Hi Commonly this sort of thing is done with a sample and hold in the loop. No reference in / put the loop voltage in hold. You still have a phase drift and need to cope with the phase offset when the reference comes back.
Bob On Sep 19, 2012, at 4:08 AM, Azelio Boriani <azelio.bori...@screen.it> wrote: > In my opinion you fall in the case of disciplining with holdover... this is > more like a disciplined oscillator (like a GPSDO) problem than a PLL. > > On Wed, Sep 19, 2012 at 1:45 AM, Jim Lux <jim...@earthlink.net> wrote: > >> On 9/18/12 9:48 AM, Raj wrote: >> >>> If you break the DC control chain of the PLL with a A2D and a controller >>> and back with a D2A .. you would program the control with any kind of >>> behavior you want. Just a thought! >>> >>> That is exactly what we do... the PLL is actually implemented digitally >> (DAC driving the VCO).. >> >> But what I'm looking for is a theoretical treatment of the output >> statistics (Allan Dev, mostly) in terms of the interrupted reference input. >> >> For context.. we do precision ranging of spacecraft in deep space by >> sending a hydrogen maser derived signal TO the spacecraft which locks a >> local VCXO to that signal, and then uses the VCXO to generate a return >> signal with a constant ratio (e.g. 880/741) to the input. >> >> By measuring the time it takes for the round trip (essentially counting >> phase cycles on the return signal (against our hydrogen maser, again), we >> measure Range and Doppler, which is then used to determine the position of >> the spacecraft. >> >> Typical performance is sub-meter and sub cm/sec. (A very high performance >> would be that the transponder adds 4E-15 Allan Dev over 1000 sec... 1E-11 >> or 1E-12 over 10-100 secs is more usual) >> >> What we want to know is "what happens if the receiver and transmitter >> can't run at the same time"? Obviously, we have less information coming >> into the system (we see the uplink half the time, so right there, we have a >> 2:1 hit) and the ground end only sees the transmit signal half the time >> (another 2:1 hit), so, from an information theory standpoint we've already >> put ourselves in a hole, but, what does the statistics really look like for >> the turnaround loop.. >> >> Full Duplex full power turnaround is expensive in power, mass, etc. (for >> instance, you have to have good filters to make sure that your receiver >> isn't corrupted by the transmitter) >> >> >> >> >> ______________________________**_________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/** >> mailman/listinfo/time-nuts<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. _______________________________________________ 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.