not to worry Comrade RF is universal Jaime Solorza Wireless Systems Architect 915-861-1390
On Wed, Aug 12, 2015 at 9:52 AM, George Skorup <[email protected]> wrote: > Cambium is using a new receiver on the 450APs that does GPS+GLONASS. I > assume it's from Global-Top, but I haven't opened up a new AP to look. I'm > not real excited about using the Russian signals, but with so many > satellites available, it does acquire lock very fast. Have you thought > about doing the same for your 'Pipes? I think it would be beneficial. > > > On 8/12/2015 5:34 AM, Forrest Christian (List Account) wrote: > > Ok, if you really want to know, I finally found a (somewhat data) document > which describes this in semi-understandable terms. > > And yes, the real time does fall out of the equations (see watch error - > which is how fast or slow your reference clock is). > > http://www.maa.org/sites/default/files/pdf/cms_upload/Thompson07734.pdf > > What I'm hearing from my GPS module vendor is effectively that since they > don't really have to do any additional work to output a 1PPS signal from a > 3d lock, they feel comfortable in doing so. Adding the complexity of > surveying an location to an useful accuracy and then using that to compute > the time is a lot of additional work with a lot of variability they don't > want to try to deal with without additional demand. I do know that a > while back we tried some shortcuts to get there, but they were not all that > useful. > > -forrest > > On Tue, Aug 11, 2015 at 12:25 PM, Sean Heskett <[email protected]> wrote: > >> the satellites are constantly moving tho and since they are moving faster >> in orbit than we are here on earth you need to account for relativity. >> knowing where you are doesn't give you enough information to know where >> the satellite is and therefore you can't accurately calculate the >> relativity offset. once you have 3D lock with 4 satellites you can >> accurately calculate the relativity offset and therefore calculate the >> accurate time for where you are on earth. >> >> shoulda taken the blue pill ;-) >> >> -Sean >> >> On Tue, Aug 11, 2015 at 12:08 PM, Bill Prince < <[email protected]> >> [email protected]> wrote: >> >>> 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) <[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.)? >>>> >>> >>> >> > > > -- > *Forrest Christian* *CEO**, PacketFlux Technologies, Inc.* > Tel: 406-449-3345 | Address: 3577 Countryside Road, Helena, MT 59602 > <[email protected]>[email protected] | <http://www.packetflux.com/> > http://www.packetflux.com > <http://www.linkedin.com/in/fwchristian> <http://facebook.com/packetflux> > <http://twitter.com/@packetflux> > > >
