Hi The clocks we would be using are *much* better than what most military systems use….
I also *assume* that an initial lock up that takes a hour is perfectly acceptable in this application. You will still need a lot of hours / days / what ever of data to get useful stability off of WWVB, spending an hour or more to acquire from a cold start will have little net impact. Bob On Jul 8, 2012, at 7:29 PM, J. Forster wrote: > 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 -- time-nuts@febo.com >>>>>> To unsubscribe, go to >>>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>>>> and follow the instructions there. >>>>> >>>>> >>>>> >>>>> _______________________________________________ >>>>> time-nuts mailing list -- time-nuts@febo.com >>>>> To unsubscribe, go to >>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>>> and follow the instructions there. >>>>> >>>> >>>> _______________________________________________ >>>> time-nuts mailing list -- time-nuts@febo.com >>>> To unsubscribe, go to >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>> and follow the instructions there. >>>> >>>> >>> >>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.