My understanding has always been that you need 4+ satellites to get an initial timing lock, but then, so long as you keep at least one, you’ll keep that timing lock.
From: Af [mailto:af-boun...@afmug.com] On Behalf Of Bill Prince Sent: Tuesday, August 11, 2015 2:08 PM To: af@afmug.com Subject: Re: [AFMUG] GPS Timing That's what I thought too. Once one of these little beggars has been online for a half hour or more, the location should be "set" so to speak. I would then expect them to hold time sync even with 1 satellite in view. Knowing that the location is static and unmoving, I would expect that maintaining time lock would be gravy. Sadly, this does not seem to be the case. bp <part15sbs{at}gmail{dot}com> On 8/11/2015 10:48 AM, Chuck McCown 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) <mailto:li...@packetflux.com> Sent: Tuesday, August 11, 2015 11:39 AM To: af <mailto:af@afmug.com> 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" <d...@wyoming.com> 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.)?
