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
