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What is GPS?
How Does it Works?
What are the uses for GPS?
Are there any charges for using GPS?
How accurate is GPS?
What is WAAS?
What is NMEA?
What is Selective Availability (SA)?
What are sources of errors for GPS?
What is Differential GPS (DGPS)?
How do I get local time displayed? What about daylight-saving time?
What is a map datum? Which map datum do I use?
What is a Waypoint?
What is a Route?
What is a Track Log?
Are there benefits to having a unit that uses WAAS for my car or truck?
Why is my unit not locking on to any satellites?
Will my unit work in bad weather?
How long is the battery life?
What is the difference between 12 channel and 16 channel?
How do I obtain service for my unit?

What is GPS?
The Global Positioning System (GPS) is a satellite-based system that allows you to pinpoint your exact location anywhere on the planet. The system consists of 24 satellites orbiting above the Earth. Using a GPS receiver, the satellites allow you to determine your location with great precision. Originally developed for military use, the GPS satellite system has been opened to the general public. The GPS system is maintained by the U.S. government with taxpayer dollars, and there is no charge to use the system with a GPS receiver.
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How Does it Works?
The mechanics of the GPS system are complex. Provided here is a simplified description that avoids the complex details:

• The exact position of each satellite is carefully maintained by the government, aided by an automated ground-based system for correcting any errors.
• A GPS receiver can then calculate its position by determining the distance to each satellite. To perform the necessary calculations to a high degree of accuracy, a GPS receiver must receive data from at least 3 satellites.
• The GPS receiver can then provide 2-dimensional positioning (latitude and longitude). Locking onto a 4th satellite will provide 3-dimensional positioning (latitude, longitude, and altitude). Position is continually updated at a high rate (typically once per second).

What are the uses for GPS?
There are countless uses for GPS, in both commercial and recreational applications. Here are a few examples:

Surveying	Boating	Marine navigation	Hiking	Aircraft navigation
Fishing	Agriculture	Camping	Transportation Industry	Automobile navigation

GPS can be used whenever it is desired to mark a location, after which it will be easy to return to the same spot. These are called "waypoints", which are stored in the GPS receiver. GPS can also be used whenever directional guidance is desired.

Example 1:
You are camping, and plan to go hiking through the woods. You can mark your current location (saving a waypoint). It will then be easy to find your way back to the campsite.

Example 2:
You are fishing and come across a hot spot with lots of fish. Use your GPS receiver to mark a waypoint so that you can return to the same spot.

Example 3:
You are visiting Chicago, and plan to visit several restaurants and museums. You can download the locations from a PC into your GPS receiver, which will then direct you to each destination. (Not all GPS receivers have a communications port for connecting to a computer).
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Are there any charges for using GPS?
NO! The GPS system is maintained by the government with taxpayer dollars, and there is no charge to access the system with a GPS receiver. Your only expense is the initial purchase of a GPS receiver.
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What is the accuracy of a GPS?
Today's GPS receivers are extremely accurate, thanks to their parallel multi-channel design. Certain atmospheric factors and other sources of error can affect the accuracy of GPS receivers. Garmin® GPS receivers are accurate to within 15 meters (49 feet) 95% of the time. Generally, users will see accuracy within 5 to 10 meters (16 to 33 feet) under normal conditions.

Under ideal conditions your GPS can be accurate to within 10 feet. Please note that the absolute accuracy at any given moment will depend on the cumulative effect of various error sources, how many satellites the GPS unit locks onto, and whether WAAS is being used. These topics are discussed in the this FAQ section. Taking all factors into consideration, typical day-to-day accuracy will vary anywhere between 20 to 50 feet.
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What is WAAS?
Wide Area Augmentation System (WAAS) was implemented by the FAA to provide improved GPS navigation for aircraft. The WAAS system consists of 25 ground-based transmitters located throughout the U.S. The precise location of each transmitter is maintained, and each location is compared to GPS distance measurements. Corrections are uplinked and broadcast via satellite. Compatible GPS units can receive this extra satellite signal, which provides significantly improved accuracy.
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What is NMEA?
NMEA stands for National Marine Electronics Association. NMEA has created a standard communication interface for connecting various electronic devices such as marine radios, GPS units, etc. Although originally created for marine use, any device can have an NMEA interface.

The GPS500 and GPS1000 offer an NMEA output. The NMEA output allows you to track your position on a map in real-time. You need to connect the GPS to a PC and run NMEA-compatible mapping software. Cobra's Rand McNally software is NMEA compatible.

The NMEA output also allows you to connect the GPS to any NMEA-compatible device. For example Cobra marine radio models MRF55 and MRF75 have an NMEA-compatible input. Connecting a GPS allows you to see GPS information on the marine radio. And even better, it allows sending a distress signal with your coordinates so that the Coast Guard can find you!
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What is Selective Availability (SA)?
Selective Availability was incorporated into the GPS satellite system to intentionally degrade the accuracy of GPS receivers. The purpose was to prevent hostile governments from using the high precision of the GPS system. Authorized branches of the U.S. government had special GPS receivers that could fully decode the satellite signals to allow full accuracy.

