The Offset setting in the GNSS configuration window (INTERFACES > GNSS 0 > "Edit") allows you to enter an offset to the GNSS time and 1PPS reference in order to account for antenna cable delays or other latencies (entered and displayed in nanoseconds).
By setting the correct Offset value, you can offset the system’s on-time point by the Offset value to compensate for the antenna and in-line amplifier delays. Under typical conditions, the expected cable and amplifier delays are negligible. You can calculate the delay based on the manufacture’s specifications.
The offset range is ±½ seconds (= ±500 ms, or ±500 000 000 ns). The default value is 0 nanoseconds, and the resolution is 1 nanosecond.
D = (L * C)/V
D = Cable delay in nanoseconds
L = Cable length in feet
C = Constant derived from velocity of light: 1.016
V = Nominal velocity of propagation expressed as decimal, i.e. %66 = 0.66 Value is provided by cable manufacturer.
When using Spectracom LMR-400 or equivalent coaxial cable, this formula equates to approximately 1.2 nanoseconds of delay per every foot of cable. To calculate the Offset value (cable delay), multiply the length of the entire cable run by “1.2” and then enter this value into the Offset field.
Examples of LMR-400 (or equivalent) coax cable delays:
100 feet of cable = 120 nanoseconds of cable delay
200 feet of cable = 240 nanoseconds of cable delay
300 feet of cable = 360 nanoseconds of cable delay