osmocom-sdr

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912 discussions

[PATCH] rtl_adsb: Fix invalid memory access
by Will Glynn 13 Sep '13

13 Sep '13

single_manchester() considers both i and i+1, but the loop only tests that i is in bounds. This causes undefined behavior, including but not limited to a SIGBUS-related crash on Mac OS X. --- src/rtl_adsb.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/src/rtl_adsb.c b/src/rtl_adsb.c index 44b62e2..3c353a0 100644 --- a/src/rtl_adsb.c +++ b/src/rtl_adsb.c @@ -258,6 +258,7 @@ void manchester(uint16_t *buf, int len) uint16_t a=0, b=0; uint16_t bit; int i, i2, start, errors; + int maximum_i = len - 1; // len-1 since we look at i and i+1 // todo, allow wrap across buffers i = 0; while (i < len) { @@ -275,7 +276,7 @@ void manchester(uint16_t *buf, int len) i2 = start = i; errors = 0; /* mark bits until encoding breaks */ - for ( ; i < len; i+=2, i2++) { + for ( ; i < maximum_i; i+=2, i2++) { bit = single_manchester(a, b, buf[i], buf[i+1]); a = buf[i]; b = buf[i+1]; -- 1.8.3.4

2 2

R820T vs. E4000
by Benedikt Heinz 09 Sep '13

09 Sep '13

Hi everyone, although there are some comparisons between the R820T and the E4000 already [1, 2], I also did some tests with another use-case in mind. I'm working on a thing similar to RTLSDR-Scanner [3]. I want to monitor a large part of the spectrum continuously. So I compared the R820T with the E4000 using RTLSDR-Scanner w/ and w/o an antenna. My results are here: https://docs.google.com/folder/d/0ByDAKwyEiyx_XzZ5ZnpRV1VZWDQ/edit?usp=shar… There's much more spurs with the E4000 than w/ the R820T. According to [1, 2] one also would expect a better overall sensivity compared to the E4000. However, the GSM900 signals for example seem to be way better with the E4000 according to the RTLSDR-Scanner. Tuning to a certain channel w/ OsmoSDR Source in GNUradio gives about the same SNR - contrary to the RTLSDR-Scanner output. Can anyone explain this? Also, the DVB-T channel at 502MHz is quite weak in the R820T RTLSDR-Scanner output when compared to the E4000. I had a closer look at the lower limit of the channel in gnuradio. This can be seen in the 502MHz_*.png pictures. The E4000 produces a nice +20dB step while one can hardly see the channel in the R820T spectrum. I don't understand this as well. Is this AGC-related? Manually setting a fixed gain didn't really help though... Any explanations? Thank you! Best regards, Hunz [1] http://steve-m.de/projects/rtl-sdr/tuner_comparison/ [2] http://www.hamradioscience.com/rtl2832u-r820t-vs-rtl2832u-e4000/#more-1852 [3] https://github.com/EarToEarOak/RTLSDR-Scanner

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rtl-sdr on Nokia n900 phones
by Anonymous 08 Sep '13

08 Sep '13

I heard someone recently made rtl-sdr work on an n900. Is it just working drivers, or is it actually usable? I ask, because the processor may not be up to the job.

1 0

Reset after hot insertion of USB tuner
by Richard Ranson 02 Sep '13

02 Sep '13

I have had great help before from this list, so many thanks for that. I am using an ezcap tuner with a raspberry pi running a Debian based linux OS called Raspbian. I have built the drivers from the git hub and they work fine. As an aside, I found the installation much easier than when I tried it directly on my PC. My question is that I find that if I plug the USB device in when linux is running, it causes a re-boot of the whole OS. (btw, disconnection has no effect). Is this the case with full blown linux systems, or just some peculiarity of the more limited raspberry pi? Also, it is a bit of a nuisance, so does anyone know of a way to stop this? many thanks Richard

2 1

Calibration / PPM
by John 30 Aug '13

30 Aug '13

I am trying to get my head around calibration of my RTL dongle. I used gqrx with a known frequency (467.6375Mhz). Based on this, the dongle needs offset of -16Khz. In gqrx, this offset can be entered directly in the user interface. With rtl_test -p, the PPM number varies. I have gotten positive and negative numbers. When using the RTL block in gnuradio companion, I need to enter PPM. I have seen various formulas to calculate PPM from frequencies but for me they do not yield sane results. I could be just misusing these formulas. Any assistance would be appreciated. Thanks, John

