SECTION TWO - Installation
About the antenna cabling
antenna is desired. The AN205-P doesn’t require any ground and is porta- ble, an advantage when it must be moved from one vessel to another. The “combo” antenna should be located where it has a clear view of the hori- zon, but is not the highest point on the vessel. Keep the combo antenna at least six feet away from objects that can “shade” GPS or differential sig- nals.
If poor GPS Signal-to-Noise Ratio (SNR) readings are obtained after the unit has been running for several minutes, check that you have the proper length of cable, and verify the quality of the antenna location and the quality and proper termination of the connectors. SNR should be as high as possible. Values of 15 and higher are preferable; anything below 10 could indicate poor reception.
Supplied with your 961 system is a 50 foot-length of RG-59 coaxial cable to use with either the AN150 or the AN205-P. The length of coax cable to the AN150 antenna must be no less than 50 feet and no more than 100 feet; to the AN205-P, no less than 20 feet and no more than 50 feet. When installing antenna cable, don’t bend it tightly in any places, and fasten the cable along its length to avoid chafing or whipping of any kind. Coil up any unused length of cable. Secure the cable well (the center conductor is solid wire), and securely fasten all cable connectors.
Installing the AN150 antenna
Whereas a loran or differential antenna should be mounted high on the vessel for best performance, the GPS antenna should be mounted as low as possible and out in the open to avoid “shading” (placement of the antenna where it is partially obscured by another object from the signals it must receive). If mounting on top of a tower or mast, understand that the unit will be affected by the pitch and roll of the vessel. Often the bow or stern will provide a location where shading is minimized, while serving to keep the antenna low. Be sure that any directional L-band transmitting antennas (such as radar or satellite communication antennas) can never point at the GPS antenna--its internal preamplifier is quickly destroyed by such radiation.
Page 16 | 961 INSTALLATION MANUAL Revision A |
