[time-nuts] Time Transfer

[Brooke Clarke]

Hi Didier:

If you have a high elevation mask, as I do to avoid most of the tree tops, then 
it's a common occurrence that there's only one SV in view.  But in position 
hold mode the receiver can compute the time and the 1 PPS output is good.

I'm not sure how the receiver combines all the SVs that it's tracking, but all 
that are being tracked are part of the solution.

The more accurate the position used to lock the receiver the better the 
results.  It's about 1 ns per foot in air.  I hired the local surveyor who does 
GPS to locate my antenna and a few spots around the house that are on even 
second Lat and lon numbers, like 39:11:25.00000.

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.precisionclock.com
http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Cam


Didier Juges wrote:
> Hi Brooke,
> 
> Thank you for your suggestions, that page is probably ripe for a rewrite,
> but I may just add a link to your page for now :-)
> 
> I would have thought the GPS receiver averages the readings when it locks on
> multiple satellites. Are you saying it only uses one at a time? If so,
> what's the point of a self survey?
> 
> I talk about WWV because most ham operators have a receiver that receives
> WWV, so it is an inexpensive and convenient way to get an absolute
> reference, even though it is not as good as GPS.
> 
> I am sure there is a reason why timing receivers track all the way down,
> instead of switching to a better bird when one is available, but by setting
> the mask angle fairly high (appropriate for your location and obstructions),
> you can take care of this problem.
> 
> Didier KO4BB
> 
> 
>>-----Original Message-----
>>From: time-nuts-bounces at febo.com 
>>[mailto:time-nuts-bounces at febo.com] On Behalf Of Brooke Clarke
>>Sent: Friday, December 14, 2007 2:16 PM
>>To: time-nuts at febo.com
>>Subject: [time-nuts] Time Transfer
>>
>>Hi Didier:
>>
>>Been surfing your Timing web page and came across 
>>http://www.ko4bb.com/Timing/FrequencyReference.html
>>Got there by working up the URL for the Vig paper.
>>
>>An ordered list of Time Transfer methods from carrier phase 
>>GPS to the Astrolabe is at:  http://www.prc68.com/I/timefreq.shtml#TT
>>that ranks HF time stations far below other methods, so 
>>although they can be used there may be better choices that 
>>are affordable.
>>
>>Also for GPS timing applications (i.e. the GPS receiver is in 
>>position hold
>>mode) a single satellite is all that's needed.  Adding more 
>>satellites can add a failure alarm function but may not 
>>improve accuracy.  In my case multipath is a big problem so a 
>>high elevation mask is needed.
>>
>>The problem with a less than 12 channel receiver relates to 
>>how satellites are selected.  The Motorola timing receivers 
>>will continue to track a satellite until it sets rather than 
>>switch to a a new one which may be directly overhead. 
>>  The "use highest in the sky" applies to how a new satellite 
>>is selected. 
>>Once selected the satellite is tracked until it sets.
>>
>>An idea: When averaging GPS 1 PPS signals the receiver 
>>switches satellites as the currently tracked ones set so 
>>there may be a slight change in accuracy because of the 
>>satellites being used.  But changing from a satellite that's 
>>about to set i.e. that has a lot of multipath to high in the 
>>sky sat should make for a better 1 PPS.
>>
>>-- 
>>Have Fun,
>>
>>Brooke Clarke
>>http://www.PRC68.com
>>http://www.precisionclock.com
>>http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Cam
>>
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> 
> 
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