Specifications

Model E8 Series Operation Manual
E8 Series A5 Manual 9 October 2008
Page 5 of 12
E8 Series GPS Timing & Frequency Reference
Introduction
The GPS clock is shipped ready for operation. No adjustments are needed to have a 10MHz
frequency reference and 1 pulse per second time reference within 20 minutes of initial switch on.
The status of the GPS lock is shown on four LEDs on the front panel.
For more information as to satellite signal strengths, etc, a computer with RS232 may be connected
to the interface. A freeware program such as WinOncore may be used to display information from
the GPS receiver.
Installation
The antenna should be installed, preferably with a 360 degree view of the sky. However the receiver
is very sensitive and will give good results with the antenna on a window ledge, or even inside a
building. The satellite signal strengths may be checked after installation using a computer with
suitable software connected to the RS232 interface. The DC power supply should be connected. The
unit will operate with any voltage between 6 and 15V DC. Current consumption for the E8-X is
about 250mA max and the E8-Y about 300mA continuous, 500mA maximum warm up. A universal
line power supply is provided.
Operation
The unit is fully programmed to operate without adjustment anywhere in the world. The GPS
receiver will take about 1 minute to obtain a fix from a cold start with unknown location. The
receiver then does a "site survey" for about 15 minutes, averaging the positions obtained. After the
site survey is complete, the receiver switches to position hold mode, and uses all the satellites
available to improve the accuracy of the time calculation. At this point the unit will lock its 20MHz
reference oscillator to the GPS signal. This only takes a few seconds. When the PLL locks the red
"lock" LED should go out, but may flash for a further minute as the PLL settles. The normal
operating condition is with the red "lock" LED off.
The status of the satellite tracking is shown by the green and amber LEDs. The normal situation is
that the green LED shows a long flash, followed by a number of short flashes. The number of short
flashes shows the number of satellites being tracked, and included in the time solution. The amber
LED may also flash. This shows the number of satellites being tracked, but not included in the
timing solution.
If the red "lock" LED should start to flash at about 1Hz rate, this indicates that the phase error
between the GPS signal and the internal 20MHz oscillator is greater than a pre programmed
threshold. This does not indicate that the 10MHz output is unlocked. During normal operation the
GPS receiver estimates the accuracy of the timing solution using the "TRAIM" algorithm (Time
Receiver Autonomous Integrity Monitoring) developed for the Motorola Oncore receiver. If the
predicted timing error is greater than the programmed limit, the receiver will switch into standby,
and the red lock LED will turn on. The 10MHz output and 1pps output will then drift according to
the ambient temperature and aging of the internal oscillator. The unit should never go into standby
during normal operation. The most likely reason for doing so is a major antenna fault.