Join our mailing list!

Find us on Facebook

You are here: Home > Buyer's Guide
Choose a sub category:
Arkon User Manuals Garmin nuvi Guide How does GPS work?
What is a Locator? How is GPS used? How to choose right GPS receiver?
Key features of GPS Receivers Major Types of GPS NMEA 0183 Protocol
What is WAAS? What to look for when buying GPS?
  • What is GPS?

The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense.

  • How accurate is GPS?

Today's GPS receivers are extremely accurate, 12-32 parallel channel receivers are quick to lock onto satellites when first turned on and they maintain strong locks, even in dense foliage or urban settings with tall buildings. Certain atmospheric factors and other sources of error can affect the accuracy of GPS receivers. GPS receivers are accurate to within 15 meters on average.

  • What is WAAS?                                                                                                                                        

 Basically, it's a system of satellites and ground stations that provide GPS signal corrections, giving you even better position accuracy. How much better? Try an average of up to five times better. A WAAS-capable receiver can give you a position accuracy of better than three meters 95 percent of the time. And you don't have to purchase additional receiving equipment or pay service fees to utilize WAAS.

GPS WAAS capable receivers:

Globalsat GPS  Bluetooth BT-359, BT-338, Holux BT GPSLim 236 / Globalsat GPS mouse BU-353, Holux GPS Mouse GR-213 and more. 

  • Differential positioning (DGPS)

Accurate measurement of the relative positions of two receivers tracking the same GPS signals.

  • What is NMEA?

NMEA-0183 is a standard for interfacing marine electronic devices. This standard defines the electrical signal requirements, data transmission protocol, data transmission timing, and specific message formats for a 4800 baud serial data interface.

GPS receivers using the NMEA protocol:

Globalsat : Globalsat GPS  Bluetooth BT-359, BT-338, Globalsat GPS mouse BU-353 and more. 

Holux :  Holux GPS Bluetooth GR-231, GR-230, 236, 240, Holux Compactflash CF GPS GM-270, 271, GM-270U and more.

HAicom : Haicom Compactflash  Haicom  CF GPS  HI-303E , Haicom  CF GPS HI-303MMF, Haicom  CF GPS HI-303S etc.
What are Cold/Warm/Hot FIX stand for?

When you first fire up a GPS receiver it has no data with which to work. It doesn’t know about what satellites to use, where they are or even what the time is.  All of that information has to be received before a fix can be calculated. Fixes that start with No information are called COLD fixes.  After receiving the time signal from one satellite, the GPS receiver can set its internal clock. It then listens for any satellite it can “hear” to send out almanac or ephemeris data WARM fixes. Once the almanac is received the receiver can then listen specifically for the satellites that are near the one satellite it can presently hear at the time. If it hears them, it knows the almanac is relatively current. Finally, the GPS receiver gets the ephemeris data about where the satellites are located in space and with this information and the time signals from the satellites it can calculate its location and present the first “fix” to your mapping software HOT fixes.  The process of a cold fix can take as much as 20 minutes, but may also be done in as little as 3-6 minutes. If you move the receiver during this first fix, the time may be extended significantly. The problem with movement is that if the GPS loses contact with a satellite in the middle of receiving an ephemeris or almanac string of data it has to wait until the next full cycle of the signals before it gets a new chance.


  • What is SiRF ?                                                         

SiRF comes as the main chipset in GPS chips in PC and Pocket PC based GPS Receivers which drives how you receive signals from the satellite.  Whether it tries to look at all 12 in view satellites, or whether it discards the weakest signals and goes for the stronger signals. The SiRF chipset has gone through a number of incarnations.  These are mainly SiRFstar, SiRFstar I, SiRFstar II, SiRFstar IIe, SiRFstar IIe/LP, SiRFstar IIt, recently SiRFLoc and SiRFXTrac were added. 

SiRF is both a chipset and a protocol, allowing you to talk directly to the chipset itself giving you greater control over the GPS with features such as trickle mode for Low Power consumption.
What is SiRF Star III chipset?

We have had a few users asking What is the SiRF Star III chipset, and why is it so important? Well, the SiRF Star III chipset is a pretty big innovation in the GPS world, as it is a dramatically better performance for getting a GPS signal from satellites and getting you a location on your GPS. The 3 key advantages of the SiRF star III chipset are 1) Faster fix times, 2) High sensitivity for better locking of satellite signals in tough areas like under dense foliage or in urban canyons of sky scrapers, and 3) Low power drain for longer battery life.

