[time-nuts] GPSDO Component Selection

bg at lysator.liu.se bg at lysator.liu.se
Sun Sep 9 23:25:20 UTC 2012


Hi Bob,

Probably true for Motorola Oncores. Not very true for geodetic receivers.

Until you have a receiver clock that is on par with the satellite clocks
AND you are short on visable satellites. This might be true if you can
load up a modern cesium in your vehicle, and go for a downtown "urban
valley" type of scenario.

On a stationary site, your expensive clock will not matter to much, since
your solution is already pretty over-determined with some 60 measurements
on each epoch. (9 GPS +6 Glonass)*2(L1/L2)*2 (code + phase)

--
    Björn

> Hi
>
> Position accuracy and timing accuracy are two very different things.
> Firmware is optimized to improve either one. "Position" firmware is often
> pretty poor for timing.
>
> Bob
>
> On Sep 9, 2012, at 5:05 PM, Chris Albertson <albertson.chris at gmail.com>
> wrote:
>
>> On Sun, Sep 9, 2012 at 1:14 PM,  <bg at lysator.liu.se> wrote:
>>
>>> True for a cheap oem navigation receiver. Not true for a geodetic
>>> quality
>>> receiver, who usually have some options (external frequency input,
>>> PPS_in)
>>> to make them the best timing receivers available. However they are much
>>> more expensive than the typical single frequency timing reciver.
>>
>> I looked at every link and can't see where they give a timing accuracy
>> spec on the PPS with respect to UTC.   Possition accurracy is very
>> good and we might assume the timing is as good.  But they don't say it
>> is.  What's interesting is these GPSes will accept an accurate clock
>> input in order to give better location data.   That is the opposite of
>> a timing GPS where you tell it accurate location data so that it can
>> get better timing.   Cutting down the unknown in one lets you do
>> better in the other.   I assume these all cost well over $50.  You can
>> get a pretty good timing GPS for $30 and it WILL have the PPS error
>> specified.
>>
>> To the OP.  None of this matters a lot because PPS is a standard input
>> signal.  It is easy to swap out a GPS receiver later.  Same with the
>> OCXO.  From a control point of view they are all pretty much the same.
>> You can swap them out later
>>
>>
>> Chris Albertson
>> Redondo Beach, California
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>






More information about the Time-nuts_lists.febo.com mailing list