1 1

Re: About 'internal AGC'
by Leif Asbrink 28 Aug '13

28 Aug '13

Hi Charlie, The controls for AGC do not affect the peculiar wideband LNA AGC in the R820T chip. The RTL1090 uses the same rtlsdr.dll as is used by SDR#. I do not know how to evaluate noise levels and signal levels in RTL1090, but with SDR# one can see funny things directly on the waterfall. The LNA is followed by a VERY sensitive power detector that is somehow followed by filters and amplifiers. It is arranged in a way to not react on narrowband signals, but already a 3 dB increase of the noise floor causes a loss of gain through AGC action. Most striking is this experiment: Connect a combiner to the input of the dongle and use it to combine a signal generator and a noise source. The noise source needs a filter that assures that it does not add any noise on the frequency of the desired signal. It is OK to use a T-connector if you do not have a wideband combiner. I used a 100 MHz low pass filter connected to a vacuum diode noise source cabable of delivering 17 dB excess noise combined with a signal generator on 144 MHz by use of a T connector. I used SDR# to look at the spectrum around 144 MHz. Without "RTL AGC" and without "Tuner AGC" the noise floor does not change when the noise source is switched on or off. That is expected because the noise source can not send any noise through the 100 MHz low pass filter. That is true at modest gain settings, but if the gain is set at maximum (49.6 dB) the noise floor increases by 3 dB when the noise source is turned on. A small but unexpected effect. The signal however is attenuated by 23 dB for a total loss at max gain of S/N of 26 dB!!!!! Please note that the true S/N is not affected at all. There is no noise added at 144 MHz. If I switch on "RTL AGC" or "Tuner AGC" or both, S/N still changes the same way. Depending on the signal level of the 144 MHz signal one can see the signal go down or the noise go up. Or both. The way sensitivity is lost due to out-of-band noise is invisible to the user. There is no warning about overload. The noise power from 0 to 100 MHz is -174+17+80 = -77 dBm ( -174 dBm/Hz = room temp) ( +17 dB is excess noise) ( +80dB is 100/MHz/1Hz) There is some filter loss and the dongle presumably has a high pass filter so one can assume that the noise power is -80 dBm RMS. I have tried to activate the LNA AGC by use of narrowband signals in the 50 to 100 MHz range. Even two signals at -30 dBm each do not have any effect regardless of the frequency spacing. It seems the "intelligent" power detector of the LNA AGC can reject narrowband signals even if they are much stronger than the noise floor. The wideband LNA AGC in the R820T may cause problems when an up-converter is used in front of the dongle. The noise floor of the up-converted HF spectrum may cause unexpected loss of sensitivity in the upper part of the HF spectrum where the noise floor is low. Adding a filter for the desired HF band. With some gain to ensure that the noise floor is higher in the desired frequency range than elsewhere could perhaps make the R820T dongles behave much better. 73 Leif / SM5BSZ > I use a R820T chipped dongle for receiving aircraft transponder signals > through a specialised application called RTL1090 from jetvision, the control > panel of which allows the tuner and device AGCs to be independently toggled > on or off. I have not however used this with SDR-Radio in the past so cannot > comment on the optimum settings. > > > > 73 > > Charlie > > www.G4EST.me.uk > > > > From: sdr-radio-com(a)yahoogroups.com [mailto:sdr-radio-com@yahoogroups.com] > On Behalf Of Leif Asbrink > Sent: 10 August 2013 22:30 > To: sdr-radio-com(a)yahoogroups.com > Subject: [sdr-radio-com] Re: About 'internal AGC' > > > > > > Hello Patrick and All, > > The R820T chip has an advanced AGC function that I do not > think can be disabled. The chip detects the noise floor > in a wide bandwidth and adjusts the gain to keep the noise floor > constant. > > The wideband AGC has surprising effects. If one tries to measure > the noise figure with a noise source that is manually switched > on and off one finds a really bad NF. That result is false however, > if one measures S/N of a weak signal one finds the true NF which > is quite good. > > To verify the finding one can inject a weak signal together > with the signal from a noise source. What happens when the > noise is turned on is that the signal becomes weaker while > the noise floor does not change. > > A 500 kHz wide filter in front of the R820T chip converts the > noise from the noise source to a narrowband signal which will > not affect the wideband AGC. > > I made some effort to switch this feature off but failed. > > The behaviour is probably quite clever for reception of digital TV > but I find it very disturbing in a general purpose SDR. I did not > take notes and I did not investigate in detail what types of signals > will affect the AGC and what types will not. That would be > a big investigation and I see no reason to do it because there > are other chips. > > The R820T gives good signals many times but I do not like the feeling > of not knowing what I am doing..... > > The "internal AGC" option is another thing as far as I understand. > The chip has RF AGC as well as IF AGC. > > 73 > > Leif / SM5BSZ > > > Hello Group, > > > > When using a DVB-T type dongle (mine is a R820T), do you tick the > "internal AGC" option or not ? > > > > I tried both "internal AGC" desactivated (with more gain) and AGC > activated (less gain to avoid spurs from my local FM TX) ... I can't tell > which one is better. Even on weakish sigs it's about the same. > > > > What about your experience ? > > > > Regards, > > Patrick > > > > >

