osmocom-sdr November 2013

osmocom-sdr@lists.osmocom.org

15 participants
16 discussions

Complex FIR and Stereo support for rtl_fm
by Miroslav Slugeň 12 Nov '14

12 Nov '14

Hi again, I am working on my own SDR project for Stereo FM radio support, but i would like to also improve quality for rtl_fm application, i made unoficial patch to add: Complex FIR - to filter strong signals close to wanted signal Real FIR - to filter pilot from FM Stereo FIR Stereo Deemphasis AGC support - it can give better resolution of IQ data Some other improvments in FM radio code. All FIR filters has 3 possible variants, simple, LUT, SSE2 instricts, of course SSE is the fastest one and it should works on Intel Atoms, but not on ARM. Feel free to use any part of code in any of you programs, I know that this code is little to much to add it into rtl_fm, but maybe it could somebody help to recieve HW stereo FM radio. Speed of SSE code is much better than anything you can get around here, on Core i7 it consume only 5% of one CPU, so i could demodulate at least 80 channels at the same time in stereo quality of course. I tried this code only on AMD64 and GCC Linux, so i am not sure if it can be compiled under windows. -- Miroslav Slugeň +420 724 825 885 Teramos Multimedia s.r.o.

4 8

rtl_tcp problem or not?
by Favati 25 Feb '14

25 Feb '14

Hi there! I'm using a dongle on a raspberry + rtl_tcp and sdrsharp on another machine (quad core.... 3gb ram...good machine!) The problem occour at 00:57 http://www.youtube.com/watch?v=4E2MPfEzEi8 and at 1:34 in this video: http://www.youtube.com/watch?v=8snz1wQSRpw If i stop and start sdrsharp, it works ok for some minutes...then the problem is up again! No errors appear on the console of raspberry/rtl_tcp I'm not able to understand if it's a problem of rtl_tcp,raspberry or whatelse... Things i've tryed: 1) Changed the samplerate 2) Changed the raspberry (tested tp1/tp2 too...getting 4.98v!!!) 3) Changed the dongle 4) Updated sdrsharp The dongles tryed work ok on a pc I've no more idea.... Anyone can help me? PS: If someone know a program that works in linux and is similar to sdrsharp AND CAN INTERFACE TO A REMOTE RTL_TCP...

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odd results working at 250ksp/s
by David Jacobowitz 10 Feb '14

10 Feb '14

Hi, I've been working on a project the involves tuning VOR signals. They are narrow band signals. > 25 kHz. For that, the wide bandwidth of the RTL dongles isn't that helpful to me. (and actually a hindrance when two signals are inside the sample range but widely different strengths) Anyway, the lowest I can get my dongles (R820T) to go is 250ksps, which is fine. I've been working at that frequency for awhile, but getting some strange results. For example, if I tune in to 116.8 MHz, which should be the OAK VOR, it works fine. But if I tune to 115.8 MHz, which should be the SFO VOR I get ... the OAK VOR. That is, there is a perfect copy of the OAK signal 1 MHz shifted down. If I switch the sample rate to 1.024Msps or 900ksps, I don't get this problem. I don't understand what is happening here. 1 MHz is an even multiple of 250kHz, so maybe I'm getting an image of OAK overpowering the relatively weaker SFO signal. But should there not be filters that manage this? I guess I was expecting that if the device is set to 250ksps, then it would "close down" filters appropriately to reject signals out of that band. But maybe the filters don't work properly below a certain sample rate? Like the rtl2832 can sample down to 250ksps, but the 820T tuner was not designed for it? Or perhaps I'm doing something wrong? Can I control the filters directly? I'm glad I find this issue because I was going nuts thinking my software had some mysterious bug. But I can reproduce this issue just with SDR# or whatever. :-) Regards. Dave J

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How to get IQ samples from multiple rtl-sdr dongles in a synchronized manner?
by Jiao Xianjun 02 Jan '14

02 Jan '14

Hi, I want to use multiple rtl-sdr dongles to do some multi-antenna experiments. Is it possible to read IQ samples from multiple rtl-sdr dongles in a synchronized manner? I already have a glance at dump1090 codes, which is a project using rtl-sdr to decode aircraft broadcasting ADS-B messages in 1090MHz. Seems that I should use rtlsdr_read_async() instead of rtlsdr_read_sync(), because that if rtlsdr_read_sync() is used, I have to call it multiple times sequentially. That looks not synchronized. But rtlsdr_read_async() function only accept one rtl-sdr device as input parameter, and it will be blocked after it is called. So seems that it also can't be used for my purpose directly. Also welcome any opinion on how to improve rtl-sdr lib/driver to support this feature. Thank you. BR Jiao Xianjun

