- osmocom-sdr - lists.osmocom.org

How RTL-SDR samples signals
by Lucas Ingles 20 Aug '13

20 Aug '13

Hello to all, Please, can someone help me to understand how RTL2832U samples signals? I know it has two ADCs, one for the I (in-phase) component and other ADC for the Q (quadrature) component. In http://superkuh.com/rtlsdr.html the author states the signal is sampled initially at 28.8 Msps and then re sampled to present whatever sample rate is desired. But http://www.realtek.com.tw/products/productsView.aspx?Langid=1&PFid=35&Level… says that 28.8MHz is the frequency of the crystal, not the ADC. I am confused with that, can someone help me? If RTL2832U is able to sample at 28.8Msps, why don't use the maximum sample rate? Maybe USB limitations? Also, all ADCs used in RTL-SDR dongles are inside RTL2832U? Or we have external ADCs? Thanks very much in advance, Lucas Ingles

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Is My RTL2838U + R820T Tuner working?
by Curt Carpenter 20 Aug '13

20 Aug '13

Hello! I received my USB-DVB-T+DAB+FM dongle last week, and have been trying to find a signal with it since, but with no luck. Can anyone tell me how to tell if it is working at all? I'm using the Windows version of Osmocom under WinXP. Using rtl_eeprom, I get the following display: -------------------------- Vendor ID 0x0bda Product ID 0x2838 Manufacturer Realtek Product RTL2838UHIDIR Serial Number 00000000001 Serial Number Enabled Yes IR Endpoint Enabled Yes Remote Wakeup Enabled No ----------------------- When I run rtl_test -s 1.6e6 I get the following response: ----------------------- Found 1 device(s) 0: ezcap USB 2.0 DVB-T/DAB/FM dongle Using device 0: ezcap USB 2.0 DVB-T/DAB/FM dongle Supported gain values(29): 0.0 0.9 .... 49.6 Info: This tool will continuously read from the device, and report if samples get lost. If you observer no further output, everything is fine. Reading samples in async mode... -------------------------- If at that point after a while I press Control C, I get --------------------------- Signal caught, exiting! --------------------------- But then my command prompt window hangs up and will do nothing until I close it all together. Does it appear that my dongle is working? Where do I find out how to use the different gains that are listed by rtl_test? Could my difficulties have anything to do with the fact that my dongle is IR Endpoint enabled? I am brand new to this, and haven't had much luck so far, although I think I've gotten further with Osmocom and Windows than with anything else I've tried. Any help/advice/links to more information will be much appreciated. Sorry for the long post -- I was trying to provide as much information as I could. Thanks Curt Carpenter

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OpenBSD: crashing
by Alan Corey 18 Aug '13

