osmocom-sdr

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916 discussions

Filtering in baseband spectrum
by Neela Neela 08 Aug '13

08 Aug '13

Hi I am a beginner with RTL and observing that the baseband spectrum is centred at 0 Hz and is asymmetric going from -1 MHz to +1 MHz. How does one filter a part of such a spectrum? For example if signal of interest lied in -300 kHz to -150 kHz. The filtering techniques for typical band pass filters work with positive frequencies and have symmetric frequency selection response. As such a 150 to 300 KHz band pass filter will select signal in both 150 to 300 kHz band as well as from -150 to 300 kHz. Is there a special filtering method available to work with negative frequencies and with an asymmetric baseband spectrum. I am sure this has been addressed as preassumably the FM and other signals of interest are filtered somehow. Any indications will be appreciated. Regards

2 1

IQ Balance
by Richard Ranson 07 Aug '13

07 Aug '13

I am new to this group and would appreciate any help. Looking at the rtlsdr driver, I see that there seems to be some code to correct the IQ balance, but I'm only going by the names of functions like "_IQ_Tree" and "_Compare_Cor". The algorithm, if there is one, is not at all clear nor of direct interest, the question is whether or not there is some IQ balance built into the rtlsdr driver and does anyone know how effective (e.g. in terms of image suppression) it is. Then, I'm using this device and software to demonstrate to students the concepts of SDR. So on a related note, if there is some IQ balance correction in the driver, can it be turned off? Changing the driver code is way beyond my ability, but some digging suggests that changing the header file to have #define IMR_TRIAL 0. eliminates a quite complex looking loop of computation that may be the IQ balance scheme. As a newbie I wouldn't attempt this without some positive guidance. It would require a new build of the driver, which I imagine is the same as for the normal case, and then if it can be done, it would be great to illustrate the basic IQ balance of the hardware and the improvement possible with software correction. thanks Richard

2 1

openLTE release V00.08.03
by Ben Wojtowicz 04 Aug '13

04 Aug '13

All, I have released openLTE V00.08.03 (http://sourceforge.net/projects/openlte/) with support for HackRF and RTL-SDR via GrOsmoSDR. Using this release, I have been able to successfully decode broadcast information (MIB and SIBs) from LTE networks. I was also wondering if there is a good way to determine which type of hardware is connected? Currently I am using the get_sample_rates routine and comparing the maximum against the expected max for each hardware type. Thanks, Ben

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RTL SDR Hardware Architecture
by Lucas Ingles 01 Aug '13

01 Aug '13

Hello to all, I am an electrical engineering student from Brazil and I have already been studying GNURadio using RTL-SDR for a while (I have an EZCAP dongle). This is my first post here. I am studying the basic FM receiver and my question is: Which is the actual receiver architecture used in the RTL-SDR dongles? I mean, do we have a Hartley receiver, a Weaver receiver, a zero-IF receiver, a low-IF receiver? Also, the E4K tuner has two outputs: one output is the in-phase component and the other output is the quadrature component. So, does the RTL2832U has two ADCs to sample the two components? Or just one ADC and it samples the two components interleaved? Thanks very much in advance, Lucas Ingles

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ACARS decoder using rtl-sdr
by Skip Tavakkolian 29 Jul '13

29 Jul '13

Hi, Thank you Thierry and Andreas for your work. I've been experimenting with rtl-sdr library with different RTL2832U devices -- initially for receiving/decoding ADS-B data, and now for ACARS data -- and have been very impressed by the device and the code. For ACARS I was on the same path -- i.e. merging Thierry's code with rtl_fm (AM mode) -- and I'm very happy to see Andreas has already done it! Incidentally, my plan for writing an ADS-B decoder was also (fortunately) shortened when I discovered Dump1090 (Salvatore Sanfilippo) and a nice fork of it (MalcolmRobb). To compile rtl_acars.c, I added it to my local rtl_sdr source directory and made a few mods to the CMakeLists.txt files, etc to build/install it. The diffs can be found here (includes my mods to CMakeLists.txt to compile on Mac OS X): http://pastebin.com/nwjtUDqC -Skip Thierry Leconte wrote: > Le 15/07/2013 09:54, Andreas Reinhardt a écrit : > > Hi everyone, > > > > I have combined "rtl_fm" with Thierry Leconte's (GPL'ed) acarsdec > library code and created "rtl_acars" which can directly decode ACARS flight > info messages to the console. > Hey that's great news! > I just bought a rtl card for fun recently and subscribe to this list . > Very happy to see someone use my very old acars decoder code :-) > will try it very soon !

2 1

RTL_FM raw mode squelch
by Sdr Guru 29 Jul '13

29 Jul '13

Hi Please enable raw mode squelch. It does wonders when debuging remote loctions (ppm_error!). And significantly reduces data volumes. rtl_fm -R -f 1**M -s 12k -l 220 | sox -r 12k -t raw -e signed-integer -b 16 -c 2 -V1 - -C 0 out.flac sox out.flac out_s.wav silence -l 1 0.2 1% -1 2.0 1% SG

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Re: osmocom-sdr Digest, Vol 20, Issue 12
by Peter Stuge 29 Jul '13

29 Jul '13

Peter Dohm wrote: > I can show you screen shots of zadig if you'd like to see them, Even if they look good that's actually not good enough.

1 0

Terratec T-Stick+ oddity in Windows 8
by Peter Dohm 29 Jul '13

29 Jul '13

Hi. As it appears, the Terratec T-Stick+ is supported properly in the latest releases of osmocom's libraries. I have a T-Stick+ working properly in SDRSharp using the latest version of the standard zadig drivers as everyone on Windows uses. When i downloaded the latest osmocom Windows binaries from here: http://sdr.osmocom.org/trac/attachment/wiki/rtl-sdr/RelWithDebInfo.zip, i get the following result when i run rtl_test.exe on a fully-patched Windows 8 64-bit OS: C:\Users\user\Downloads\RelWithDebInfo\rtl-sdr-release\x64>rtl_test.exe -t Found 2 device(s): 0: Terratec T Stick PLUS 1: Terratec T Stick PLUS Using device 0: Terratec T Stick PLUS usb_open error -12 Failed to open rtlsdr device #0. I've tried this both as administrator and as a normal user, btw. Curiously enough, HDSDR also can not locate the device for some reason no matter what I do, and i've installed the zadig drivers on BOTH tuner instances just to be sure... Somewhat perplexed... Can anyone offer any advice? Cheers Peter Dohm

2 1

ACARS decoder using rtl-sdr
by Andreas Reinhardt 21 Jul '13

21 Jul '13

Hi everyone, I have combined "rtl_fm" with Thierry Leconte's (GPL'ed) acarsdec library code and created "rtl_acars" which can directly decode ACARS flight info messages to the console. Confirmed to compile on OSX 10.6 (not possible for me to check if it also compiles under Windows and *nix). Feel free to add it as another proof of concept to your distro unless you consider it too much of a quick&dirty hack. Grab the code from: http://pastebin.com/kLJHyQWt Best regards, Andreas

4 4

Re: ACARS decoder using rtl-sdr
by Pawel Janowski 19 Jul '13

19 Jul '13

Hello its great idea ! I think the next step (small for man big form mankind) should be decoding (based on rtl_fm) APRS messages and putting into APRS-IS Servers ! with regards Pawel, SQ7MRU http://sq7mru.blogspot.com/

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