Hey Stephan, probably, you've even got a fully fledged GR installation around. If not, I'd say: get the uber-cool LiveSDR DVD image [1], boot from it. As soon as you have a full GR installation, you can run the GNU Radio companion, which feels a lot like connecting together "real world filters" with "cables".
Actually, how many messages did you get in your firefighting days? Back in my catastrophe protection service time, I didn't have a pager, but I remember these things rarely going off -- luckily, not too many catastrophes around southern Germany. That's why I didn't try getting the signal myself -- I didn't assume I had a good chance of seeing it. Best regards, Marcus [1] http://gnuradio.org/redmine/news/52 On 06/02/2015 04:24 PM, Stephan van Beerschoten wrote: > I've been an IT geek for over 15 years, but the frequency chatter and > filter settings are daunting to me. About 10 years ago almost got my > HAM radio license to up my personal geek factor, but I couldn't get > myself to learn the electronic circuitry needed. I bow before you :) > > To answer your question: I only use gqrx (http://gqrx.dk/) right now, > and I just realized it's something built on top of GR and not GR > itself. > This tool doesn't really allow any custom filters. It's a use as-is > kinda tool, but it has a lot of options. > > I mean, it could just be that my physical location is just not that > good to receive these localized (county-wide only) pager broadcasts. > When I still had my fire department pager I remember that I'd > sometimes get a few alphanumeric characters garbled, indicating bad > reception. I would like to try and improve the SNR to make the > decoding work. > > > > On Tue, Jun 2, 2015 at 2:13 AM, Marcus Müller <marcus.muel...@ettus.com> > wrote: >> Hi Stephan, >> >> so how do you get the samples into GNU Radio? >> I guess you use the gr-osmosdr source? >> What does your flow graph look like? >> >> Best regards, >> Marcus >> >> >> 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
