Wireless GPS Receivers

Trekker users can now enjoy the comfort and flexibility provided by a wireless GPS receiver. Bluetooth GPS technology is evolving rapidly both in performance and precision and there exists a wide selection of Bluetooth receivers on the market, featuring different characteristics. You will find below information on the RoyalTek RBT-2100 and Globalsat BT-338 GPS receivers.
Because of continual advances in Bluetooth GPS technology, the receiver shipped with Trekker can change without notice. Please visit our website for an updated list of devices shipping with the system.

The Trekker team takes great care in selecting and extensively testing receivers according to the following criteria:

Easy operation

The SiRF III receivers are amongst the smallest and lightest. Provided with a leather clip-on case, the receiver can be fixed to any convenient place. Some product line, like the Royaltek receivers, have an On/Off switch, enabling a blind person to easily know the state of their receiver. Other receivers use a push button. In this case, a power saving feature to avoid discharging when not in use is a key factor.

Autonomy 

The selected receiver has at least as much autonomy as the PDA. For a simple recharge operation, the Trekker system comes with a power splitter that can be plugged into the power adapter and then used to recharge simultaneously the GPS receiver, the speaker and the PDA.

Technology

The SiRF star III receivers represents a new generation of receivers characterized by:

• a short delay to acquire satellites and determine the initial position ( Time-to-Fix ).
• a high sensibility. The sensibility will help the receiver to get information from more satellites for a longer time thus providing more coverage. In some circumstances, higher sensibility produces more fluctuations in the number of satellites in view and a promptness to wave reflection effect (multipath) that can affect accuracy. This effect is corrected by means of the software or the type of antenna.

The Trekker team performed geodesic precisions test on predefined circuits and different weather and time circumstances to compare the Bluetooth receivers available. The selected receivers reported a higher sensibility and accuracy level. The receivers performed homogenously in pedestrian, free and motorized navigation modes.

Bluetooth connection

Stability in the Bluetooth connection is an important factor when choosing a Bluetooth receiver. You do not want to have to re-connect every five minutes. The Maestro and Trekker platform's Bluetooth Manager has been finely tuned to bring our users a robust and easy to connect to interface. The GPS receiver's Bluetooth software also plays a key role in connection stability.

RoyalTek RBT-2100 GPS receiver

On the right side of the RoyalTek GPS you will find a Power Switch and a rubber cover. Slide the Power Switch back and forth to power On/Off. When you open the rubber cover with your fingernail, you will find a Power Jack, and an External Receiver Port.

The LED Indicators are located on the face panel, underneath the RoyalTek label and described from left to right as follows:

The Battery Status LED (Roy): Yellow - Red

A constant yellow light indicates that the GPS is connected to the power outlet and charging. A Blinking red light indicates the Battery level is low - Charging immediately is required.

The GPS Status LED (al): Green

A constant green light indicates that the GPS receiver is powered On but the GPS position is not fixed. A blinking Green light indicates the GPS position is fixed. 

The Bluetooth Status LED (Tek): Blue

A Blinking Blue light indicates Bluetooth is in connection.

Make sure the battery is fully charged before using the Bluetooth GPS. When charging, connect the AC/DC adapter (with the Power Splitter) to the GPS power jack, and plug into an electrical outlet. As the device is charging, the Battery Status LED will show a yellow light. It takes about 4 hours to fully charge the battery. When the battery is fully charged, the Battery Status LED will turn Off. Unplug the device and remove the AC/DC adapter. For more information visit the RoyalTek Website at http://www.RoyalTek.com.

Globalsat BT-338 GPS Receiver

The Power button is located on bottom portion of the face panel. To turn ON the receiver, press the Power button one second. To power OFF the receiver, press the Power button one second.

Power Jack: On the lower left side you will find a rubber cover. When you open the rubber cover with your fingernail, you will find a Power Jack.

The LED Indicators are located on the lower right corner of the face panel. From top to bottom, they are described as follows:

The Battery Status LED: Red - Yellow

When the LED is red, battery power level is critically low. Charge immediately

Yellow indicates that the battery is charging. It will take up to 4 hours to fully charge.

When LED is off, the battery is partially full or fully charged. A fully charged battery will provide more than 15 hours of autonomy.

The GPS Status LED: Green

A constant green light indicates that the GPS receiver is powered On but the GPS position is not fixed. A blinking Green light indicates the GPS position is fixed.

The Bluetooth Status LED: Blue   

A slowly blinking LED means that the unit is not yet connected to a Bluetooth device.

A quickly blinking LED means that the unit is connected to a Bluetooth device.

Power saving: Note that when you start the power on the BT-338, if the Bluetooth is not connected to any device within 10 minutes, the BT-338 will automatically turn off the power and all the LED will go off simultaneously.

For more information visit the Globalsat Web site at: www.usglobalsat.com

Other Bluetooth GPS receivers

With the new Trekker system, our users have the ability to try the most advanced receivers available and have a way to test those that can better fit a particular need or behave more appropriately in certain geographical situations. Trekker has a list of other compatible receivers. We do not guarantee the performance of those alternate GPS receivers with Trekker but users will be able to experiment with them.

Trekker Compatible Bluetooth GPS Receivers

 *On evaluation 

ST or XT mode

ST and XT modes are two technologies offered by the SiRF receiver. ST is the standard mode of the receiver software. XT mode is a high-sensitivity application. The X-Trac software boosts its sensibility by integrating signals from weaker satellites. Because of this, it needs more time to fix and to calculate its position, resulting in lagging position information. Thus, the XT mode is not recommended in vehicle mode because it lags when accelerating and decelerating, and speed information is often unavailable.

Time-To-Fix factor

The time-to-fix (TTF) is the time it takes for a GPS receiver to acquire satellite signals and determine the initial position. You need at least 3 satellite fixes for the GPS receiver to be able to triangulate its position, but the receiver will perform better with 4, 5 or more satellites. As we have seen in the past, one of the main annoyances with GPS devices is the long time it takes them to acquire a fix when the device was switched off for a long time (longer than a few minutes). This is mostly due to the fact that the satellites have moved on, and the receiver needs to get a new set of trajectory information to start acquiring satellites. The new SiRF receivers feature time to fix improved performance.

Three factors are given for TTF performances:

Cold Fix:

Considered when GPS receiver is off for more than 4 hours, but not more than months.

Warm Fix:

Considered when GPS receiver is off from 20 minutes to 2 hours.

Hot Fix:

Considered when GPS receiver is off for a period under 20 minutes. 

Accuracy factor

The accuracy of a GPS receiver depends upon satellite geometry, multipath effect and atmospheric or ionosphere effects.

In fact, satellite geometry is the most important factor of those. The best spatial distribution of the satellites is to have one satellite directly overhead and three more on low horizon, 120º apart from each other. The deviation from an ideal geometry will result in less accuracy.

Multipath is when satellite information wavelength bounces off some building or objects and then reaches the receiver. This bouncing causes degradation of the signal, and thus, considerably affects the accuracy of the GPS. Some receiver software are designed to mitigate against multipath, other techniques reduce multipath through antenna performances.

Urban Canyon and foliage are sources of GPS signal derivation and inaccuracy. Buildings cause reflections of the signals, which will end in multipath problems. The XT mode of some GPS receivers may keep fix longer, but are still sensible to inaccuracies due to multipath.