[ntp:questions] how do you like the Trimble Resolution T

unruh unruh at invalid.ca
Fri Mar 2 00:27:34 UTC 2012


On 2012-03-01, Chris Albertson <albertson.chris at gmail.com> wrote:
> On Wed, Feb 29, 2012 at 11:59 PM, unruh <unruh at invalid.ca> wrote:
>>
>>> Whilst the Oncore UT+ which Chris mentions may have better ultimate
>>> performance, I don't think you will see the difference in an NTP
>>> application on the great majority of PCs.  It doesn't come with an
>>
>> .... Persuading a PC to respond to the interrupt in under 1us would
>> be pretty good work (mine are more like 2-20us response time)
>>
>>> antenna, tracks only 8 channels (at least that's one I found on eBay), and
>>> also requires a connection lead to be assembled.  Looks nice, though!
>
> One could argue the UT+ is "over kill" for an NTP server.  It might be
> but it's also half the cost of the next option.   So what the heck,
> better performance than you can use at half the cost.

Not with an antenna it is not half the price. 

>
> What OS are you running?   2-20us response time is not great unless
> you mostly get 2 us.   It sounds like you might have some device driver
> that runs with interrupts disabled.   Maybe you can figure out which
> it is?
Linux. Mostly it is about 2-3us standard deviation (as seen from the
scatter of the offsets)  and very occasionally
( when the sysem is using its disk drive a lot) it can go up to 20. 
>
> It might seem odd that a 10 year old GPS that only 8 channels gives
> better performance than most new 12 channel units but such is the
> difference between a timing GPS and a general purpose unit.  New
> timing GPSes have 1 sigma errors in the 5 ns range and cost about $60.
>
> The tracking number really is not important.  All GPS receivers
> download the entire almanac and can figure out where all satellites
> are, even those that are below the horizon.  Then it figures out which
> set are going to give the best data and listens to those.
>
> A timing GPS will continue to operate with only 1 sat in view.  The
> general purpose navigation GPS is going to need four in view to makes
> it's 3D solutions.
>
>



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