GPS and radio clocks communicating with your server via a
serial port connection are subject to serial port delays and other operating system dependent propagation errors. In some cases long
antenna cables may introduce further signal propagation delays. For this reason it is important to calibrate your clock for use with
your time server.
NTP driver calibration is easiest achieved using the NTP4 Query Command Line Tool.
The screenshot above shows a test system running a Spectracom 8189 clock as primary time
source and a local area network NTP server 192.168.1.19 as secondary time source. Two public NTP servers on the internet facilitate
external verification of test results. The two servers on the internet are subject to round trip delays on the order of 300ms as well
as substantial network jitter and therefore exhibit greater offsets with respect to the local system clock than the local area network
You can use the time1 driver parameter to compensate for signal delays and other propagation errors. The example shown above
illustrates how to compensate for a nominal 6 millisecond error. The final screenshot shown below shows both time sources in agreement
to within 2.5 milliseconds. Depending on your requirements you might wish to calibrate to within closer specifications.