Hi Neville, There are plenty of ways to compare frequencies.
I posted the BPSK demod scheme as a simple way to quickly tweek in the correct direction without Lissajous Figures. Best, -John ================ > > There is another way to compare two frequencies, relevant when they > are very close together. > I divide a reference down to 100KHz and use it to clock a phase > detector made of a pair of D flip flops. > The unknown (divided to 100KHz) is fed into the circuit and an output > that is proportional to the phase > difference appears on the output as a changing mark-space ratio. > Using CMOS and a precise power supply (because under no load, CMOS > output is precisely rail to rail), > the averaged output (100ms RC filter) is fed to a strip chart > recorder. > The recorder shows the changing phase difference and folds back each > time a whole cycle passes. > A 12 bit analog data logger resolves 2.5ns of phase and gives data > for further analysis. > There may be a small amount of missing data in the vicinity of the > foldback, but if life threatening this could be avoided > by running a second unit with the signals delayed to be near > quadrature, and using the better data of the two. > I use a lower frequency version of this system to monitor clocks > (mechanical ones with pendulums). > Cheers, Neville Michie > > _______________________________________________ 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.
