[ale] semi [OT] NTP questions - and NTP Windows - was: possibility of running an NTP server

[Michael H. Warfield]

On Sat, 2012-01-14 at 01:38 -0500, mike at trausch.us wrote: 
> On 01/13/2012 04:54 PM, Ron Frazier wrote:
> > NTP is polling the NIST service every 4 minutes, and, as you can see 
> > from the red graph, my clock offset is all over the place, varying from 
> > -5 ms to +110 ms.  I also notice that the frequency is drifting up from 
> > -13 to -9.  Can someone explain to me in a few words what the frequency 
> > means?  Does this graph mean that the system is trimming my clock?

> It is more than sufficient to set your clock once a day.  Much more
> frequently than that and it is considered impolite.

> Even the most horrible of PC clocks I have encountered don't drift more
> than 10 seconds per day.  The average, IME, is 0.5 to 4 seconds per day.
>  If you need to get more accurate than that, then purchase or build a
> WWVB receiver that can feed your computer the current time directly from
> the radio signal.  Then you can have your computer constantly up-to-date
> when the signal is coming in, and you shouldn't drift horribly when it
> isn't.

Honestly, in this day and age of cheap GPS receivers, a better option is
to hook up a serial port or USB GPS receiver and set up your very own
personal stratum 1 time server.  The NTP package has support for the
standard GPS protocols like the various NMEA protocols and extensions.

You can pick up a Delorme LTE-40 USB connected GPS that will talk the
NMEA protocols for under $50, including their map package (you'd have to
call for a price on just the receiver).  This thing is even WAAS enabled
so it can pick up the differential signals from the geosynchronous WAAS
sats.

http://shop.delorme.com/OA_HTML/DELibeCCtdItemDetail.jsp?item=31129&section=10091

If you like construction projects, you can pick up different GPS
packages to build into a project yourself.  I've seen some OEM modules
that are specifically designed for high accuracy time reception (you get
them optimize them for 2D location, 3D location, time, and a few other
parameters).

http://www.futurlec.com/GPS.shtml

All you need is some decent spot for signal reception but modern chips
are amazing.  The GPS in my EVO 4G works in the middle of my basement,
albeit with low signal strength but still, it works...  Near a window
would do the job.  Or you can get some pretty cheap active antennas that
are waterproof and suitable for outdoor mounting...

Much easier and every bit as accurate as setting up a WWVB receiver.
Probably a lot cheaper two, although I haven't priced out a receiver in
a lllooonnnggg time.

> 	--- Mike

Mike
-- 
Michael H. Warfield (AI4NB) | (770) 985-6132 |  mhw at WittsEnd.com
   /\/\|=mhw=|\/\/          | (678) 463-0932 |  http://www.wittsend.com/mhw/
   NIC whois: MHW9          | An optimist believes we live in the best of all
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