osmocom-sdr September 2013

osmocom-sdr@lists.osmocom.org

31 participants
17 discussions

[PATCH] rtl_sdr: Direct sampling mode + RTL AGC
by psb hlw 16 Sep '13

16 Sep '13

Hi, I didn't find rtl_sdr with implemented direct sampling mode, so I made the patch. Also it has an option to set RTL AGC on. This feature allows to use tuners as cheap data loggers without changing the schematic of the tuners. You can just connect wires directly to pins 1-2 of RTL2832 (I channel, diff. input) or pins 3-4 (Q channel, diff. input). When direct sampling mode is on - tuner's chip outputs are disabled and doesn't affect external signal. For example, this command will write 8 bit samples to file 'mydata' at 2.4 MHz sampling rate with automatic gain: rtl_sdr.exe -f 0 -s 2400000 -i -G mydata Hope this will be useful for somebody as it was for me. If you will accept the patch - please, update the windows binaries. Thanks, psb. ------------------------------------------------------------------------------- diff --git a/src/rtl_sdr.c b/src/rtl_sdr.c index eeb6dba..3564329 100644 --- a/src/rtl_sdr.c +++ b/src/rtl_sdr.c @@ -42,6 +42,7 @@ static int do_exit = 0; static uint32_t bytes_to_read = 0; static rtlsdr_dev_t *dev = NULL; +static int samp_mode = 0; void usage(void) { @@ -54,6 +55,9 @@ void usage(void) "\t[-b output_block_size (default: 16 * 16384)]\n" "\t[-n number of samples to read (default: 0, infinite)]\n" "\t[-S force sync output (default: async)]\n" + "\t[-i set direct sampling mode (I)]\n" + "\t[-q set direct sampling mode (Q)]\n" + "\t[-G use RTL automatic gain]\n" "\tfilename (a '-' dumps samples to stdout)\n\n"); exit(1); } @@ -81,6 +85,8 @@ static void sighandler(int signum) static void rtlsdr_callback(unsigned char *buf, uint32_t len, void *ctx) { + uint32_t i, r; + unsigned char *p1, *p2; if (ctx) { if (do_exit) return; @@ -91,7 +97,16 @@ static void rtlsdr_callback(unsigned char *buf, uint32_t len, void *ctx) rtlsdr_cancel_async(dev); } - if (fwrite(buf, 1, len, (FILE*)ctx) != len) { + if (samp_mode) { + // For direct sampling mode we throw out each 2nd value, + // i.e., save only one channel data - I or Q. + for (i=0, p1=buf, p2=buf; i<len; i+=2, p2++) + *p1++ = *p2++; + r = (fwrite(buf, 1, len/2, (FILE*)ctx) == len/2); + } else + r = (fwrite(buf, 1, len, (FILE*)ctx) == len); + + if (!r) { fprintf(stderr, "Short write, samples lost, exiting!\n"); rtlsdr_cancel_async(dev); } @@ -119,8 +134,10 @@ int main(int argc, char **argv) uint32_t out_block_size = DEFAULT_BUF_LENGTH; int device_count; char vendor[256], product[256], serial[256]; + uint32_t use_rtlagc = 0; + unsigned char *p1, *p2; - while ((opt = getopt(argc, argv, "d:f:g:s:b:n:S::")) != -1) { + while ((opt = getopt(argc, argv, "d:f:g:s:b:n:S::Gqi")) != -1) { switch (opt) { case 'd': dev_index = atoi(optarg); @@ -143,6 +160,15 @@ int main(int argc, char **argv) case 'S': sync_mode = 1; break; + case 'q': + samp_mode = 2; + break; + case 'i': + samp_mode = 1; + break; + case 'G': + use_rtlagc = 1; + break; default: usage(); break; @@ -205,6 +231,15 @@ int main(int argc, char **argv) if (r < 0) fprintf(stderr, "WARNING: Failed to set sample rate.\n"); + /* Set direct sampling */ + if (samp_mode) { + r = rtlsdr_set_direct_sampling(dev, samp_mode); + if (r < 0) + fprintf(stderr, "WARNING: Failed to set direct sampling mode.\n"); + else + fprintf(stderr, "Tuner set to direct sampling mode (%c).\n", (samp_mode==1)?'I':'Q'); + } + /* Set the frequency */ r = rtlsdr_set_center_freq(dev, frequency); if (r < 0) @@ -231,6 +266,21 @@ int main(int argc, char **argv) fprintf(stderr, "Tuner gain set to %f dB.\n", gain/10.0); } + /* Set RTL automatic gain */ + if (1 == use_rtlagc) { + /* Enable automatic RTL gain */ + r = rtlsdr_set_agc_mode(dev, 1); + if (r < 0) + fprintf(stderr, "WARNING: Failed to enable RTL automatic gain.\n"); + else + fprintf(stderr, "RTL automatic gain enabled.\n"); + } else { + /* Disable automatic RTL gain */ + r = rtlsdr_set_agc_mode(dev, 0); + if (r < 0) + fprintf(stderr, "WARNING: Failed to disable RTL automatic gain.\n"); + } + if(strcmp(filename, "-") == 0) { /* Write samples to stdout */ file = stdout; #ifdef _WIN32 @@ -263,7 +313,16 @@ int main(int argc, char **argv) do_exit = 1; } - if (fwrite(buffer, 1, n_read, file) != (size_t)n_read) { + if (samp_mode) { + // For direct sampling mode we throw out each 2nd value, + // i.e., save only one channel data - I or Q. + for (i=0, p1=buffer, p2=buffer; i<n_read; i+=2, p2++) + *p1++ = *p2++; + r = (fwrite(buffer, 1, n_read/2, file)== n_read/2); + } else + r = (fwrite(buffer, 1, n_read, file) == n_read); + + if (!r) { fprintf(stderr, "Short write, samples lost, exiting!\n"); break; }

