We don't need any stinkin' commie RF!
Добрий День товарищ!
On Wed, Aug 12, 2015 at 12:36 PM, Shayne Lebrun <[email protected]
<mailto:[email protected]>> wrote:
Nyet, Tovarich. Superior SOVIET RF works four times as hard as
any lazy capitalist RF, and without exploiting the proletariat
photons.
*From:*Af [mailto:[email protected]
<mailto:[email protected]>] *On Behalf Of *Jaime Solorza
*Sent:* Wednesday, August 12, 2015 1:22 PM
*To:* Animal Farm
*Subject:* Re: [AFMUG] GPS Timing
not to worry Comrade RF is universal
Jaime Solorza
Wireless Systems Architect
915-861-1390 <tel:915-861-1390>
On Wed, Aug 12, 2015 at 9:52 AM, George Skorup <[email protected]
<mailto:[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] <mailto:[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]> 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)
<mailto:[email protected]>
*Sent:*Tuesday, August 11, 2015 11:39 AM
*To:*af <mailto:[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 <tel:406-449-3345> | Address: 3577
Countryside Road, Helena, MT 59602
[email protected] | http://www.packetflux.com
<http://www.linkedin.com/in/fwchristian>
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