THE RADOME OR OPEN-ARRAY ANTENNA sitting atop your boat is your radar’s eyes and ears, and like the eyes and ears upon your own head, the way it’s situated can make a world of difference in what it sees and hears. When it comes to radar, of course, the way it sees is the way it hears. Think of your radar antenna as a loudspeaker and microphone, all in one. The loudspeaker shouts — with a microwave
pulse — and the antenna listens for an echo. Then the processor crunches a few
numbers and, voila, a blip appears on your screen.
The radar antennas on most boats today transmit microwave pulses with a magnetron,
then listen for those reflections that bounce back from solid targets.
A mathematical calculation using the amount of time the pulse takes
to be reflected determines the exact distance to the target. The latest
technology, Broadband radar, broadcasts a continuous transmission
wave that increases in frequency as it moves away from the radome,
hits a target, and is reflected back. The unit’s brain then uses the difference between frequencies of the transmitted and returned waves to
determine target distance.
WHERE TO MOUNT A RADOME FOR MAX PERFORMANCE
No matter how big, how powerful, or how expensive your radar is, its performance may
be limited by the way you mount the antenna BY LENNY RUDOW
When it comes to mounting a radar antenna,
higher is better, to a point (see sidebar). First
off, getting the dome above head level is a
must because you don’t want to bake yourself and your crew with microwave pulses
every time you use the radar. (This is less
of an issue with Broadband, which emits
a much lower burst of power.) Beyond the
safety concerns, height is important because
the biggest limiting factor relating to radar’s
performance is the Earth’s curvature. Those
microwave beams can’t be bent
to follow that curvature, so the
PRACTICAL BOATER | DO IT YOURSELF
Broadband radar uses a
wave transmission instead of
a magnetron pulse, producing
exceptional target resolution
close to the boat.
Most fast powerboats run with a slight bow-up
angle, which can be compensated for by placing a wedge under the dome or array during
installation. In the case of some custom or
semi-custom boats, this angle may already be
built into the radar-mounting platform.