, as I plan to implement this
into the rtl_sdr utility itself, because many programes want cfiles as
input, so it is handy if rtl_sdr is able to output it directly.

Cheers,
Salvatore

--
Salvatore 'antirez' Sanfilippo
open source developer - VMware
http://invece.org

Beauty is more important in computing than anywhere else in technology
because software is so complicated. Beauty is the ultimate defence
against complexity.
        — David Gelernter

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The RTL *WILL NOT* support sample rates reliably above 2.4Msps, regardless of how well-appointed your CPU is. It drops them internally in
  its pipeline.  I would suggest using 2.4Msps, and up-sampling to 4Msps.


--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org





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