I ran the volk profile generator, but with the resulting volk_config file (all other settings untouched) I don't get any audio out of gqrx
On Tue, Jun 2, 2015 at 11:32 AM, Philip Balister <phi...@balister.org> wrote: > On 06/02/2015 11:22 AM, West, Nathan wrote: >> I've heard a complaint about something similar on ARM before that was VOLK >> related. Can you set your volk_config to use the neon for >> volk_32f_x2_dot_prod_32f and report back? >> >> If the previous request is confusing just copy this file [0] to >> ~/.volk/volk_config. >> >> [0] >> https://raw.githubusercontent.com/balister/meta-sdr/f1ce8601482655695cb27b06aefbf9a620a27bd0/recipes-support/volk/files/ettus-e300/volk_config > > That is the output of volk_profile run on an E310. You may get better > results running volk_profile on your hardware. Then making the change > Nathan suggests. > > Philip > >> >> I'm interested in results and can provide more detailed steps in a few >> hours if needed. >> >> -Nathan >> >> On Tue, Jun 2, 2015 at 10:29 AM, Stephan van Beerschoten < >> step...@vanbeerschoten.net> wrote: >> >>> Let me add that I don't know anything about the signal, other than that >>> it's broadcast on 155.520MHz. >>> >>> On Tue, Jun 2, 2015 at 3:19 AM, Marcus Müller <marcus.muel...@ettus.com> >>> wrote: >>> >>>> Hi Stephan, >>>> >>>> I am sure GR can do that, but I can't ;-) >>>> >>>> I can't help but propose you change that ;) No, seriously, >>>> cross-compiling GNU Radio for an ARM sounds more complicated than doing >>>> non-coherent binary FSK demod, but then again, that might just be me :D. >>>> >>>> In fact, you're absolutely right: getting a solid signal quality before >>>> attempting decoding might be a good idea. However, most probably pagers >>>> don't need awesome SNR, so "somewhat noisy" might still be ok. >>>> >>>> so how do you get the samples into GNU Radio? >>>> I guess you use the gr-osmosdr source? which sampling rate? Where in your >>>> base band are your carriers? >>>> What does your flow graph look like? >>>> >>>> Generally: If you have a RF recording, [1] might just profit from one >>>> more entry, and we'd have something more tangible to talk about :) >>>> >>>> I'll outline the steps I'd do to try to achieve better signal: >>>> >>>> >>>> 1. Record a signal and test with that -- doing everything live makes >>>> things complicated and hard to reproduce. >>>> 2. Use a xlating FIR filter to move a single 12.5kHz channel to 0Hz, >>>> so that either symbol is +- 4.5kHz >>>> 1. this will require that you design a filter. Don't worry, that's >>>> relatively easy: >>>> 1. run gr_filter_design >>>> 2. select low pass, enter your source's sampling rate, set the >>>> end of the pass band to let's say 5kHz and the start of the stop >>>> band to >>>> 7.5kHz (If I understand wikipedia correctly, channel spacing is >>>> 12.5kHz, >>>> and symbol deviation is +-4.5kHz, so from the center of the lower >>>> channel >>>> to the lower bit of the upper channel it's 12.5kHz - 4.5kHz = >>>> 8kHz). >>>> 3. You'll notice that if you start with a high sampling rate, >>>> your filter gets ridiculously long. If that's the case, you might >>>> want to >>>> reduce the sampling rate of your signal source, or add a stage of >>>> half- or >>>> quarter bandwidth FIR decimation (with a decimation factor of 2 >>>> or 4, >>>> respectively) >>>> 2. set the decimation of that xlating FIR to something reasonable, >>>> so that rate_in/decimation > 12.5kHz/2, but not >>. >>>> 1. this way, you'll get "just enough" rate at the output. >>>> 3. set the center frequency to the middle of your two symbol >>>> frequencies in the input spectrum >>>> 3. add visualization sinks here and there, and verify :) >>>> 4. add a real high-pass