148 marine electronics installation and troubleshooting
Troubleshooting Satellite Systems
A proper satcom installation typically con-
cludes with a series of calibration tests for the
fluxgate sensor and operational tests for the
receiver. These tests are for electronicsspecial-
ists only, however, and are therefore beyond
the scope of this book.
However, as the owner or electrical techni-
cian, your troubleshooting should confirm the
basics of a proper electricalinstallation as follows:- wiring links between the system’s compo-
nents are in order - power is getting to the devices
- any manufacturer-required grounding is
in good order - sources of RFI and EMI have been avoided
or eliminated
There are many systems available world-
wide, as shown in Table 14-2. The onus is on
the electronics technician to be aware of the
special needs of this equipment. Aside from
minor troubleshooting of the sort I’ve described
above, most issues related to satcom equipment
are best dealt with by factory-trained specialists.
In fact, many warranties require that the equip-
ment only be installed by such specialists.Position-Finding Systems
Over the course of just a few decades, naviga-
tion has evolved from paper charts, dead reck-
oning, and sextants to almost universal pene-
tration of electronic methods. It began with
systems like Loran-A and Loran-C, and early
satellite navigation (satnav), which gave a posi-
tion fix every 90 minutes or so (if you were
lucky). Then electronic position finding
evolved to become virtually synonymous with
the satellite-based global positioning system
(GPS), which gives us essentially real-time
information of phenomenal resolution.The first GPS units became available to
boaters in the late 1980s. They held a lot of
promise, but were extremely expensive, and the
fact that the full satellite system was not in place
left voids in the coverage at certain times of the
day in some geographic locations. At one point
in the early 1990s, the system seemed to be
working quite accurately. Then the Gulf War
began, and the U.S. government imposed
Selective Availability (SA), which “detuned” the
inherent accuracy of the GPS system for mili-
tary reasons. During this time, however,
enhancements were introduced to recover the
inherent potential accuracy of GPS. These
included Differential GPS (DGPS), which was
a supplemental shore-based radio system simi-
lar to Loran-C, and WAAS (wide area augmen-
tation system), a system of additional satellites
and ground stations that corrected GPS signals,
further improving the system’s accuracy. SA was
turned off by President Clinton in 2000, but it
could return at any time.
As of this writing, the industry seems to
have settled on WAAS-enabled equipment,
which is accurate enough to pinpoint your
location anywhere on earth to within 3 meters
(about 10 feet) 95% of the time.
Today, GPS is the heart of virtually every
electronic navigation system and is perhaps one
of the most interfaced devices on board. To use
NMEA parlance, GPS is the primary “talker”
aboard most modern boats, sending its data to
many other devices—the “listeners.” It’s quite
common to have a single GPS receiver linked to
one or more repeater displays, an autopilot, a
VHF radio, radar, and a computer. Proper GPS
installation and performance is key to both the
functionality of many devices on board and the
safety of the boat and crew.GPS Installation and Troubleshooting
The major GPS installation component is its
antenna, so we’ll cover that here, instead of in