Interesting... this explains why they use a 20MHz OCXO (without EFC) in the FTS125 to clock the receiver that has an NCO steered that clocks a PLL that synchronize another OCXO (with EFC). Yes, I have opened up an FTS125.
On Wed, Jan 4, 2012 at 8:32 PM, Ed Palmer <ed_pal...@sasktel.net> wrote: > On 1/4/2012 11:13 AM, Said Jackson wrote: > >> Hi Ed, >> >> Since the oscillator is typically free-running in an NCO, and >> periodically corrected by phase drops to stay "on frequency" the error you >> are seeing may be caused be the offset in your crystal, combined with the >> limited digital resolution of the NCO trying to correct for this offset. >> >> If this is the case, your measured error would change with temperature. >> >> Does it do that? >> > > Yes, it does. Cooling the unit by using a heatsink causes a significant > increase in the output frequency. The change is large enough to be obvious > on an oscilloscope where one channel is the 10 MHz from the Z3801A and the > other channel is the 10 MHz from the CW12. > > > If yes, the NCO resolution is not fractionally corrected all the way. >> Replacing the on board Tcxo with an ocxo hand-tuned to the correct >> frequency would help, but that sort of defeats the purpose of the product.. >> > > Yes, it appears that the CW12 is just not appropriate for what I was > thinking of doing. However, to be fair, the 1 PPS output is much better > than the older receivers. I'll have to think about where I go from here. > > > Ed > > > _______________________________________________ > 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.