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.