18 Aug '13

This is with a version of rtl-sdr I got by git last night and OpenBSD 5.2 (current release). 5.2 has some pthreads fixing so I waited until I bought another computer and loaded it. Are the crashes related to threads? I don't know, but possibly. It didn't work with OpenBSD 5.0 either. rtl_fm crashes and uses threads rtl_adsb crashes and uses threads rtl_tcp doesn't crash, uses threads, actually stops on ctrl-c rtl_test doesn't crash, doesn't use threads, won't stop rtl_eeprom doesn't crash, doesn't use threads, ends normally I'm not real practiced using gdb but I tried looking at a couple of core files, here's a run of rtl_fm: rtl_fm -f 162550000 -N - | play -t raw -r 24k -e signed-integer -b 16 -c 1 -V1 - -: (raw) Encoding: Signed PCM Channels: 1 @ 16-bit Samplerate: 24000Hz Replaygain: off Duration: unknown In:0.00% 00:00:00.00 [00:00:00.00] Out:0 [ | ] Clip:0 Found 1 device(s): 0: Realtek, RTL2838UHIDIR, SN: 00000013 Using device 0: ezcap USB 2.0 DVB-T/DAB/FM dongle Found Rafael Micro R820T tuner Oversampling input by: 42x. Oversampling output by: 1x. Buffer size: 8.13ms Tuned to 162802000 Hz. Sampling at 1008000 Hz. Output at 24000 Hz. Exact sample rate is: 1008000.009613 Hz Tuner gain set to automatic. In:0.00% 00:00:00.00 [00:00:00.00] Out:0 [ | ] Clip:0 Done. Abort (core dumped) d530# gdb -c rtl_fm.core /usr/local/bin/rtl_fm GNU gdb 6.3 Copyright 2004 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "i386-unknown-openbsd5.2"... Core was generated by `rtl_fm'. Program terminated with signal 6, Aborted. Reading symbols from /usr/lib/libpthread.so.16.0...done. Loaded symbols for /usr/lib/libpthread.so.16.0 Reading symbols from /usr/lib/libm.so.7.0...done. Loaded symbols for /usr/lib/libm.so.7.0 Reading symbols from /usr/local/lib/librtlsdr.so.0.0...done. Loaded symbols for /usr/local/lib/librtlsdr.so.0.0 Reading symbols from /usr/local/lib/libusb-1.0.so.1.0...done. Loaded symbols for /usr/local/lib/libusb-1.0.so.1.0 Symbols already loaded for /usr/lib/libpthread.so.16.0 Reading symbols from /usr/lib/libc.so.65.0...done. Loaded symbols for /usr/lib/libc.so.65.0 Loaded symbols for /usr/libexec/ld.so #0 0x0abbd98d in kill () from /usr/lib/libc.so.65.0 (gdb) bt #0 0x0abbd98d in kill () from /usr/lib/libc.so.65.0 #1 0x0ac29545 in abort () at /usr/src/lib/libc/stdlib/abort.c:68 #2 0x005e9298 in pthread_mutex_unlock (mutexp=0x3c003d8c) at /usr/src/lib/librthread/rthread_sync.c:218 #3 0x1c00266e in full_demod (fm=0xcfa2de5c) at /usr/src/misc/osmocom/2013-04-15/rtl-sdr/src/rtl_fm.c:583 #4 0x1c0028ff in demod_thread_fn (arg=0xcfa2de5c) at /usr/src/misc/osmocom/2013-04-15/rtl-sdr/src/rtl_fm.c:641 #5 0x005ebc2e in _rthread_start (v=0x84da4c00) at /usr/src/lib/librthread/rthread.c:111 #6 0x0aba62e9 in __tfork_thread () from /usr/lib/libc.so.65.0 The backtrace (bt) shows that it dies trying to do a mutex_unlock (I think). rtl_tcp also does a mutex_unlock and it doesn't crash. I'm probably reading it wrong for all I know. I don't know what's causing the signal 6 either. I'd also like to get the -lrt of of the cmake files. OpenBSD doesn't use or have lrt, it works without. I can edit it out and compile, but every time I run cmake again, I have to edit the files again. Alan ----- Radio Astronomy - the ultimate DX

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Fwd: Need a starting point to learn RTL-SDR
by Andrew Mount 11 Aug '13

11 Aug '13

---------- Forwarded message ---------- From: *Andrew Mount* Date: Friday, August 9, 2013 Subject: Need a starting point to learn RTL-SDR To: Andrew Back <andrew(a)carrierdetect.com>, " osmocom-sdr-request(a)lists.osmocom.org" < osmocom-sdr-request(a)lists.osmocom.org> Andrew, Thank you. I have two radio astronomy projects in mind. The first is a HF system that will enable me to pick or zoom into a narrow band of frequencies , say 20-22 mHZ from a larger 18 - 26 mHZ range ( currently scanned by a spectrograph) to study N type storm events from Jupiter. This will require coding on my part as I have to interface with pre-existing software in order to load data accepted by the NASA RADIO JOVE archive. The other application ( much easier) is to build an RTL based 220 mHZ range meteor scatter detection system. The meteor detection system is the current project. I have the computer, the RTL and am waiting on the antenna, ( due to arrive by 30 August). This has already been worked out software wise, it is a plug and chug type of project. The advantage is that I can be collecting meteor data by the end of the year and I will learn about RTL SDR in the process. In order to build my own custom SDR system, what is needed is knowledge of a more how to -and what is- type. I need to learn the technical language, what programs to use, how an RTL works, integration with a build ( i have access to Matlab? ) environment, how to write drivers, etc. I need to know how it works, how to speak the language and what are the prerequisite tools to get the job done. Any suggestions that would build proficiency in these areas would be invaluable for me. Thanks for responding so quickly and best wishes, Andy On Friday, August 9, 2013, Andrew Back wrote: > On 9 August 2013 13:03, Andrew Mount <capeorion(a)gmail.com> wrote: > > Are there any good books or Internet references that the listserv members > > could recommend as a starting point ? > > > > I am an amateur astronomer who is interested in learning how to use > RTL-SDR > > to do radio astronomy. > > The top Google result looks promising: > > http://www.rtl-sdr.com/rtl-sdr-for-budget-radio-astronomy/ > > Regards, > > Andrew > > -- > Andrew Back > http://carrierdetect.com >

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Need a starting point to learn RTL-SDR
by Andrew Mount 09 Aug '13

09 Aug '13

Are there any good books or Internet references that the listserv members could recommend as a starting point ? I am an amateur astronomer who is interested in learning how to use RTL-SDR to do radio astronomy. Thank you, Andy Mount

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Filtering in baseband spectrum
by Neela Neela 09 Aug '13

09 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

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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

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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 02 Aug '13

02 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 !

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