Installing Your Own Radar

ered. Follow the procedures described above for determining any compass deviation and getting power to the receiver. The big consideration is where to locate the GPS antenna. GPS receivers use receive-only antennas that need a clear view of the sky at all times. Even something like a Bimini top or a windscreen can affect the integrity of a GPS signal. Also, radio transmissions from other electronic equipment such as cell phones, VHF radios, and single-sideband (SSB) radios can affect a GPS signal.

The rules here are simple and not too hard to comply with, even on small boats. Basically, the ideal is to maintain about a 1-meter separation, or a little less than a yard, between transmitting antennas and the GPS receiving antenna. On most boats this is simply a matter of mounting the VHF antenna on one side of the bridge and the GPS antenna on the other. Mission accomplished! On boats with elaborate gear-mount brackets and airfoils, just keep from mounting these antennas adjacent to each other.

GPS is a line-of-sight system between the antenna and satellites orbiting overhead. The antenna scans the sky via a conical pattern that points straight up. So, unlike VHF, mounting an antenna too high can actually be detrimental to its performance in a rolling, pitching sea, particularly if you have selected the improved accuracy provided by a differential receiver. An antenna mounted too high will drive the GPS unit crazy as it swings back and forth trying to find its exact location. Low and as close to the centerline of the boat as you can get is the way to go with this installation. Any of the commercially available mounting brackets for these antennas will do just fine, but don’t think you’ll improve performance by using an extension pole, as you might with a VHF antenna.

If you have a differential GPS receiver (DGPS), one that also receives radio position data from landbased stations in addition to satellite signals, you may need an additional positive and negative wire to the antenna.

As with fish-finder and depth-sounder transducer cables, your GPS antenna comes with a fixed-length cable for attachment to the display unit. Don’t alter its length, and keep any extra cabling coiled away from other cables and harnesses. Figure 12-13 on page 190illustrates a typical wiring hookup for a GPS without DGPS. Figure 12-14on page 190 illustrates a typical installation with a DGPS receiver.

In the old days, the average boatowner wouldn’t have dreamed of installing his or her own radar. Today, radar manufacturers have come a long way, and owner installation is not only practical but not that difficult.

The big consideration with radar is the mounting of the antenna (scanner). Four basic rules must be followed:

Install the scanner on your cabintop or on an appropriate mast with a platform designed to accept the mounting bolts.

Position the scanner so that the antenna gets a good all-around view with as few parts of the superstructure or rigging as possible intercepting the scanning beam. Any obstructions will cause shadows and blind sectors on the radar screen.

To minimize electrical interference, don’t route the cabling from the antenna near any other onboard electrical equipment or cabling, just as with other gear mentioned above.

Remember that a radar antenna creates pronounced compass deviation. Keep a separation zone of about 51⁄2 feet (1.7 m) between the radar antenna and your compass.

When installing an antenna on a powerboat, consider the average angle at which your boat cruises while underway. If the antenna is mounted perfectly level with the boat at the dock, it will tend to aim at the stars while underway. Figure 12-15illustrates the static angle for the antenna and the effect this slightly downward mounting has on the beam while the boat is underway. To determine the exact angle of the antenna to use, spend a morning determining the amount of lift your boat goes through from a standstill to cruising speed. Once

10 - 15°

Fig. 12-15. Static angle for powerboat radar antenna installation.

Fig. 12-16. Typical wiring hookup for a radar system.

you have established this angle, you’ll know how many degrees to tilt the forward edge of your radar antenna downward for optimum scanner performance while the boat is under way. Typically this number is around 10 or 15 degrees.

The antenna has a definite front-facing position that must be observed. Follow the manufacturer’s installation instructions if you’re not sure how to achieve this important orientation. Also, as with the other gear mentioned, the cable that comes with the radar is of a calibrated length that should only be altered by installing a factory-supplied harness, which is available in different lengths.

One last thing regarding the radar antenna: All closedarray scanners (those with a fiberglass enclosure) come with a condensation drain valve on the bottom shell of the antenna housing. Make sure this drain is unobstructed and working as it should at all times. Condensation buildup inside the antenna housing will destroy the expensive circuitry in there.

Once the antenna is mounted and the lead is fed to the approximate location of the display, permanently mount the display. Again, ergonomics is important. Radar is useless if you don’t have a clear, unobstructed view of the entire display. Connect the display to the dedicated instrument bus for positive and negative return, run a ground from the back of the chassis (at the wingnut and stud) to the negative bus bar, connect the antenna cable to the appropriate socket, and you’re ready to go! Figure 12-16 illustrates the wiring hookups for a typical radar installation, with some of the other mentioned concerns pointed out in the diagram.

I have one last general note regarding electronic equipment: Never attempt to use this gear until you’ve read through the fine points of the owner’s manual and documentation that comes with the equipment. In most cases, before the gear can be used effectively there is an initialization or preliminary tuning procedure that must be followed. Be familiar with these steps, and make sure you take them before you head off into the sunset. The equipment available today is good, but it’s not completely magical; it needs user intervention to give the best results. Scanner

May have a chassis ground Fixed length cable DC + DC -

DC DC +