Re: SDR FM demodulation
Hi, On 11.02.2012 13:46, Antti Palosaari wrote: Now someone should make Linux driver that can tune that device to different frequencies and look what it really can do. I sniffed the Windows driver and wrote a small libusb-based program [1], which can tune to a given frequency and record the I/Q-samples to a file. So far FM radio reception with GNU Radio, as well as GMR-1 satellite (Thuraya) reception [2] at 1,525GHz with 1,8MHz bandwidth have been tested. Despite the 8 bit ADC, the stick seems to perform quite well. The program so far supports the ezcap USB 2.0 DVB-T/DAB/FM stick with the Elonics E4000 tuner, and the Terratec NOXON DAB/DAB+ USB-Stick with the Fitipower FC0013 tuner. The code is still somewhat hackish and experimental, since not all of the demodulator registers are known, and especially the tuner setup has room for improvement. Regards, Steve [1] http://cgit.osmocom.org/cgit/rtl-sdr/ [2] http://gmr.osmocom.org/ -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: SDR FM demodulation
On Sat, Feb 11, 2012 at 07:00:16AM +, Alistair Buxton wrote: The source file appears to be about 2 to 2.2 million samples per second. Any higher than that and the person speaking sounds like a chipmunk. Maybe 22050 * 1000 or 1024? Does any Finnish station broadcast pips like the BBC does? That could be used to determine the actual rate. The stereo carrier is at 19kHz and RDS is centered around 57kHz. I'd say this is 2048kHz sampling rate. Daniel -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: SDR FM demodulation
On 11.02.2012 09:00, Alistair Buxton wrote: On 9 February 2012 15:01, Antti Palosaaricr...@iki.fi wrote: Decode it and listen some Finnish speak ;) Done. grc and output.wav here: http://al.robotfuzz.com/~al/rtl2832/ The trick was realising that the UChar to Float converter does not adjust it's output to the range -1.0,1.0 that the wideband FM demodulator block expects as input. Once I figured that out the rest was easy. Just set the quadrature rate to the samples per second in the source file, and the decimation to quadrature rate/output sink rate. The source file appears to be about 2 to 2.2 million samples per second. Any higher than that and the person speaking sounds like a chipmunk. Maybe 22050 * 1000 or 1024? Does any Finnish station broadcast pips like the BBC does? That could be used to determine the actual rate. Cool! I did that whole last night up to 6 am. I also ended up very similar blocks, but failed to convert bytes as UChar. I tried to add constant between Deinterleave and UChar To Float but it wasn't possible. So my first idea was to make Python script to make for the sample when I wake-up. But no need anymore :) It was very good learning session and I am very impressed about GNU Radio capability. Idea tool for learning signal handling in practise. I see that device has big potential for students as it is very cheap SDR, everyone can get own! Now someone should make Linux driver that can tune that device to different frequencies and look what it really can do. What kind of driver architecture should be used? Use device 100% userspace or make it working as Kernel driver? I suspect making it as Kernel driver could be too limited since V4L/DVB API restrictions? regards Antti -- http://palosaari.fi/ -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: SDR FM demodulation
On Sat, Feb 11, 2012 at 02:46:34PM +0200, Antti Palosaari wrote: I did that whole last night up to 6 am. I also ended up very similar blocks, but failed to convert bytes as UChar. I tried to add constant between Deinterleave and UChar To Float but it wasn't possible. So my first idea was to make Python script to make for the sample when I wake-up. But no need anymore :) I ended up writing a FM demodulator in C before I found Alistair's mail in my inbox. Using a 65536 element table for arc tangent and integer arithmetics, it is pretty fast. Now someone should make Linux driver that can tune that device to different frequencies and look what it really can do. What kind of driver architecture should be used? Use device 100% userspace or make it working as Kernel driver? I suspect making it as Kernel driver could be too limited since V4L/DVB API restrictions? There is also the CX23880/1/2/3 series with two 10 bit ADCs (usually) sampling at 28.7MHz. The video part can be switched to raw mode, where it provides 8 bit samples at full or 16 bit samples at half the sampling rate from the luma ADC. In non-Y/C mode the chroma ADC is used by the audio part, where the data can be fed through a configurable chain of filters, demodulatos, and sample rate converters. Just grep 0x320 cx88-reg.h to get a glimpse of its capabilities. There is absolutely no documentation to be found about most of these registers. A reconfigurable silicon tuner like the XC3028 again increases the number of