You cannot put a narrow filter before the squarer for reasons previously cited. In a low S/N area, squaring just makes matters worse wrt dynamic range and clipping.
-John ========== > Hi > > A PLL locks to phase. If the phase switches by 180 degrees, the phase > tracking switches signs. There's no way to track that. You either need to > double the frequency (and thus eliminate the modulation) or demodulate the > signal and lock to the result. If you simply put up a real narrow filter > and hit it with continuous 180 degree phase shifts, the output will be > nothing at allÂ… > > Bob > > > On Sep 27, 2012, at 7:11 PM, [email protected] wrote: > >> Various comments - >> >> Hal mentioned SNR for the scheme I suggested. A PLL can be a coherent >> demodulator of arbitrary >> bandwidth. Thus the PLL at the output of the doubler can have a small >> bandwidth since at that point >> there is no PSK, it having been removed by the doubler. So given a >> stable VCXO you can probably get down >> to 1 Hz and thereby achieve a good SNR. There is a lot of stuff out >> there on phase tracking receivers >> that do exactly that. You know the frequency so the loop does not have >> to search far and the BW can be increased >> for acquisition and closed up for tracking. >> >> On writing reams of code - my point was that it is not required to used >> the admittedly more powerful software >> techniques to do this job - I noted that one reason to write reams of >> code is for the fun of it, this is after all >> a hobby. >> >> GPS Antenna Siting - >> >> Lets not make this so hard. Mine is at 6 ft elevation and is blocked to >> an elevation angle of 20 to 30 degrees by a house >> within 15 ft and a forest of trees. I have room and no restrictions but >> I also have severe thunderstorms - so the house >> plays lightning protect for the antenna. My T bolt tracks a Rb to better >> than 1e-12 over 24 hours with no serious 10 MHz phase bumps >> as plotted on a strip chart recorder. >> >> Sooooo - >> >> Put your antenna at 6 ft in back yard. Start out on a photo tripod - who >> is gonna notice? >> set up a t bolt at EL=5 AMU=0 Damping = 1.2 and Time Constant = 100 sec. >> get the t bolt manual >> get Tbolt monitor >> get Lady Heather and read all that stuff. >> >> Run Lady Heather antenna survey (command SAS) for at least two days - >> you get a map of signal level in dBc vs elevation >> Reset the Tbolt elevation mask to reject anything that is shown as >> blocked using the signal >> level map. Likewise experiment with the AMU setting to reject the weak = >> poor signals. Mine works good >> with AMU all the way up to 10 as fewer good satellites are better than >> lots of weak ones. >> >> The satellites are in high orbits so masking those below 25 degrees is >> OK and the AMU sets the acceptable signal >> level - at AMU 10 my setup throws out those below about 40 dBc - the >> strong guys go up to 50. This is a function >> of you antenna performance so some experimentation is required. >> >> -73 john k6iql >> >> >> >> >> _______________________________________________ >> 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.
