[time-nuts] PC Time Servers

[David J Taylor]

Richard,

Faros uses a precise time of day to determine the time it took for the 
beacon signal to reach your location.  It uses this info to determine if the 
path was the short path, or the long path.

The NCDXF beacons use a GPS receiver to determine a very accurate time of 
day, and to start their transmission at a precise time.  Faros looks at the 
clock time when it hears the signal arriving at the receiver it’s listening 
with. It knows the exact location of the transmitter and your exact 
location.  Form there, it can calculate the spherical distance, both the 
“short path” and the “long path”.  With the distance known, and the delay in 
receiving the signal, Faros can then determine if the signal arrived at your 
location via the short path, or the long path (or both!).

Faros gets the correct time of day, by using it’s own built in NTP.  It has 
a list of NTP servers, and it uses the NTP algorithm to determine the 
 “delay” to that server.  Faros ranks the quality of the NTP servers by 
delay.

An interesting experiment is to tell Faros a location that’s much different 
than where it’s receive really is located.

KR
================================

Kevin,

>From that I would expect the receiver & PC to have a good sub-millisecond 
accuracy, and the best way to achieve that would be to run the whole lot on 
Linux, to be honest!  Given that it's Windows software:

- ensure you're running Windows-10 as it has more precise time functions.

- ask the developer to check for and use the 
"Get­System­Time­Precise­As­File­Time" function to take advantage of the 
increased precision.

- use a GPS with a PPS feed and ideally a PC with a real COM port, or at 
least a 3rd-party COM port.  NOT a COM port over USB!

- install the reference version of NTP (which includes PPS support for 
Windows).  It does a lot more than a simple NTP client will do.  I have some 
notes to help configure here:

https://www.satsignal.eu/ntp/Sure-GPS.htm

That's using a board which is no longer available, but a cheap Chinese GPS 
board with PPS output will suffice, possible needing a TTL to RS-232 level 
converter.  Search that page for "loopback-ppsapi-provider.dll" as the 
original method of replacing the serial port driver no longer works under 
the current Windows-10.

- leave the PC 24x7 on at as near constant temperature you can get.

Have fun!

Cheers,
David
-- 
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Email: david-taylor at blueyonder.co.uk
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