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 Paul WB8TSL
On Thu, Sep 27, 2012 at 1:15 AM, Peter Monta <[email protected]> wrote: > > I'm not sure about residual carrier aiding the tracking process. A > Costas > > loop recovers the carrier pretty well, and a symbol aided loop (where > the I > > channel has a hard limiter, for instance) does even better. > > Yes, these work (and a soft tanh() limiter improves on the hard > limiter a little bit), but I think they don't work as well as a PLL > with a pure carrier, where performance is measured as the variance of > the phase estimate at a given SNR. > > > After all, the energy is still the same. > > True, but information has been lost as a result of introducing these > unknown phase transitions. Now if the phase transitions are known, > one can certainly wipe them off by multiplying by a noiseless replica > of the known phase modulation, and then you're back to pure carrier. > But if you don't know the transitions ahead of time, you need the > Costas loop to find them for you, and that costs SNR. > > In WWVB's case, many of these phase transitions probably can be > predicted. But the point is not so much that good timing receivers > for the new signal are problematic. On the contrary, they're no > problem at all with a little DSP. But for the sake of backward > compatibility, putting 5 or 10 percent of the signal power into a > carrier seems a small price to pay. > > Using a Costas-loop preprocessor to a legacy phase receiver is almost > to the point where you're better off tossing the legacy receiver and > just using the preprocessor. > > I don't want to sound too negative here. I'm glad WWVB is getting > these improvements, and the clarification from John Lowe earlier today > about the openness of the signal is helpful. But backward > compatibility would have been so easy to put in. > > Cheers, > Peter > > _______________________________________________ > 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.
