EndRun RTM3205, User Manual

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R T M 3 2 0 5 U s e r M a n u a l 130
A P P E N D I X E
131 R T M 3 2 0 5 U s e r M a n u a l
I N S T A L L I N G T H E G P S A N T E N N A
Two LNAs
GPS Antenna
One-foot cable
LNA
One-foot cable
LNA
Up to 750 feet (228 meters) of cable
RTM3205 Precision Timing Module
Other Accessories
Lightning Arrestor
A lightning arrestor helps protect your GPS installation from damage due to lightning strikes. It is
designed to pass the DC voltage that is needed to power the antenna and/or preamps without degrad-
ing the GPS signal. It is installed between the antenna and the receiver where the cable enters the
building, near an earth-ground. You must bond the lightning arrestor to the earth-ground.
Signal Splitters
Signal splitters are used when two GPS receivers are sharing one antenna installation. The smart
GPS Splitter supplied by EndRun is a one-input, two-output device. In the normal configuration, one
of the splitter RF outputs (J1) passes DC from the connected GPS Receiver through the splitter to the
antenna, allowing the GPS Receiver to power both the antenna and the splitter amplifier. The other
RF output (J2) is DC loaded with a 200-ohm resistor to simulate the antenna current draw.
When selecting and installing a signal splitter keep these points in mind:
1. The splitter must be DC-blocked on one leg. The GPS Receiver in EndRun’s products provide
+5 VDC up the coax to power the GPS antenna’s built-in preamp. The two GPS receivers connected
to the splitter outputs must not have their power sources connected together.
2. It is desirable that the DC-blocked leg has a DC load resistor to simulate a GPS antenna load.
This way you will not get a false alarm from the GPS Receiver’s antenna load sensor. However, the
RTM3205 allows you to mask an antenna fault alarm from causing a system fault by using the
se-
tantfltmask
command. See details in
Chapter 3 - Console Port Control and Status
.
3. The signal splitter supplied by EndRun has a built-in preamplifier to compensate for signal loss
through the splitter. If using a splitter other than the one supplied by EndRun you may need to com-
pensate for splitter signal loss by using a separate GPS preamplifier.
Three LNAs
GPS Antenna
One-foot cable
LNA
One-foot cable
LNA
Up to 1000 feet (305 meters) of cable
LNA
One-foot cable
RTM3205 Precision Timing Module