knowing where you are also involves knowing when you are ;-)
On Tue, Aug 11, 2015 at 11:48 AM, Chuck McCown <[email protected]> wrote: > Interesting, I guess you need to know where you are to calculate the > delay. Had not considered that. But if you know where you are and have > ephermis data, you should be able to calculate the delay and arrive at a > pretty accurate timing pulse with one satellite. > > *From:* Forrest Christian (List Account) <[email protected]> > *Sent:* Tuesday, August 11, 2015 11:39 AM > *To:* af <[email protected]> > *Subject:* Re: [AFMUG] GPS Timing > > > You need an accurate 3d position to get accurate timing. To have an > accurate 3d position using GPS alone, you need four satellites. Three > only gets you a 2d lock, and less than that you don't get a lock at all. > > There are receivers out there which will survey a position and then use > that position to be able to continue to provide a timing signal if you > subsequently lose lock but still have sats in view. As far as I know, > this type of receiver is not in use in any commercially available timing > product for the cambium radios. In fact I think we've almost all ended up > using the exact same GPS modules, at least for any recently designed > product. > > Some of the earlier products would attempt to preserve the sync signal > across a GPS lock loss with various levels of success. For instance the > cmm micro in early releases provided a wildly incorrect sync pulse even > without a lock. Same with early syncpipes. The CTM has a holdover > timer. And so on. I think most of us have moved away from this in newer > designs. > On Aug 11, 2015 8:36 AM, "Dan Petermann" <[email protected]> wrote: > >> What is the minimum amount of satellites needed for a proper GPS sync >> pulse? >> >> And does that differ across products (CMM, CTM, SyncPipe, etc.)? >> >
