This is a very common problem. When you want to buy GPS devices, you will think of whether to connect the GPS service if you need to pay information. In fact, in addition to the cost of purchasing GPS -related software and hardware, using GPS does not need to pay any information fees. The GPS system is just like the broadcasting system. The radio base station constantly launch the broadcast signal. At any time you only need to open the radio to listen to the broadcast program. The maintenance costs of the GPS system are jointly borne by the US government and some large enterprises, and end users do not need to pay service fees. Because the United States created the GPS system, it was only used by the United States at first. In 1984, the GPS system was disclosed, and then it was gradually used for civilian use. Today, it has become a global GPS system.

　　When selecting the GPS receiver, you must first consider whether to support the ST or XT mode. Most of the GPS receivers in the market today use Sirf IIE/LP chipset. In ST mode In some evil circumstances, the GPS receiver cannot receive sufficient signals, and the situation of loss of location information will occur.

　　To correct this problem, new firmware XTRAC appears as XT. The zero -bound point of the minimum signal in the XT mode is smaller than the standard ST mode. It can also track the positioning when the signal is weak, and the signal loss is solved within a certain range, but the new problems that are also generated, such as driving, may be during driving. As a result, you will miss the turning or drift in the road in the road. In order to solve the new problems, the XT V.2 version has appeared again, which has revised the minimum limit of the critical point of the signal. On the other hand, the delay is still not as good as the XT mode.

　　The ST and XT2 models have a common market share. That model is better. According to the application field, the XT2 mode is generally better than the ST mode. It only takes a short time to complete the positioning. In addition, it also has a good signal. Sensitivity. However, the disadvantage is also obvious that the accuracy of the positioning is reduced, and EGNOS is not allowed to improve the accuracy. The knowledge of Waas and EGNOS will be explained in the subsequent chapters. In most cases, this feature is not very related to users.

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