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DOC 6501_Release V
ATS-6501 Users Guide
37
[4]
[epoch] gps
[format] B
[signal_word] 120
[type] irig
Warning:
The user configuration for the specific output formats are stored on the system itself.
Replacement modules will automatically be configured with the correct output format as long as
the replacement card is installed in the same slot. Moving the output module to a different slot
causes the system to configure
2.5
Antenna Delay Calibration
Utilizing the ATS-6501 as a precise time recovery system requires a complete calibration of the
ATS-6501 and distribution system. Cables and distribution equipment external to the ATS-6501
affect the calibration of the overall system and will result in an offset from UTC(USNO). This
section assumes the on-time-point (OTP) of the system is the rear panel outputs on the ATS-6501.
This may not be the desired location for the OTP; users should refer to section 2.6 for information
on changing the location of the OTP for the system.
For applications requiring the highest level of accuracy, the ATS-6501 should be calibrated at
Microsemi. This process involves installing the user’s antenna and antenna cable at the factory
and comparing the PPS outputs to a system which has a known offset to UTC(USNO). Once the
calibration is complete, the antenna delay value is provided to the customer when the unit is
delivered to the user. The PPS outputs will be accurate to the precise calibration levels specified
in Appendix A as long as the user installs the antenna at a surveyed location. If a surveyed
antenna location is not available, the ATS-6501 can be used to survey the location. See Section
2.3.5 on determining the antenna position.
A coarse calibration of the ATS-6501 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 ATS-6501.
)
sec
/
(
_
)
(
_
_
_
)
(sec
_
ATS_6501
ond
meters
Velocity
Signal
meters
Cable
Antenna
of
Length
onds
Delay
=
Eq. 2-2
The
Signal_Velocity
refers to the velocity of the GPS signal as it travels 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
_Pro
of
Velocity
ond
meters
Velocity
Signal
_
*
299792458
)
sec
/
(
_
=
Eq. 2-3
Once the ATS-6501 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