filter >>>> 1. Your single-channel spectrum looks something like [1] with 0 Hz >>>> in the middle. Since we've filtered away stuff above 5kHz, we'd now >>>> concern ourselves with filtering away everything below 4kHz. >>>> 2. Same procedure as for the xlating fir, but use the reduced >>>> sampling rate and a 4 kHz high-pass with a 2kHz stop band or >>>> something. The >>>> closer the stop band is to pass band, the longer your filter gets. >>>> 3. In principle, a 4-5 kHz real-tapped bandpass xlating fir would >>>> have done the same, but doing this step by step reduces error >>>> probability. >>>> 5. repeat "add visualizations" :) >>>> 6. You should now have a clean signal with only two peaks in your >>>> spectrum at +-4.5kHz; does your external decoder deal well with that? >>>> >>>> In principle, you're extremely close to having your own decoder by now. >>>> Non-coherent BFSK decoding would simply do the same as step 2, but with two >>>> filters, each centered on either symbol frequency, baudrate-wide passband, >>>> decimating to the baudrate, followed by a complex-to-magnituded-squared >>>> conversion each, then something like division of the 1-filter magsquared by >>>> the 0-filter magsquared, followed by a threshold decision (threshold=1). >>>> You'd then be getting a raw POCSAG bitstream :D >>>> Best regards, >>>> Marcus >>>> >>>> >>>> [1] from http://edge.rit.edu/edge/P09141/public/FSK.pdf , >>>> Watkins-Johnson Company "Tech-notes Vol. 7 No. 5 September/October 1980: >>>> FSK: Signals and Demodulation", p. 8 [image: FSK spectrum] >>>> <http://edge.rit.edu/edge/P09141/public/FSK.pdf> >>>> >>>> On 06/02/2015 12:04 AM, Stephan van Beerschoten wrote: >>>> >>>> I am sure GR can do that, but I can't ;-) >>>> Also, I don't have a good waterfall at all of the pocsag broadcast, which >>>> is probably part of why I can't make it out with my ears either. Yes, I >>>> think I have too much noise. >>>> I hope it can be overcome with the right settings and filters. >>>> >>>> I'll try to capture a screenshot of what I see. It's nothing like the >>>> screenshots in Wikipedia. >>>> On Jun 1, 2015 5:47 PM, "Marcus Müller" <marcus.muel...@ettus.com> wrote: >>>> >>>>> Hi! >>>>> I personally think the soundbite from wikipedia is broken, since it's >>>>> 11kHz sampling rate violates Nyquist ;) >>>>> Well, I must admit that my preferred way of analyzing this wouldn't be >>>>> the audible reproduction; if you can see it clearly on the waterfall, and >>>>> "optically" have enough dB between the carriers and noise, then you'll be >>>>> fine decoding it. >>>>> >>>>> Now, I trust you're actually seeing excessive noise -- this might point >>>>> to problems with your receiver (unsuitable antenna, too much noise in the >>>>> amplifier, too little gain, intermodulation). The first step in limiting >>>>> noise is always adding appropriate filtering. Can you add a FIR that >>>>> selects your POCSAG channel out of your sampling bandwidth? >>>>> >>>>> Best regards, >>>>> Marcus >>>>> >>>>> On 06/01/2015 11:28 PM, Stephan van Beerschoten wrote: >>>>> >>>>> You're right in that I need more than GR. The audio of a pocsag >>>>> broadcast is very distinct. It's also clearly visible on a waterfall. >>>>> The problem is that I have too much static in there. Way too much noise. >>>>> I can't get the gqrx module (where I tune and see the waterfall) set right >>>>> so the reception is fine. >>>>> I think the Wikipedia article had a soundbite of a pocsag encoding. If >>>>> you listen to it you'll notice it's very distinct.i just have 90% noise >>>>> and >>>>> I can hear the broadcast in the very background. >>>>> On Jun 1, 2015 5:25 PM, "Marcus Müller" <marcus.muel...