Where should you install your GPS antenna relative to your transucer?

I am just beginning to rig my new Humminbird 997 side imaging sonar/GPS combo. An important consideration during the rigging process is the placement of the external GPS antenna and the transducer. It is commonly believed that these two pieces of equipment must be placed as close together as possible for optimum positional accuracy relative to a particular feature observed by sonar. However, this is not the case.

It is important to remember that GPS position measurements are not exact. There is error associated with the measurement. For example, older generations of GPS receivers often had position errors of 10-20 meters. What that means is that a measurement with that much error placed your antenna (in your boat) somewhere within a circle with an area of 3378 square feet (for a 10 meter position error)....you're not sitting on an exact point, but rather you're somewhere within that big red circle shown above. A very rough position measurement, indeed!

Humminbird now offers a high-accuracy GPS receiver, the AS GR-50 that boasts an impressive 2.5 meter position error. In other words, a position measurement with the new Humminbird receiver places your antenna (boat) within a much smaller circle of possible locations. That circle (shown in purple above) has an area of 211 square feet....more than 90% smaller than previous GPS receivers. You can't argue with the math; Humminbird receivers determine your GPS position with a much higher degree of accuracy than other GPS technologies.

So, back to the original question. Do you need to install your GPS antenna in close proximity to your transducer? The answer is no. The accuracy of even a very good GPS measurement, like the one that the new Humminbird antenna provides, is such that a few feet between the antenna and the transducer will make absolutely no difference. Pick a spot to mount the antenna that has the most unobstructed view of the sky, and mount the antenna there. Don't have the antenna blocked by a windshield, by the locator's head unit, or anything else that might interfere with reception of those satellite signals beamed from so many miles above.