3 8

Debian Jessie and kernel 3.9.1
by Anton Komarov 24 Aug '13

24 Aug '13

Tested several rtl dongles with linux 3.9.1 on Debian Jessie (testing) and got disappointing results 2 dongles simultaneously working ok if using 3 or more than 3rd dongle not working (1st and 2nd working ok) in Debian Wheezy i did manage to run 5 dongles simultaneously (kernel 3.2) i suppose developers should pay attention to than fact. -- public PGP key http://pastebin.com/dqZqgyVE

4 3

Proposal: Java wrapping of .dll/.so
by Alessandro Staniscia 20 Aug '13

20 Aug '13

Hi ml users, I'm a newbie of this ml and this is my first message. So, just a little presentation of me: I'm a Software analyst and I work full time with java and some time in C++. I was a linux user on my beautiful but defunct linux laptop! Now (almost 15 days) I'm a linux user on windows laptop. Into the company, java is a solution to write a Crossplatform service and software. In my free time I have used various tools based of rtlsdr library, and I found very difficult to retrieve alternative of all linux-based software! So, if I would write java program, does exist a java wrapping of rtlsdr library? In your opinion, building a wrapper of the library is a stupid or a good feature? IMHO many software ( parser/plotter/networktool) are written in java and this is a opportunity for the library to retrieve this knowhow. What do you think?

1 0

Problems compiling rtl-sdr on debian
by lee jones 20 Aug '13

20 Aug '13

Hello all! Just been trying to compile rtl-sdr ( http://sdr.osmocom.org/trac/wiki/rtl-sdr ) on my linux box but I'm having a few problems. Btw the linux distro is debian running a 64-bit kernel; 3.10-1-amd64. Here's the problem. I can't seem to get rtl-sdr to compile quite right either with the cmake or autotools instructions from the sdr website. I've tried both methods; only one completes (but produces an unstable version) the other version dosen't compile at all. Here's the output I get from trying to build by using cmake - http://slothpuck.no-ip.org/tmp/cmake-build.txt and then with autotools method - http://slothpuck.no-ip.org/tmp/autoconf-build.txt I get a lot of errors with the cmake method with lots of warnings about unused paramaters; the autotools method dosen't even complete. The cmake version does however but appears to be very unstable. If I try to run one of the programs made by rtl-sdr -- the program rtl_tcp with another program such as gqrx, .e.g by starting rtl_tcp in a terminal then run gqrx in another ( http://www.oz9aec.net/index.php/gnu-radio/gqrx-sdr ) I find it causes rtl_tcp to crash - either with a segfault, or with a "worker cond timeout, signal caught exiting!" message (rtl_tcp hung in this case). I do have libusb (both library and dev) and gnuradio installed btw. any thoughts on what might be going wrong at all? Thanks ljones

4 11

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

20 Aug '13

Just to close the loop... Thanks to Skip's link to rtl_fm here on the list, I've finally managed to get my dongle working, and am happily listening to my local FM station on my computer now :-) And now that I'm sure my hardware is working, I can start to explore the osmocom software seriously. Thanks for the help!

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