SiRF star III Chipset Faster Fix Times
When a GPS is turned on, it needs to figure out where it is by pulling down signals from several satellites before it can triangulate and figure out where you are. Sometimes this can be faster if the GPS has been recently used because they can quickly figure out that they "We were just here yesterday, and so things look the same, so I must be in the same place." These are called "warm starts" when they have a head start on their position. Cold starts on the other hand take a lot longer because the GPS can't rely on where it recently was to help figure out where it is now - this could happen if you turn the GPS on a few hundred miles from where it last was on, or if it's been off for a long time. The SiRF star III chipset has a fast time to fix on your location because it has more correlators than other chipsets and so it can figure out where you are faster.

SiRF star III Chipset High Sensitivity

The SiRF star III chipset is reportedly better at holding a signal in low signal areas, like under dense tree cover or where you can’t see a lot of the sky clearly, like when you are traveling in a downtown area where there are a lot of sky scrapers. SiRF cites that the chipset can track signals down to -159 dBm, and has 200,000 correlators, which by comparison some other chipsets had only a few thousand. Garmin recently upgraded their ForeRunner line to include a couple of improvements to enhance the reception because the original models were sometimes losing satellite reception in these tough areas. The Forerunner 201 series had the satellite receiver along the forearm that didn’t always face the sky when you were using it – like when you were running. The new Forerunner has the GPS satellite receiver mounted on the wrist bone so that in a normal running stance the antenna faces the sky. They also upgraded to the SiRF star III chipset in the model that will help with this issue.

SiRF star III Chipset Longer Battery Life

The SiRF star III chipset is also very efficient, which means low power draw and longer battery life for the unit it is in. Many of the models that are using the SiRF star III chipset are mobile devices that are turning in great battery life times as a result of the lower power draw of the SiRF star III chipset.

 What is XTrac ?

XTrac is a firmware on the SiRF chipset that will boost the sensitivity of a GPS receiver. It does so by acquiring more signal from weaker satellites before it calculates your position.

►So what is XTrac ?  

XTrac is a firmware on the SiRF chipset that will boost the sensitivity of a GPS receiver.  It does so by acquiring more signal from weaker satellites before it calculates your position.  For example, a normal GPS will acquire signals from 4 satellites with the strongest signals to calculate your position.  In the XTrac mode, the GPS will acquire signals from 2 more weaker satellites (total 6 satellites) before outputting a position.

GPS receivers with XTrac chipset:


Holux CF GPS GM-270, GR 230, 231



►SiRFstar IIe

The standard in performance and flexibility for high volume GPS chip sets.  The SiRFstarIIe was the first product to use the SiRFstarII architecture - setting the standard for GPS performance. It features 1920 time/frequency search bins, integrated WAAS, EGNOS, DGPS.

►SiRFstar IIe/LP


The new lower power standard for high volume GPS chip sets. the SiRFstarIIe/LP provides an innovative way to add location awareness to your product. Drawing only 60mA in full power and 20mA in TricklePower, the SiRFstarIIe/LP is one of the lowest power full-feature GPS chipsets on the market.


►SiRFstar IIt

The host-based GPS chip set solution.  SiRFstarIIt makes it easy and economical to add high-performance SiRFstarII technology to systems that are based on many popular processors and operating systems.



The worlds first A-GPS Multimode technology enabling E-911 and LBS platforms.  With the potential of Location Based Services (LBS) and the requirement to meet the enhanced 911 (E-911) mandate, the importance of implementing a location solution is on the increase - for service providers and handset manufacturers alike.  


Autonomous high-sensitivity software designed to extend the range of GPS.  Complimenting SiRF's existing product line of GPS solutions, SiRFXTrac is a high sensitivity GPS software solution.

  • What is Bluetooth?           

Bluetooth is a radio frequency based cable replacement technology. It is designed to be an inexpensive wireless personal networking system for all classes of portable devices such as laptops, PDA`s (Personal digital assistants), mobile phones and headsets. Bluetooth can also replace cabling in a more static environment i.e. between desktop computers and printers. A device has to be Bluetooth enabled (i.e. contain a Bluetooth chip) to be able to use a Bluetooth connection.

  • What is the range of Bluetooth

Bluetooth devices can be in 3 different power classes:

Class 3 : The lowest power, the max. range of this is 10m (30 feet)
Class 2 : Max range is about 50m (150ft)
Class 1 : Max range is about 100m (300ft)
*These ranges can be affected by environmental conditions i.e. furniture, walls, people so ranges can easily be reduced. Bluetooth is not a line of sight connection so it can be used through walls and floors.