A risky assumption, and a cold start could be tricky. Equatorial took many minutes to lock up, with a much higher data rate, and it did it by slowly sweeping the local clock.
Aside: That's why military spread spectrum systems like good local clocks. They lock up a whole lot faster that way. -John ================ > Hi > > In this case the data format and it's contents are highly "computable". If > you have a good local clock *and* an initial lock, the rest of what > follows is predictable. That of course assumes we know the real format . > > Bob > > On Jul 8, 2012, at 6:58 PM, J. Forster wrote: > >> Hi Peter, >> >> That's be the hard way, but yes, if the message BPSK coded is computable >> and of a known format. If the message contained more than time, like >> solar >> flux, it gets more complicated very rapidly. >> >> A similar thing was done with the Equatorial system 30+ years ago. In >> that >> case, each data bit was broken into something like 32 or 64 chips (I >> don't >> remember). There were two maximally distant, orthogonal chip patterns, >> representing 1 and 0. The incoming BPSK message went through a 0 or 180 >> degree switch, then the IF stages. The switch was driven from a local >> (known pattern) chip generator, so that if everything was synced up the >> narrow band IF would put out the 0 or 1 that had been encoded. BTW, this >> trick vastly improved the system S/N becaust it narrowed the receiver IF >> bandwidth many times. >> >> If the chip pattern is not known (fixed) or computable (like a correct >> TOD) things go to pot quickly. >> >> Rather than building such a kludge, it would be easier to use the locked >> clock in a newly designed receiver and phase compare that to your local >> standard directly. >> >> -John >> >> ================== >> >> >> >> >> >> >>> Any possibility of using the decoded signal to un-do the modulation and >>> feed the reconstituted signal to the older receiver? >>> >>> >>> >>> On 7/8/2012 12:56 PM, paul wrote: >>>> Ei >>>> Sorry if I have your name reversed. By taking this approach it >>>> eliminates the ability to use wwvb as a frequency reference because it >>>> destroys that traceability. >>>> Thats what we are trying to preserve. Or at least re-establish for the >>>> older phase measuring receivers. >>>> Regards >>>> Paul >>>> >>>> On 7/8/2012 12:10 PM, Tofurk Ei wrote: >>>>> If the changeover you are talking about is this one: >>>>> http://www.nist.gov/pml/newsletter/radio.cfm as a proof of concept a >>>>> DVB-T >>>>> dongle/upconverter combo could almost certainly handle PM easily to >>>>> output >>>>> whatever it encodes, when paired with gnuradio.. >>>>> >>>>> The RTL2832U chip might also be able to handle some low band signals >>>>> directly, using direct sampling. No upconverter. >>>>> >>>>> Regardless, then the data would be fed into gnuradio - the gnuradio >>>>> developers GUI is called "gnuradio companion" It has a nifty way of >>>>> doing >>>>> this kind of thing, one builds a "flow graph" where the actual >>>>> demodulation >>>>> is simply laid out graphically and tested. >>>>> >>>>> When everything works to one's satisfaction the file is saved and it >>>>> gets >>>>> compiled - then it can run - its basically a python script. >>>>> >>>>> If the modulation scheme is public, I think you can be almost certain >>>>> that >>>>> gnuradio might be quite useful to rapidly design a tool to demodulate >>>>> it. >>>>> Perhaps very quickly. >>>>> >>>>> For the money, one really couldn't hope to beat the flexibility of >>>>> this >>>>> combination in any other manner. If I were interested in trying this >>>>> I >>>>> would join the gnuradio mailing list and ask there. Perhaps the >>>>> answer is >>>>> surprisingly simple. >>>>> _______________________________________________ >>>>> time-nuts mailing list -- [email protected] >>>>> To unsubscribe, go to >>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>>> and follow the instructions there. >>>> >>>> >>>> >>>> _______________________________________________ >>>> time-nuts mailing list -- [email protected] >>>> To unsubscribe, go to >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>> and follow the instructions there. >>>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >>> >> >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
