+1 relativity
Josh Luthman
Office: 937-552-2340
Direct: 937-552-2343
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On Tue, Aug 11, 2015 at 2:47 PM, Sean Heskett <af...@zirkel.us> wrote:
> It's all relative man
>
>
>
> On Tuesday, August 11, 2015, Bill Prince <part15...@gmail.com> wrote:
>
>> Actually, everything is orbiting the sun at about the same speed, but
>> we're digressing...
>>
>> bp
>> <part15sbs{at}gmail{dot}com>
>>
>>
>> On 8/11/2015 11:25 AM, Sean Heskett 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 <part15...@gmail.com>
>> 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)
>>> *Sent:* Tuesday, August 11, 2015 11:39 AM
>>> *To:* af
>>> *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.)?
>>>>
>>>
>>>
>>
>>