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OsmoDevCon 2014 / Date / Venue
by Harald Welte 01 Jan '14

01 Jan '14

Hi all, time is moving fast, and I want to start some initial discussion and planning for OsmoDevCon 2014. There are basically four questions which I'm raising below. Please provide your feedback to the osmocom-event-orga mailing list only, to avoid cross-posting over all the project lists. = Who? = My intention is to keep it an 'active developer/contributer only' event, like we had it before. I would also want to keep the group relatively small, to keep the 'Osmocom family' atmosphere. If desired, we could have one half or full day of public prsentations in a larger auditorium, but the developer meeting should be a close group, as known so far. = Where? = If we keep the number of attendees within the same range as this year, then I'm sure we could again hold it at the same venue. I know it is not perfect, but it is a place that we have access to, 24 hours per day, and free of cost for community projects like osmocom.org. If the community wants a larger event, then this is something that would require more funds and much more time organizing. And that is something that I personally could not offer to take care of, sorry. I'm happy to attend and support any larger events, but I'm unable to take care of fundraising and venue research. = When? = Q1/2014. In January, I'm not aware of any 'blocker' events. February, there is Fosdem (Feb 1 + Feb 2), and MWC from Feb 24 through Feb 27. In March there is CeBIT (March 10-14) and Easter holidays (with EasterHegg March 17-21). Did I miss any other FOSS / mobile event that might clash in Q1? So my preference woudl be to do it either late January (23-26) or in February (6-9 or 13-16). Any preferences regarding preferred schedule? Once we have some concencus here on the list [and we want to do it in the same size / venue], I'll talk to IN-Berlin. = What? = I think that question is easy to answer, if we have the above three figured out... There's no shortage of topics, I suppose. You can start adding your suggestions to http://openbsc.osmocom.org/trac/wiki/OsmoDevCon2014 Regards, Harald -- - Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/ ============================================================================ "Privacy in residential applications is a desirable marketing option." (ETSI EN 300 175-7 Ch. A6)

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PL/CTCSS/DCS squelch on rtl_fm?
by Chris Hanson 09 Dec '13

09 Dec '13

Has anyone considered adding this or found a work around for those noisy stations that keep breaking the squelch? Thanks Chris

4 4

E4000 tuner gain settings
by Jochen Arndt 27 Nov '13

27 Nov '13

During implementation of signal strength calculations I came across some problems with E4000 tuners. The RTLSRD library uses these E4000 gains: const int e4k_gains[] = { -10, 15, 40, 65, 90, 115, 140, 165, 190, 215, 240, 290, 340, 420 }; These are the gains from Table 6 of the data sheet plus the mixer gain of 12 db for the last value and 4 db for all others. But the last gain of 30 db from Table 6 is only valid when LNA gain enhancement is enabled. Cite from datasheet section 1.16 LNA Gain enhancement: "The LNA gain numbers quoted throughout this document assume that this register is programmed to the recommended value." The RTLSDR libary actually does not change the LNA gain enhancement register AGC11 with manual gain mode and clears it with automatic gain mode. So the last two values of the e4k_gains array must be: 290 = 250 + 40 (max. LNA gain + low mixer gain) 370 = 250 + 120 (max. LNA gain + high mixer gain) With enabled LNA enhancement, the last value would be 420 = 250 + 120 + 50 (max. LNA gain + high mixer gain + enhancement) However, enabling LNA gain enhancement did not work (like the larger LNA gain step size of 5 db). I have verified the above by measuring pure carrier signals of different strength using FFT and subtracting the total gain. Using the corrected values, the changings in the measured signals correspond to the changings of the transmitted signal. With automatic control, the values has been also compared with the input power calculated from the RSSI indicator and LNA gain. The second to last value of Table 6 is also 25 db. I assume that this is a misprinting and the correct value is 22.5 db. Then the corresponding e4k_gains array entry must be changed from 290 to 265. Mixer Gain (automatic mode) In automatic mode, the mixer control register AGC7 is set to 0x01. This will enable autonomous control with a threshold value of zero resulting in always using the high mixer gain of 12 db. When the received signal is inside the automatic gain range (> -50 dbm), the output voltage of the LNA is so high that applying any amplifying afterwards usually results in overdrive samples. Therefore, the automatic mixer gain should be disabled or set to switch to high mixer gain at max. LNA gain by setting control register AGC7 to 0x1D. For the same reason, the total IF gain should be set to less than 10 db. Applications using automatic gain control can then increase the IF gain when the input signal is below -50 dbm to extend the sensitivity range. NOTE: Section 1.15.2 of the datasheet states that writing 0x15 to AGC7 corresponds to a LNA gain threshold of 7.5 db. This is obviously wrong (verified by reading the mixer Gain2 register with different signals). I hope this is helpful Jochen Arndt