possibilities by a large factor. BT87x aka CX2587x is used for SDR as well, but its video raw mode is good just for analog tv signals, as it expects vsyncs and the audio ADC usually just samples the tuner's baseband sound output at 448kHz. Some variants claim to support FM stereo and BTSC decoding capabilities, but AFAIR there is no support in the Linux driver and the public data sheet just tells us there is a DAP between the decimation filter and the DMA FIFO. If only there was completely open documentation... All in all, I don't think there can be one API that fits all devices without limiting their functionality. Maybe a UVC or LabVIEW like interface with blocks for tuners, ADCs, decimators, DMA sinks, etc. is suitable, but then applications will end up being tailored to a small number of topologies or require manual configuration. For most people the only use would probably be to listen to FM radio. Daniel -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: SDR FM demodulation
On 11.02.2012 17:15, Daniel Glöckner wrote: All in all, I don't think there can be one API that fits all devices without limiting their functionality. Maybe a UVC or LabVIEW like interface with blocks for tuners, ADCs, decimators, DMA sinks, etc. is suitable, but then applications will end up being tailored to a small number of topologies or require manual configuration. For most people the only use would probably be to listen to FM radio. For me I would like to see that more interesting SDR than FM radio :) I should look how famous USRP/USRP2 are connected to the GNU Radio and maybe try similar approach. I think it is userspace interface but it fits fine. It is always possible load device us normal Kernel driven DVB-T and if user like to use it as SDR then user should blacklist just kernel driver. I opened my device and there is Elonics E4000 [1] silicon tuner. That tuner seems to be a little crazy beast! Supports frequencies from 64 to 1678 MHz and very many modulations. So for my eyes it is almost idea cheap SDR. No idea what is supported max bw ADC can sample... DVB-T (174-240MHz, 470-854MHz) ISDB-T (470-862MHz) DVB-H (470-854MHz, 1672-1678MHz) CMMB (470-862MHz) D-TMB (470-862MHz) T-DMB (174-240MHz, 1452-1492MHz) DAB (174-240MHz, 1452-1492MHz) MediaFLO (470-862, 1452-1492MHz) GPS L1 band (1575MHz) FM radio (64-108MHz) [1] http://www.elonics.com/product.do?id=1 regards Antti -- http://palosaari.fi/ -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: SDR FM demodulation
On Sat, Feb 11, 2012 at 05:33:05PM +0200, Antti Palosaari wrote: I opened my device and there is Elonics E4000 [1] silicon tuner. That tuner seems to be a little crazy beast! Supports frequencies from 64 to 1678 MHz and very many modulations. So for my eyes it is almost idea cheap SDR. No idea what is supported max bw ADC can sample... I just tried to find the XC3028 product brief. It seems XCeive has recently been bought by a company called CrestaTech that have a USB/PCIe chipset for a small universal receiver and a PC based SDR suite for TV/radio/GPS decoding. Daniel -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: SDR FM demodulation
On Fri, 2012-02-10 at 20:29 -0600, David Hagood wrote:
On Fri, 2012-02-10 at 21:08 -0500, Andy Walls wrote:
Randomly checking some of the data with GNUplot, if 2.5 Msps is the
sampling rate, then the fastest freq I saw was about 50 kHz.
How'd you analyze the data - assume it was baseband I/Q and do an FFT?
If so, and if this was digitized baseband, you should have seen the FM
stereo pilot tone at 19kHz.
Well, I was examining the data in the time-domain using 'od' to decode
the bytes to text and using gnuplot to visualize. I looked for high
frequency contant envelope cycles. Pretty lame, I know.
I did this in octave this morning and noted a carrier/pilot of some
sort:
fid = fopen('rtl2832u_fm_sample_FIXED.bin');
N=2^20;
fseek(fid, N*10, SEEK_SET);
[v, count] = fread(fid,[2,N],'unsigned char');
v = (v-128)/128;
w = v(1,:) + j*v(2,:);
f = fft(v(1,:),N);
fw = fft(v(1,:),N);
Fs = 2.5e6;
freqs = [1:(N/24)-1]*Fs/N;
bins = [2:N/24];
plot(freqs, abs(f(bins))/N, '.');
plot(freqs, abs(fw(bins))/N, '.');
[m,mi] = max(abs(fw)/N);
freqs(mi)
ans = 9534.4
[m,mi] = max(abs(f)/N);
freqs(mi)
ans = 9534.4
ans*2/1000
ans = 19.069
I must have Fs wrong.
Anyway not much happens in the data above 100 kHz, but to see the whol
spectrum:
bins = [2:N/2];
freqs = [1:(N/2)-1]*Fs/N;
semilogy(freqs, abs(f(bins))/N, '.');
semilogy(freqs, abs(fw(bins))/N, '.');
But it appears someone has now already solved the decoding problem.
Regards,
Andy
If it's digitized IF, you should be able to run it through a rectangular
to polar conversion (compute mag = I^2+Q^2 and phase = arctan(I/Q) (use
a proper 4 quadrant arctan), then compute frequency by the delta between
the phase samples. Mag should be constant, frequency would then be your
audio.
