David Yes I have seen various comments and documents describing MSK that way. But have to say the tracor 900 does not use that method to establish a reference. Its a few opamps perhaps one side acting as a phase delay summing with the original and hitting a BPF. all of that running at 100Hz center frequency. Through this magic the 900 could use NAA as a phase tracking reference. Its as if its a classic phase doubler. The documentation almost speaks to that. Its seriously simple. Regards Paul. WB8TSL
On Fri, Aug 15, 2014 at 4:31 PM, David I. Emery <[email protected]> wrote: > On Fri, Aug 15, 2014 at 03:09:23PM -0400, paul swed wrote: > > > I had discounted it because of the lack of info and totally unclear how > to > > get rid of the FSK. MSK is FSK just with a very narrow shift. Also the > > effects of the fsk on the carrier. Hmmm glad I am typing this. > > It may be that the mark or the space is indeed exactly the true carrier > and > > that op amp circuit is notching out the shifted carrier. I will bet thats > > the trick! > > > MSK is a kind of continuous phase differentially coded PSK in > which the carrier phase smoothly shifts either EXACTLY plus 90 degrees > or EXACTLY minus 90 degrees in EXACTLY one symbol time - in the MSK > variety of PSK the transmitted carrier phase never stays the same as the > it was the last symbol time. When transmitting steady mark there are a > series of these shifts plus 90 degrees (hi frequency mark) one after the > other, and when transmitting steady space there is a series of minus 90 > degree shifts. > > Obviously a steady negative phase shift is what is produced by > a signal below a center "carrier" frequency and a steady positive > phase shift by one above that frequency. Thus the isomorphism with > filtered FSK. > > Effectively a QPSK (multi-arm Costas type) tracking loop should > be able to track a MSK signal just as if it was a filtered QPSK signal > with only 90 degree and minus 90 phase shifts each symbol time and generate > a phase continuous recovered carrier. > > > > > > -- > Dave Emery N1PRE/AE, [email protected] DIE Consulting, Weston, > Mass 02493 > "An empty zombie mind with a forlorn barely readable weatherbeaten > 'For Rent' sign still vainly flapping outside on the weed encrusted pole - > in > celebration of what could have been, but wasn't and is not to be now > either." > > _______________________________________________ > 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.
