24
Description
T801-4 Installation and Operation Manual
© Tait Electronics Limited September 2007
POWER LED
This green LED is lit when the internal DC supply is active (on).
GPS SELECTED LED -
PORT A
This yellow LED is lit when the external GPS receiver on
PORT A
is
selected.
GPS SELECTED LED -
INT/PORT B
This yellow LED is lit when either the internal GPS receiver, or the external
GPS receiver on
PORT B
is selected. The default setting for this LED is to
indicate whether the internal GPS receiver (if fitted) has been selected. It
can be configured to indicate the status of an external GPS receiver
connected to
PORT B
by using the DIP switches and internal links (refer to
“Setting the Links on the System Interface Board” on page 50
).
1PPS VALID LED
This green LED is lit when the 1PPS input to the T801-4 from the selected
GPS receiver is valid.
1PPS TTL OUTPUTS
These four BNC connectors provide 1PPS outputs at TTL levels. They
have low output impedance, and the output drive is designed to drive a 50
Ω
load.
When these outputs are used with a load, each output must be terminated
with a 50
Ω
termination, otherwise reflections of the 1PPS pulse may occur.
When the outputs are not used, they should be left un-terminated.
When the outputs are used to drive the 1PPS input on TB9100 system
interface ports, up to six of these ports can be daisy-chained from a single
output (as shown in
Figure 1.5 on page 25
). The maximum overall cable
length in this situation is 30 metres.
If loads are to be daisy-chained, we recommend that the cable length
between the first and last load is kept to a minimum. This will reduce any
1PPS propagation variation between base stations. The propagation of the
1PPS pulse is delayed by
≈
5ns for every metre of 50
Ω
coaxial cable used.
The DIP switches on the rear panel provide the option of disabling these
1PPS outputs when the GPS fix is deemed invalid.
Ground Connector
A threaded M5 chassis ground connector is provided on the rear panel. This
stud allows the connection of a ground cable terminated with a “ring”
terminal.
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