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Re: SDR FM demodulation
On Thu, 2012-02-09 at 17:21 +0200, Antti Palosaari wrote: On 09.02.2012 17:11, Patrick Boettcher wrote: On Thursday 09 February 2012 16:01:12 Antti Palosaari wrote: I have taken radio sniffs from FM capable Realtek DVB-T device. Looks like demodulator ADC samples IF frequency and pass all the sampled data to the application. Application is then responsible for decoding that. Device supports DVB-T, FM and DAB. I can guess both FM and DAB are demodulated by software. Here is 17 second, 83 MB, FM radio sniff: http://palosaari.fi/linux/v4l-dvb/rtl2832u_fm/ Decode it and listen some Finnish speak ;) Could someone help to decode it? I tried GNU Radio, but I failed likely because I didn't have enough knowledge... GNU Radio and Octave or Matlab are way to go. For someone to decode it, you would need to give more information about the format of the stream. Like the sampling frequency, the sample-format and then the IF-frequency. You can see sampling format easily looking hexdump or open file in Audacity. It is 8bit unsigned samples, 2 channels (I Q). No knowledge about IF... For good guess is to try some general used IFs. Sampling freq can be calculated using sample info and the fact it is about 17 sec. sample size = 86919168 Bytes, time 17 sec. 2 channels, 1 byte sample = 2556446,11765 sample/sec (~2.5 MHz!) Randomly checking some of the data with GNUplot, if 2.5 Msps is the sampling rate, then the fastest freq I saw was about 50 kHz. Maybe you have an FM compsite baseband signal: http://en.wikipedia.org/wiki/FM_broadcast#Other_subcarrier_services If you low pass filter with digital filter with (an equivalent to) a 17 kHz cutoff, you may just be left with the mono L+R channel. I am assuming the IQ channels in the data are 8 bit LPCM so x = (c-128)/128.0 normalizes an usigned byte sample value c in 0 to 255 to a float value x in -1.0 to 1.0. Regards, Andy I never did something like myself, but from what I saw in gnuradio there should be everything to make a FM-demod based on the data. Yes there was a lot of block and those were rather easy to connect using graphical interface (gnuradio-companion). But I don't know exactly what block are needed and what are parameters. I used file-sink = fm-modulator = audio-sink. Likely not enough :i Without any earlier experience it is rather challenging. But if there is someone who have done that earlier using USRP SDR he could likely do it easier :) regards Antti -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: SDR FM demodulation
On Fri, 2012-02-10 at 21:08 -0500, Andy Walls wrote: Randomly checking some of the data with GNUplot, if 2.5 Msps is the sampling rate, then the fastest freq I saw was about 50 kHz. How'd you analyze the data - assume it was baseband I/Q and do an FFT? If so, and if this was digitized baseband, you should have seen the FM stereo pilot tone at 19kHz. If it's digitized IF, you should be able to run it through a rectangular to polar conversion (compute mag = I^2+Q^2 and phase = arctan(I/Q) (use a proper 4 quadrant arctan), then compute frequency by the delta between the phase samples. Mag should be constant, frequency would then be your audio. -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: SDR FM demodulation
On 9 February 2012 15:01, Antti Palosaari cr...@iki.fi wrote: Decode it and listen some Finnish speak ;) Done. grc and output.wav here: http://al.robotfuzz.com/~al/rtl2832/ The trick was realising that the UChar to Float converter does not adjust it's output to the range -1.0,1.0 that the wideband FM demodulator block expects as input. Once I figured that out the rest was easy. Just set the quadrature rate to the samples per second in the source file, and the decimation to quadrature rate/output sink rate. The source file appears to be about 2 to 2.2 million samples per second. Any higher than that and the person speaking sounds like a chipmunk. Maybe 22050 * 1000 or 1024? Does any Finnish station broadcast pips like the BBC does? That could be used to determine the actual rate. -- Alistair Buxton a.j.bux...@gmail.com -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
SDR FM demodulation
I have taken radio sniffs from FM capable Realtek DVB-T device. Looks like demodulator ADC samples IF frequency and pass all the sampled data to the application. Application is then responsible for decoding that. Device supports DVB-T, FM and DAB. I can guess both FM and DAB are demodulated by software. Here is 17 second, 83 MB, FM radio sniff: http://palosaari.fi/linux/v4l-dvb/rtl2832u_fm/ Decode it and listen some Finnish speak ;) Could someone help to decode it? I tried GNU Radio, but I failed likely because I didn't have enough knowledge... GNU Radio and Octave or Matlab are way to go. I smell very cheap poor man's software radio here :) regards Antti -- http://palosaari.fi/ -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: SDR FM demodulation
On Thursday 09 February 2012 16:01:12 Antti Palosaari wrote: I have taken radio sniffs from FM capable Realtek DVB-T device. Looks like demodulator ADC samples IF frequency and pass all the sampled data to the application. Application is then responsible for decoding that. Device supports DVB-T, FM and DAB. I can guess both FM and DAB are demodulated by software. Here is 17 second, 83 MB, FM radio sniff: http://palosaari.fi/linux/v4l-dvb/rtl2832u_fm/ Decode it and listen some Finnish speak ;) Could someone help to decode it? I tried GNU Radio, but I failed likely because I didn't have enough knowledge... GNU Radio and Octave or Matlab are way to go. For someone to decode it, you would need to give more information about the format of the stream. Like the sampling frequency, the sample-format and then the IF-frequency. I never did something like myself, but from what I saw in gnuradio there should be everything to make a FM-demod based on the data. regards, -- Patrick Boettcher Kernel Labs Inc. http://www.kernellabs.com/ -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: SDR FM demodulation
On 09.02.2012 17:11, Patrick Boettcher wrote: On Thursday 09 February 2012 16:01:12 Antti Palosaari wrote: I have taken radio sniffs from FM capable Realtek DVB-T device. Looks like demodulator ADC samples IF frequency and pass all the sampled data to the application. Application is then responsible for decoding that. Device supports DVB-T, FM and DAB. I can guess both FM and DAB are demodulated by software. Here is 17 second, 83 MB, FM radio sniff: http://palosaari.fi/linux/v4l-dvb/rtl2832u_fm/ Decode it and listen some Finnish speak ;) Could someone help to decode it? I tried GNU Radio, but I failed likely because I didn't have enough knowledge... GNU Radio and Octave or Matlab are way to go. For someone to decode it, you would need to give more information about the format of the stream. Like the sampling frequency, the sample-format and then the IF-frequency. You can see sampling format easily looking hexdump or open file in Audacity. It is 8bit unsigned samples, 2 channels (I Q). No knowledge about IF... For good guess is to try some general used IFs. Sampling freq can be calculated using sample info and the fact it is about 17 sec. sample size = 86919168 Bytes, time 17 sec. 2 channels, 1 byte sample = 2556446,11765 sample/sec (~2.5 MHz!) I never did something like myself, but from what I saw in gnuradio there should be everything to make a FM-demod based on the data. Yes there was a lot of block and those were rather easy to connect using graphical interface (gnuradio-companion). But I don't know exactly what block are needed and what are parameters. I used file-sink = fm-modulator = audio-sink. Likely not enough :i Without any earlier experience it is rather challenging. But if there is someone who have done that earlier using USRP SDR he could likely do it easier :) regards Antti -- http://palosaari.fi/ -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: SDR FM demodulation
Antti Palosaari cr...@iki.fi wrote: On 09.02.2012 17:11, Patrick Boettcher wrote: On Thursday 09 February 2012 16:01:12 Antti Palosaari wrote: I have taken radio sniffs from FM capable Realtek DVB-T device. Looks like demodulator ADC samples IF frequency and pass all the sampled data to the application. Application is then responsible for decoding that. Device supports DVB-T, FM and DAB. I can guess both FM and DAB are demodulated by software. Here is 17 second, 83 MB, FM radio sniff: http://palosaari.fi/linux/v4l-dvb/rtl2832u_fm/ Decode it and listen some Finnish speak ;) Could someone help to decode it? I tried GNU Radio, but I failed likely because I didn't have enough knowledge... GNU Radio and Octave or Matlab are way to go. For someone to decode it, you would need to give more information about the format of the stream. Like the sampling frequency, the sample-format and then the IF-frequency. You can see sampling format easily looking hexdump or open file in Audacity. It is 8bit unsigned samples, 2 channels (I Q). No knowledge about IF... For good guess is to try some general used IFs. Sampling freq can be calculated using sample info and the fact it is about 17 sec. sample size = 86919168 Bytes, time 17 sec. 2 channels, 1 byte sample = 2556446,11765 sample/sec (~2.5 MHz!) I never did something like myself, but from what I saw in gnuradio there should be everything to make a FM-demod based on the data. Yes there was a lot of block and those were rather easy to connect using graphical interface (gnuradio-companion). But I don't know exactly what block are needed and what are parameters. I used file-sink = fm-modulator = audio-sink. Likely not enough :i Without any earlier experience it is rather challenging. But if there is someone who have done that earlier using USRP SDR he could likely do it easier :) regards Antti -- http://palosaari.fi/ -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Implement a phased locked loop (phase comparator, low pass filter, and VCO) that is centered reasonably close to the IF. The output of the LPF of the PLL should be the demodulated signal, IIRC. Maybe this matlab (octave) file will help you: http://www.mathworks.com/matlabcentral/fileexchange/24167-simple-pll-demostration Regards, Andy -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
