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] <mailto:[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] <mailto:[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] <mailto:[email protected]> |
http://www.packetflux.com
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