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

Chris Albertson albertson.chris at gmail.com
Thu Mar 1 23:11:22 UTC 2012


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.

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?

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.


-- 

Chris Albertson
Redondo Beach, California


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