The government has since decided that Selective Availability is no longer needed. Selective Availability was disabled in May of 2000, which has greatly improved the accuracy of all GPS receivers.
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What are sources of errors for GPS?
Following are sources of errors for GPS receivers:

• The number of satellites acquired: The more satellites the receiver can lock onto, the better the accuracy will be.
• The location of the satellites: Of the satellites that your GPS locks onto, the more they are scattered throughout the sky the better your GPS can "triangulate" your position.
• Timing errors: Small timing errors in the GPS receiver clock will create measurement errors.
• Multi-path: Signal multi-path occurs when the satellite signal reflects off a surface before reaching the GPS receiver. For example signal reflection off of tall buildings. This adds a small timing delay, which causes a measurement error.
• Other errors: Such as signal delay for the satellite signal to pass through the ionosphere, and small errors in the satellite's reported position.

What is Differential GPS (DGPS)?
Differential GPS is a special system that increases the precision of GPS receivers. It consists of a special transmitter in a precise location, which then transmits a correction signal. A special receiver is required, which connects to your GPS unit. The GPS unit can then make use of the correction signal to provide increased accuracy. DGPS transmitters are typically maintained by the government, and are placed in areas that have a special need for precision. As an example, the U.S. Coast Guard maintains a system of 82 DGPS sites placed along waterways to provide improved marine navigation.

Current DGPS sites cover only a small fraction of the U.S. -- limited to the areas that have a special need for the increased precision. And the special receiver adds an additional expense. Due to the added expense and limited coverage, current Cobra GPS units do not offer DGPS capability.
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How do I get local time displayed? What about daylight-saving time?
GPS units operate on UTC time. UTC is the Universal Coordinated Time or Greenwich Mean Time (GMT). You can input a local offset (or difference) from UTC so that the unit will display your local time. This option is located under the unit's operational setup. A chart is provided in products' owner's manuals to help you select the appropriate offset for your area. If needed, the chart will also show the UTC offset during daylight-saving periods.
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What is a map datum? Which map datum do I use?
A datum is a mathematical model of the Earth which approximates the shape of the Earth, and enables calculations such as position and area to be carried out in a consistent and accurate manner. The datum is physically represented by a framework of ground monuments (i.e., trig stations) whose positions have been accurately measured and calculated on this reference surface. Lines of latitude and longitude on a map or chart are referenced to a specific map datum. Every chart has a map datum reference. The map datum is usually listed in the title block of the chart.

If you are comparing GPS coordinates to a chart or map, the map datum in the GPS unit must be set to match the chart or map's datum for accurate comparison. The datum used to create a chart or map is generally listed in the legend.
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What is a Waypoint?
Waypoints are locations or landmarks worth recording and storing in your GPS. These are locations you may later want to return to. They may be check points on a route or significant ground features. (e.g. camp, the truck, a fork in a trail, or a favorite fishing spot).

Waypoints may be defined and stored in the unit manually, by taking coordinates for the waypoint from a map or other reference. This can be done before ever leaving home. Or more usually, waypoints may be entered directly by taking a reading with the unit at the location itself, giving it a name, and then saving the point.

Waypoints may also be put into the unit by referencing another waypoint already stored, giving the reference waypoint, and entering the distance and compass bearing to the new waypoint.
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What is a Route?
A route is a series of waypoints entered in the order that you want to navigate them.
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What is a Track Log?
The track log are points automatically stored when you are moving. It is the electronic equivalent of laying down a "breadcrumb trail" to mark your path. These points will be shown strung together on the map page of your unit so you can see where you have been.
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Are there benefits to having a unit that uses WAAS for my car or truck?
Absolutely. The Wide Area Augmentation System (WAAS) provides multiple benefits to automotive applications.

While there are specific limitations to using WAAS due to the signal being blocked by buildings and terrain (mountains and hills), it may prove to be advantageous in areas with multiple, closely paralleling, or intersecting streets. In these situations, the extra accuracy of WAAS helps the system correctly identify the road on which you are driving.

The additional accuracy of WAAS can also be a great tool for off-road vehicles by allowing you to pinpoint specific locations as you travel in the backcountry.

It is important to note that currently WAAS only covers the United States although parallel systems are being developed in Europe (EGNOS) and in Asia.
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Why is my unit not locking on to any satellites?

• Check batteries or external power source.
• Make sure that there are no obstructions and the unit has a clear view of the sky.
• Make sure there is no interference from VHF radios, Radars or cell phones.
• Check the status on satellites page. Allow about 20 minutes for the unit to lock on to the satellites.
• Try doing a “Reset Options” on the unit.

Will my unit work in bad weather?
GPS works 24 hours a day, anywhere in the world and is not affected by clouds, storms or weather. This is one of the advantages GPS has over Loran C.
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How long is the battery life?
The life of your battery in your handheld GPS unit depends on a number of factors. First and foremost is the quality of the batteries you are using. Be sure to select a high quality alkaline battery. Using the Power Save feature whenever possible and keeping the backlight panel off when not needed will assure maximum battery life. Depending on the unit you have, your average battery life will be between 8 and 20 hours.
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What is the difference between 12 channel and 16 channel?
A 12-channel receiver has 12 dedicated channels reserved for satellite communication. The additional channels on a 16-channel receiver provide quicker lock-on, more up to date information and the ability to stay locked-on when you are in a challenging area (a heavily wooded area or in locations where the horizon is blocked by mountainous terrain, cliffs, valley slopes or tall buildings).
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How do I obtain service for my unit?
Our manufacturers back your investment in quality products with quick, expert service. If you're in the United States and you have technical, return or repair questions, please contact the Factory Customer Service Department. Refer to the Warranty Page for information on contacting the respective Service Department.
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