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rtl-sdr on Nokia n900 phones
by Fritz Wuehler 14 Sep '13

14 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.

3 3

rtl_fm, rtl_power, mingw, r820t
by keenerd 14 Sep '13

14 Sep '13

Hey all. I've been shouting it all over /r/rtlsdr and ##rtlsdr, but just for you fine folks that are only on the ML, here[1] is what I've been up to the past week: Overhauled scanning in rtl_fm. This fixed a number of issues, where either scanning did not work at all and some brokenness on OpenBSD. It also meant giving up on the async API entirely. Released a whole new application, rtl_power. This is something I'd had bouncing around on my hard drive for many months, half-unwritten due to over-complexity. It'll generate CSV files of arbitrarily slow/wide/detailed FFTs. Also a little visualization script[2] that won't choke when you give it 50,000 columns of data. In the process of testing rtl_power, two more things came up. First was windows builds. I've got a half-finished mingw32 build script[3] that'll let me produce windows binaries[4] on a linux host. These have been confirmed to actually run and probably work. Only W32 for now, but just because I was too lazy to build the W64 toolchain. Second was the discovery[5] that scanning had gotten a whole lot slower since my original experiments with rtl_fm. 85mS to retune is unacceptably slow. Since the r820t driver is the slowest, I started looking into figuring out what is going on. Still figuring that out but I have done basic cleanups to the code (removing redundancy, particularly around register writes) and the driver is 15% shorter with no modifications to code behavior. I would not mind talking to Steve or one of the other devs on IRC about some of the more ambiguous aspects of the driver. (Like, why some reg writes are backed up to R828_Arry[] and others aren't. And is that array thread safe at all? If not I'll have to do some very large changes to support multiple dongles in rtl_power.) I would really like to get these changes merged, particularly the rtl_fm stuff because the version in the official repo is rather bit-rotten. -Kyle http://kmkeen.com [1] https://github.com/keenerd/rtl-sdr [2] http://www.reddit.com/r/RTLSDR/comments/1ktzwi/ [3] http://kmkeen.com/tmp/mingw32.sh.txt [4] http://kmkeen.com/tmp/rtl-sdr-mingw32-2013-08-28.zip [5] http://www.reddit.com/r/RTLSDR/comments/1l2vlx/

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[PATCH] rtl_adsb: Fix invalid memory access
by Will Glynn 14 Sep '13

14 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 10 Sep '13

10 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 09 Sep '13

09 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 03 Sep '13

03 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

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osmocom-sdr September 2013