Why make it simple when complicated also works? -John
============ > On 3/15/12 7:49 AM, J. Forster wrote: >> Suppose the modulation is not present. The output of the phase detector >> that steers the local standard ot indicator works correctly. >> >> Now reverse the 60 kHz carrier. The phase detector works exactly thye >> opposite way... wrong. >> >> Now alternate between 0 and 190 degrees. >> >> The loop alternate works between exactly right and exactly wrong... it >> dithers around and the output is a measure of the ratio of 1's to 0's >> and >> is utterly useless. >> > > and the cleverness of the Costas loop is that it uses (an estimate of) > the current data bit (the output of the I arm) to flip the sign of the > error signal from the quadrature arm. > > There's a lot of scope for modification of the basic linear Costas loop. > Hard/soft limiters in either or both arms, you've got three filters > (the two arm filters and the loop filter) to fool with, plus all sorts > of schemes using "data aiding" where you get feedback from your symbol > slicer to help do a better job on the carrier tracking. > > You can also run your loop with hard limited signal input (makes the > "mixers" turn into XOR gates). > > If you don't need the bits in real time (i.e. you can tolerate some > latency), then you can also build tracking loops that effectively "look > into the future"; i.e. make decisions on carrier and bit at time t using > future data from t>now, as well as t=[-infinity, now]. > > > Enormous literature out there on this, and it's been grist for many a > Master's or PhD dissertation. > All in a quest to get ever closer to the Shannon limit... > > _______________________________________________ > 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.
