How does a marine satellite dish work?

If you’ve ever aimed a satellite dish you’ll know it has to be very precise. Even a slight misalignment can cause the dish to be aimed miles off course. It should seem amazing to you that a satellite dish can work on a boat that’s always moving. Truth is, it is amazing.

How can a dish stay aimed when the boat’s in motion?

The real key to an “in-motion” dish is the ability to move the dish in real time, with very little delay. Marine dishes use fast computers to make sure that they’re able to respond quickly when the boat moves unexpectedly. They use powerful, instant-on motors that can move the dish in tiny, tiny steps when it’s called for. The whole package is within a weatherproof enclosure that lets the dish move on three axes whenever it needs to.

The real key is trying to figure out when the dish needs aiming, and in what direction.

Using gyroscopes

The simplest way to keep a dish aimed is with a gyroscope. A gyroscope is a tool that was invented thousands of years ago. You might have had one as a toy when you were a kid. Does this look familiar?

What’s neat about a gyroscope is that the heavy spinning wheel in the middle lets it keep its position in 3D space even if other things move. You might remember getting the gyroscope spinning and then moving the base all around. The gyroscope stayed steadfastly pointed in exactly the same direction.

The gyroscope is more than a toy. If you take a gyroscope and seal it in a case, you can use gears and measuring devices to figure out where YOU are in 3D space. After all if the gyroscope isn’t moving and the measuring devices show movement, then YOU must be moving. A gyroscope is the basis for a plane’s altimeter and it also works with GPS satellites to make your car’s nav system work.

You can also use a gyroscope to figure out where the boat is going in 3D space and then move the dish to compensate. This is the most basic form of aiming and it can be used very reliably most of the time. However all gyroscopes are “a little” imperfect. Over time if you only relied on this method you would lose signal as those little errors add up.

Beam shoulder management

There’s a far more precise way of keeping a dish aimed, but it’s expensive to do. It takes some massive computing power to make sure it can be done fast enough.

See, the beam coming from your satellite is shaped like a bell curve. You might know bell curves as the way that we measure everything from voter turnout to fruit tree yield. With statistical analysis, the bell curve gets hauled out to prove that if you’re doing it right, most people/things/events fall in the middle, and the further you get from the middle the fewer people/things/events there are. It looks like this:

It also just happens to be the way that electromagnetic beams work, whether it’s a flashlight or a satellite transmission. The exact middle is strongest, and it gets weaker slowly as you move away. About 1/3 of the way off axis, it begins to drop off sharply.

Superfast computers in marine satellite dishes can measure in real time whether a signal is getting stronger or weaker. They can adjust the aim so that it’s somewhere in the center of that bell curve by detecting when the signal gets to the “shoulder” part of the curve. In the picture above, that’s the line where 34% turns into 13.5%. In satellite transmission, the shoulder is the part of the signal where you might get signal and you might not. Keeping the beam between the shoulders is the goal, obviously.

In order to keep a satellite aimed this way you need to be constantly measuring and comparing. You also need to have software that can measure the beam on two axes so that you can aim properly. If it’s a multi-satellite dish you need to be measuring all the satellites at once and comparing all your data in order to create a 3D model of where you are in space and then where you just were, so you can design a plan for putting the satellite in a place where the signals improve.

It will boggle the mind if you think about how hard this is. Yet it’s the most accurate way of aiming and it’s part of why dishes are so expensive.

Working hard to give you viewing satisfaction

Whether using gyroscopes, beam measurement, or both, a marine satellite dish has to adapt extremely quickly so that there is no interruption in service. Today’s dishes from Intellian and KVH do just that and that’s how it becomes possible to get satellite service no matter how fast you’re moving, no matter how rough the seas. The only thing that can stop these dishes is weather so bad that the signal just can’t get through.

And really, I suspect they’re working on how to fix that.

About the Author

Stuart Sweet
Stuart Sweet is the editor-in-chief of The Solid Signal Blog and a "master plumber" at Signal Group, LLC. He is the author of over 9,000 articles and longform tutorials including many posted here. Reach him by clicking on "Contact the Editor" at the bottom of this page.