GPS Antennas


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What You Need to Know about GPS Antennas

GPS devices have become very popular among anglers and boaters. They help us to find our favorite spots on the lake in hopes of catching another lunker. They let us know the spot where hazards are found. And get us safely back to dock if we get caught after dark. But most of us just buy them and assume that is that.

What You Probably Don't Know

Knowing something about the GPS antenna and the effectiveness of external antennas can make them even more useful. For example, if you are using a Garmin 12XL and you buddy is operating an Eagle Explorer, you may be in trouble. Eagles emit an interfering signal that inhibits Garmin reception. The Garmin GPS will have trouble fixing on satellites and may give inaccurate readings.

There are other things that may effect satellite reception. GPS units need to lock on to at least 4 satellites to give accurate readings. Some notify you immediately if you have lost your signal and you could have trouble getting a fix because of all the alerts. Others will wait until the signal has been lost for at least 30 seconds before letting you know there is a problem. With trees blocking the satellites, losing and reacquiring the signal three or four times a minute may not produce an alert and you will have inaccurate tracking data without know there is a problem.

You would expect tall buildings to cause problems with GPS reception. Deep canyons and valleys can cause similar problems. The type of antenna used can influence the quality of your tracking data.

Patch Antennas

Patch antennas have reduced sensitivity as they scan toward the horizon. This reduces their effectiveness inside vehicles and under tree cover and bridges. Examples are the G-12XL, EE and M-4000 GPS receivers. Their strength is in acquiring overhead signals. They also have less sensitivity to reflected signals.

Helix Antennas

Helix-style antennas are stick shaped. They have good sensitivity nearly down to the horizon. Overhead interference like the roof of a car or boat or tree cover will cause fewer problems for these. Their weakness is in picking up reflected signal and throwing off positioning.

The Remote Antenna

Adding a remote antenna to your GPS unit allows you to select the best antenna for your needs. You can choose from helix or patch type antennas, amplified antennas, and rebroadcast antennas.

Amplified GPS Antenna

The amplified antenna contains its own amplifier to boost weak signals. These need a power source such as a nine-volt battery or connection to a car/marine battery. They work well in vehicles and uneven terrain such as cities and mountains.

Rebroadcast Antenna

If you have a GPS unit that does not accept an external antenna, a rebroadcast antenna captures the signal and re-transmits it at the end of its cable. The GPS receiver then receives the broadcasted signal to fix its position. This is the solution to use when inside a car or boat. A helix antenna can also receive the signal and send it to a fixed patch antenna. A physical connection between the two is unnecessary so the GPS receiver remains portable.

Home-built Antenna

If you are unable to find a suitable antenna for your situation, it is also possible to build your own. Parts are inexpensive and many can be obtained at Radio Shack. See Links to GPS Antenna Construction Sites.








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