@ettus.com> >>>>> wrote: >>>>> >>>>>> Hi again, >>>>>> >>>>>> Ok, I'm not familiar with the standard POCSAG, but if you got a signal >>>>>> that you still need to decode with something else, how do you know you >>>>>> don't get clear reception? What is your measure for "good reception"? >>>>>> >>>>>> As far as I read the English wikipedia, POCSAC uses a 4.5kHz binary >>>>>> FSK, so can you see the two alternating frequency e.g. in a waterfall >>>>>> plot >>>>>> of your RX signal? >>>>>> Ideally, you'd directly be able to see the 512, 1200 or 2400 baud. >>>>>> >>>>>> To explain a bit more: >>>>>> GNU Radio is not a decoder for any specific standard; think of it as >>>>>> the LEGO of SDR. You can build amazing things with it, in fact, there's a >>>>>> lot of examples that come with GNU Radio, and useful and complex standard >>>>>> implementations (FM receiver, DTV transmission!), but if you need to have >>>>>> something that's not there, you might need to a) use someone else's >>>>>> Out-Of-Tree module or b) implement that functionality yourself. So I must >>>>>> admit that I don't have the slightest idea which settings you're >>>>>> referring >>>>>> to :) Maybe you're interested in a quick&dirty introduction to GNU Radio >>>>>> [1]. >>>>>> >>>>>> In the case of POCSAG, I remember gr-pocsag being a thing (search for >>>>>> pocsag on cgran.org); I can't remember the original author, and I >>>>>> presume it's pretty much dead -- but I'd love to be proven wrong. >>>>>> Also, pyboms has pocsag-mrt package, but that seems to rely on GNU >>>>>> Radio 3.6.2, if the Readme is correct, so that's pretty dead, too. >>>>>> >>>>>> >>>>>> Best regards, >>>>>> Marcus >>>>>> >>>>>> [1] https://github.com/iZsh/pocsag-mrt >>>>>> On 06/01/2015 10:18 PM, Stephan van Beerschoten wrote: >>>>>> >>>>>> It is. I plan on running the output through a utility that can decode >>>>>> it. However, before that can happen I need to find out how I can get a >>>>>> clear reception of the broadcast. >>>>>> On Jun 1, 2015 4:15 PM, "Marcus Müller" <marcus.muel...@ettus.com> >>>>>> wrote: >>>>>> >>>>>>> I'm a bit confused, I though POCSAG was a text pager system? >>>>>>> >>>>>>> On 06/01/2015 10:04 PM, Stephan van Beerschoten wrote: >>>>>>>> Hi Guys, >>>>>>>> >>>>>>>> I compiled gnuradio for my ODROID ARM platform, and I can listen to >>>>>>>> regular wideband radio just fine. I am using a Generic RTL2832U with >>>>>>>> Rafael Micro R820T tuner. >>>>>>>> >>>>>>>> The radio quality is fine, and even when using the rtl_fm tool >>>>>>>> directly (off topic for this list), it works. >>>>>>>> >>>>>>>> However, when I switch channels to 155.520 to capture POCSAG >>>>>>>> broadcasts I cannot get a clear reception. I can't find any decent >>>>>>>> documentation on GR to tell me what each setting is, and I am not a >>>>>>>> HAM radio operator so some of the basics evade me. >>>>>>>> >>>>>>>> I can't get decent POCSAG reception with the rtl_fm tool either, so >>>>>>>> this is probably a setting thing somewhere. >>>>>>>> >>>>>>>> Why can't I get clear reception? Any pointers? >>>>>>>> >>>>>>>> Stephan >>>>>>>> >>>>>>>> _______________________________________________ >>>>>>>> Discuss-gnuradio mailing list >>>>>>>> Discuss-gnuradio@gnu.org >>>>>>>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>>>>>> >>>>>>> >>>>>>> _______________________________________________ >>>>>>> Discuss-gnuradio mailing list >>>>>>> Discuss-gnuradio@gnu.org >>>>>>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>>>>>> >>>>>> >>>>>> >>>>> >>>> >>> >>> _______________________________________________ >>> Discuss-gnuradio mailing list >>> Discuss-gnuradio@gnu.org >>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> >>> >> >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
