EndRun Sonoma N12, User Manual

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S o n o m a U s e r M a n u a l 132
A P P E N D I X E
133 S o n o m a 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
A page of the Installation Guide for installing a rooftop-mounted antenna with GPS preamplifer is
shown at the end of this appendix in Figure 2. Complete guide is here:
http://www.endruntechnologies.com/pdf/5050-0004-000.pdf
Using Three Preamplifiers
Installation for one or two preamplifiers is simple. But the physical layout of three preamplifiers is
critical. Preamplifiers should be in a straight line departing from the bottom of the antenna so that
any leakage from the downlead cable is as far from the antenna as possible. A positive feedback path
can occur from the output of the last pre-amp, through the cable shield and back up to the antenna.
This highlights the importance of properly constructed cable terminations and double shielded cable.
For installations using three preamps, we recommend that the last pre-amp be located as far as is
practical from the antenna. This is because the antenna and three preamplifers will have more than
100 dB of gain, increasing the likelihood that enough leakage from the cable can cause “round-the-
world” feedback to the antenna and set up oscillation. Here is the suggested configuration for an
antenna installation with three preamplifiers:
GPS antenna
One foot cable
Preamplifier
One foot cable
Preamplifier
Up to 1,000 feet (305 meters) cable
Preamplifier
One foot cable
Sonoma GPS Time Server
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 time servers 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: