EndRun Meridian II, User Manual

Page: 196 / 240

M e r i d i a n I I U s e r M a n u a l 176
A P P E N D I X E
177 M e r i d i a n I I 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
Cable Length Cable
Type
Number of
LNAs
Up to 250 feet
(76 meters)
Belden 9104
or equivalent
0
251 to 500 feet
(77 to 152 meters)
Belden 9104
or equivalent
1
501 to 700 feet
(153 to 213 meters)
Belden 9104
or equivalent
2
701 to 750 feet
(214 to 228 meters)
Belden 1505A
or equivalent
2
751 to 1000 feet
(229 to 305 meters)
Belden 1505A
or equivalent
3
An Installation Guide for installing a rooftop-mounted antenna and a GPS preamplifer is shown at the
end of this appendix in Figures 1 and 2.
Using Two or Three LNAs
Installation for one LNA is simple. But the physical layout of two or three LNAs is critical. An im-
proper installation can cause feedback from the output of the last LNA, through the cable shield and
back up to the antenna. This highlights the importance of properly constructed cable terminations
and double shielded cable.
IMPORTANT
Proper installation of two or three LNAs is critical:
Use the appropriate cable as specified in the previous section Long Cable Runs .
Ensure properly constructed cable terminations.
LNAs must be installed in a straight line down from the bottom of the antenna (no bends or loops).
An improper installation may create problems for your GPS receiver and any antennas nearby.
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 two or three preamplifiers: