> -----Original Message----- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On > Behalf Of Bruce Griffiths > Sent: Wednesday, February 17, 2010 2:27 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] DMTD to MMTD > > Lux, Jim (337C) wrote: > >> -----Original Message----- > >> From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On > >> Behalf Of Bob Camp > >> Sent: Wednesday, February 17, 2010 1:57 PM > >> To: 'Discussion of precise time and frequency measurement' > >> Subject: Re: [time-nuts] DMTD to MMTD > >> > >> Hi > >> > >> Thanks for the quick response. > >> > >> The impression I've always had of that system is that it is comparing the > >> sources two at a time. They can select between a number of sources, but > >> only > >> one pair is looked at. > >> > >> > > It basically timestamps transitions on all 8 inputs. The post processing > > software that looks a the > timestamps is what selects either 1 channel (single mixer+offset generator) > or 2 channels (dual mixer > time difference) > > > > The counters in the FPGA are running at 100 MHz, so they have a basic > > resolution of 10 ns. > > > > _______________________________________________ > > > See: > > http://tycho.usno.navy.mil/ptti/ptti2006/paper11.pdf > >
That's basically the same as the IPN progress report you linked in the earlier email. Same figures, nicer typography, but the figures are better in the IPN progress report (169B). As it says, referring to the Counter Assembly: "It latches the readings of a continuously-running 100 MHz counter at the zero-crossing times of all channels that have a valid signal present. The output is fed continuously into the computer's serial port with no flow control." Steve Cole doesn't show up in the phonebook, so I can't just call him for more details, but I could probably find a copy of the footnoted description. I'd actually be more interested in the design of the zero crosser. Seeing if one could get a copy of NPO-40468 from NASA Tech Briefs (if it was published there) might also be useful. Try this: http://www.techbriefs.com/component/content/738?task=view Or http://www.techbriefs.com/component/docman/doc_download/2222-progress-on-a-multichannel-dual-mixer-stability-analyzer those reference http://www.techbriefs.com/component/content/article/7326 http://www.techbriefs.com/component/docman/doc_download/1618-oscillator-stability-analyzer-based-on-a-time-tag-counter but there's nothing much new in that one.. _______________________________________________ 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.
