DOC 4380A
4380A O & M Manual
25
098-00723-000
– Jul 2017 Revision 4.0
SyncSystem 4380A O&M Manual
A coarse calibration of the 4380A is accomplished by accounting for the individual system delays and
combining them to determine the overall delay of the system. This method is generally less accurate
because the individual delays in the system are estimated and may not be entirely accurate. Equation 2-2
gives the general formula for performing a coarse calibration of the 4380A.
sec)
/
(
_
)
(
_
_
_
)
(sec
_
meters
Velocity
Signal
meters
Cable
Antenna
of
Length
onds
delay
antenna
Eq. 2-2
The
Signal_Velocity
refers to the velocity of the GPS signals as they travel through the antenna cable. This
information can be obtained from the manufacturer of the cable. It is typically specified as a percentage of
the speed of light and it is up to the user to calculate the actual
Signal_Velocity
. Calculation of the
Signal_Velocity
is shown in Equation 2-3. It is calculated using the speed of light and the
Velocity_of_Propagation
given by the cable manufacturer. If the
Velocity_of_Propagation
is not available
or the accuracy of the PPS signal is not important to the application, then 0.85 may be used as a typical
value.
pagation
of
Velocity
meters
Velocity
Signal
_Pro
_
*
299792458
sec)
/
(
_
Eq. 2-3
Once the 4380A delay has been calculated, it must be entered into the system using the
antenna_delay
command. The example below is using a delay value of 118.5ns. Once the antenna delay value has been
properly set, use the
save
command to save the current delay to ensure the system uses the correct delay
value after a reboot or power cycle. Users can verify the value was set properly by using the
settings
gps:antenna_delay
command and reviewing the settings.
The new delay value will take effect immediately and could cause an alarm if the delay value forces the
UTC(UNSO) offset to be larger than 100 ns. The system will steer the internal clock to remove the antenna
delay. If the alarm light came on it will go out once the UTC Value is /-100. The 4380A outputs
will now be accurate to the coarse calibration accuracy specified in Appendix A.
4380A>antenna_delay 1.185E-7
[OK] 2015-08-05T16:43:29Z
4380A>settings gps:antenna_delay
1.185000000000000e-07
[OK] 2015-08-05T16:55:38Z
2.7
On Time Point (OTP)
The OTP of a system is defined as the point at which the timing signals coincide with UTC(USNO).
Typical systems use distribution amplifiers and cabling to distribute timing signals from a single source to
multiple users. This distribution network will delay the timing signals and affect their accuracy. For this
reason, it is important to select an appropriate OTP so that the desired timing signals are accurate when
they reach the user.
This section describes calibration of the 4380A assuming that the OTP of the system is the rear panel of the
4380A. This is not generally a convenient location for the OTP of the system because there will be a delay
associated with the distribution of the signals to the user. Figure 5 illustrates how to move the OTP of the
system from the rear panel of the 4380A to the user inputs. In moving the OTP of the system, it is
imperative that the distribution delays from the 4380A to each of the users is equal. This will ensure that
all users receive accurate timing signals.
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