Why not DCF. NIH. Just joking. Good comments that are detailed. The phase does not change every second though it can. There are many times when the phase sits for 3 or more seconds. The PLL TC is about 2-3 seconds on the older receivers so they tend to jump around never really locking or only for a few seconds. Now NIST has provided more detail then the earlier documents and that is that for at least 2 seconds at the top of the minute the carrier is at 0 phase. (It may actually be 3 seconds. There is a comment about the last second of the minute).
So what I have ended up doing along with discussions with JohnFor of time-nuts fame is use a inverting and non inverting path with switch ahead of the spectracom phase detectors Detect the phase shift and through a simple microproc and very simple code flip the incoming signal in about 2-5 cycles of 60 Khz. (This could also be done in simple logic.) The value of the proc is it lets me easily tinker with the decision to flip or not. Noise and lock out ignore etc. But its dependent on the likes of a spectracom 8163 kindly given to me from another time-nut for the cost of shipping. So its not a general purpose solution. Given the new information released a few days ago by NIST there are several more possibilities that essentially look at the top of the minute. Gather the phase of a local non locked source slightly adjust it per minute and then through the minute at every 1 sec + 100 ms check the phase and flip teh path.(Long fades are still a issue) This approach actually re-establishes a 0 phase coherent solution and though its a pll its a really loose pll without the need for various filters and feed back. Its a feed forward approach. An interesting item of note in a bandwidth limited channel such as used in most of these rcvrs that have a xtal filter. The phase flip also causes a 0 carrier (Or hugely reduced)for a small amount of time. May be useful. I am actually looking for the next test to see if the approach really does work as written here. I have had enough false starts, used lots of opamps, and solder over the last 6 months. Regards Paul WB8TSL On Thu, Sep 27, 2012 at 9:34 AM, Attila Kinali <att...@kinali.ch> wrote: > Moin, > > On Thu, 27 Sep 2012 08:53:03 -0400 > paul swed <paulsw...@gmail.com> wrote: > > > I am feeling a bit slow here. > > There is a carrier always. Thats how the AM works. So somehow we are > > speaking about a semi non coherent carrier perhaps?? > > So whats the nickle solution and it is not squaring in a low s/n > > environment. Been there done that. Very bad results on the east coast. > > Regards > > Yes, there is still a carrier left. A BPSK spektrum looks like a > sin(x)/x signal which is centered on the carrier. Yes, you can > sync on this signal without much difficult... if you use the right method. > And that's where the problem lies. Most old devices use a PLL to sync > to the signal, which tracks the phase. Now if the phase jumps 180° > every second, the PLL will jump back and forth every second (or actually > on every 0-1 and 1-0 transition). Ie you have a jump of the PLL error > signal every second, possibly unlocking the PLL until the PLL has locked > in again. This jumping will disturb any frequency normal. > > A way to mitigate this problem is to use > 1) a smaller phase step than 180° > 2) a higher modulation frequency > 3) a modulation that has an average of 0, even on the short term > (as in shorter than the time constant of a "standard" PLL) > > 1) and 2) allows the PLL filters to filter out the phase steps and 3) > ensures > that the modulation pattern doesnt change the frequency, even in the short > term. > > If you find yourself reminded of something... Yes, this is exactly what > DCF77 has done for over 20 years....[1] > > I really wonder why they didn't copy the modulation scheme of DCF77 for > WWVB or at least take ideas from it... > > Attila Kinali > > [1] http://remco.tk/handig/DCFp.pdf > > -- > It is upon moral qualities that a society is ultimately founded. All > the prosperity and technological sophistication in the world is of no > use without that foundation. > -- Miss Matheson, The Diamond Age, Neil Stephenson > > _______________________________________________ > 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.