1 0

MiricsFlexiTV-MSI3101
by marzano 21 Nov '13

21 Nov '13

A quite good (AM/SW)/FM/DAB/DVB-T USB dongle. Mirics FlexiTV MSi3101 (two chips MSi001+MSi2500) http://www.mirics.com http://www.mirics.com/node/31 Data sheets available, register yourself at Mirics portal. RF Tuner: MSi001/MSi002 ( used by FUNcubrePro+ ?), seems better than R820T ADC and HiSpeed USB interface: MSi2500 . ADC 10 bit , better than 8 bit RTL2832U aDC. Windows binary software available: FMDABplayer, DVB_T decoder, Windows lib.dll and API doc. IO-DATA GV-TV100 stick sold on Japan . Stick, chips and dev board available from Mirics. Linux software at address http://cgit.osmocom.org/libmirisdr/ It seems project on stand-by . Can author Steve Markgraf comment ? Francesco

3 2

multiple devices in one process?
by Michel Pelletier 14 Nov '13

14 Nov '13

I've been thought-experimenting with capturing data from two devices and measuring their correlation. For example, if two rtl-sdr processes are launched to read one sample block from two devices, how closely do the two devices' samples line up with each other in time? I'm expecting that there will be no reliable correlation. My working theory is that each process calls into libusb_handle_events_timeout according to its own process schedule and that there is no way to coordinate these two calls to happen closely enough in time for the transfers to happen in a more synchronized fashion. Threads do not appear to be any better solution to the problem. I'm not an expert in usb transfers, or libusb, or rtlsdr for that matter, so I'm going only on what I can glean from reading the source code of librtlsdr.c and libusb documentation. libusb does say however that it can specifically handle multiple devices in one async loop. Multiple bulk transfers can be set up to multiple devices in one process, and one call to libusb_handle_events_* can be used to handle those transfers. My thinking is that because the triggering event for both samples is now the same function call in the same process, the samples will be more synchronized, ideally down to some reliably offset of say a few microseconds. Juha Vierinen's hard-hack to make two devices use a coherent sample clock makes this idea even more interesting to me. But, it doesn't look like librtlsdr can handle multiple devices. I'm game to take a stab at a patch that can extend its functionality. But I wanted to run this idea by the community first before spending code time on figuring this out. Do the experts here think that there is any potential benefit to be gained by taking this approach? -Michel

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Re: rtl_fm and r820t tuner
by Miguel A. Vallejo 14 Nov '13

14 Nov '13

*>>>Please humor me. How are you determining that the gain is not being set?* See my previous message with Baudline captures: ~$ rtl_fm -f 89000000 -R -s 1000000 -g 0 - | baudline -stdin -samplerate 1000000 -quadrature -flipcomplex -channels 2 -format le16 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: 2x. Oversampling output by: 1x. Buffer size: 4.10ms Tuned to 89500000 Hz. Sampling at 2000000 Hz. Output at 1000000 Hz. Exact sample rate is: 2000000.052982 Hz Tuner gain set to 0.00 dB. Result: https://dl.dropboxusercontent.com/u/102802145/baudline0dB.jpg ~$ rtl_fm -f 89000000 -R -s 1000000 -g 30 - | baudline -stdin -samplerate 1000000 -quadrature -flipcomplex -channels 2 -format le16 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: 2x. Oversampling output by: 1x. Buffer size: 4.10ms Tuned to 89500000 Hz. Sampling at 2000000 Hz. Output at 1000000 Hz. Exact sample rate is: 2000000.052982 Hz Tuner gain set to 29.70 dB. Result: https://dl.dropboxusercontent.com/u/102802145/baudline30dB.jpg GQRX, LNA gain = 0dB Result: https://dl.dropboxusercontent.com/u/102802145/gqrx0dB.jpg GQRX, LNA gain=30dB Result: https://dl.dropboxusercontent.com/u/102802145/gqrx30dB.jpg I know its very strange but I lost two days trying to make work a project here before I realized rtl_fm was outputting only noise.

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osmocom-sdr November 2013