[time-nuts] Motion effects on accuracy of GPS pps

Daniel Davson ddavson at peralex.com
Wed Jun 30 03:41:41 EDT 2010


Thanks Didier,

There's also some useful information on the subject here: 
http://www.greenrayindustries.com/accsens_tb3.html

Regards,
Dan

Didier Juges wrote:
> From memory, I believe tvb did some experiments with an OCXO or Rb measuring AVAR while flipping the oscillator upside down (+/- 1g). You may find links on tvb's web site www.leapsecond.com
>
> At the moment, I cannot find the link...
>
> Didier
>
> PS: Note to tvb: Tom, when you have time, a search or indexing feature on your web site would be very useful. Apparently, Google is not able to find much of the excellent resources and data you have, maybe because many pages are not linked through the main page?
>
> ------------------------ Sent from my BlackBerry Wireless thingy while I do other things... 
>
> -----Original Message-----
> From: Daniel Davson <ddavson at peralex.com>
> Sender: time-nuts-bounces at febo.com
> Date: Tue, 29 Jun 2010 15:11:19 
> To: Discussion of precise time and frequency measurement<time-nuts at febo.com>
> Reply-To: Discussion of precise time and frequency measurement
> 	<time-nuts at febo.com>
> Subject: Re: [time-nuts] Motion effects on accuracy of GPS pps
>
> Thanks for the response Björn. Also thanks to Didier Juges for pointing 
> out that this has been covered on a previous thread. I'll go and find it 
> in the history.
>
> Unfortunately the device will be used in urban areas so some multipath & 
> obstruction of skyview is expected. I've just done some testing on my 
> OCXO and it has a maximum sensitivity of about 5 ppb / *g*, which is 
> notable, but shouldn't present a problem. I've yet to explore the 
> vibration effects - thanks for pointing my attention to the motion 
> effects on the OCXO itself, its an aspect I'd otherwise have overlooked.
>
> Daniel
>
> bg at lysator.liu.se wrote:
>   
>> > Hi Daniel,
>> >
>> >   
>>     
>>> >> Hi,
>>> >>
>>> >> I've recently completed a GPSDO using the pps output of a uBlox Antaris
>>> >> TIM4 GPS module to discipline a 10MHz OCXO. I'm now investigating the
>>> >> motion effects (acceleration/uniform velocity) on the accuracy of the
>>> >> time-pulse and hence on my frequency output.
>>> >>     
>>>       
>> >
>> > Are you moving around in areas with little obstruction for the GPS antenna
>> > towards the sky? Then I would first look at the dynamics inpact on your
>> > OCXO.
>> >
>> >   
>>     
>>> >> I've been unable to find any detailed information on the relationship
>>> >> between the accuracy of the pps output and the effects of having the
>>> >> receiver in motion (i.e. in a car/boat, at velocities far below the
>>> >> modules operating limit of 515m/s) - I'd appreciate some input on this
>>> >> matter. Does motion cause increased jitter?
>>> >>     
>>>       
>> >
>> > Tilting/accelerating your GPS oscillator might possibly yield an effect.
>> > Other than that there is no theoretical advantage keeping your receiver
>> > stationary. All its measurements are done against satellites moving at ca
>> > 4km/s.
>> >
>> >   
>>     


-- 
Daniel Davson
HW Design Engineer
Peralex Electronics (pty) ltd.
Peralex House, 5 Dreyersdal Rd, 
Bergvliet 7945, South Africa
Tel: +27 21 710 7446


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