On 26 May 2015 03:28, "Robert McGwier" <rwmcgw...@gmail.com> wrote: > > [...] > That said, hackers (the good definition) live for this, and I encourage it.
Just wanted to emphasise this. Go for it! Worst case, you learn a lot of interesting things. Cheers, M > > Bob > > > On Tue, May 19, 2015 at 3:04 PM, Mark Haun <hau...@keteu.org> wrote: >> >> This is a bit of an idle question, but I'm hoping some knowledgable folks on >> here can offer advice. Mostly I'm trying to understand better what I >> don't know, and the size of the challenge, before jumping in to a project: >> >> I'd like to try decoding some AVL traffic in the 700-MHz band (GPS locations >> broadcast by transit vehicles to a central collector, where predictors are >> used to generate the ETAs displayed on electronic bus-stop signs). The >> modulation is 4-FSK, similar to P25 except wider with a higher symbol rate, >> emission designator 20K0F1D. The particular frequency(s) should be easy >> enough to discover. Transmissions are short packets on shared channels with >> some kind of slotted aloha or CSMA MAC. A rate-3/4 convolutional code is >> used. The preceding is public information gleaned from the web. I haven't >> captured any signals yet. >> >> The known unknowns: preambles and framing stuff, symbol mapping, >> the particular rate-3/4 code used (only a couple of candidates though), and, >> the scrambler (whitener) and its initialization. AFAIK there is no >> encryption per se. The payload is supposed to be TCP/IP, so there could be >> some sort of header compression. >> >> My question, then, is given this information, are there reasonable odds of >> success? I have some digital comms background from grad school but little >> to no practical experience. Wondering if this might be an excuse to pick up >> a HackRF etc. and learn GNU Radio, or if it's likely to be a dead end. >> >> Thanks, >> >> Mark >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > > -- > Bob McGwier > Co-Founder and Technical Director, Federated Wireless, LLC > Research Professor Virginia Tech > Senior Member IEEE, Facebook: N4HYBob, ARS: N4HY > Faculty Advisor Virginia Tech Amateur Radio Assn. (K4KDJ) > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >
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