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

From: Salvatore Sanfilippo
Subject: Re: [Discuss-gnuradio] Problem converting RTL 8 bit IQ samples to gnuradio native format.
Date: Wed, 19 Dec 2012 23:35:56 +0100

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

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.


Salvatore 'antirez' Sanfilippo
open source developer - VMware

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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