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 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
