The positioning accuracy of the GPS module lies in many aspects, such as the clock error and track error of the communication satellites from the GPS system, the number and geometric distribution of GPS satellites, solar radiation, the earth's atmosphere, multipath effects, etc. In addition, the same GPS module will have different position errors due to factors such as antenna and coaxial cable quality, antenna position and direction, detection time range, open sky range and orientation, weather, PCB design and other factors. Even if the GPS module of the same manufacturer and the same model are different, when the antenna diversity device is used for detection at the same time, there will be some differences in the amount of static data drift.
The GPS module is often used as a time reference in practical applications. In addition to the internal RTC of the module, a very high-performance time reference can be obtained, which brings great convenience to product design. For the GPS speed limit, it is just an extended application that is realized by performing corresponding calculations on the premise of obtaining geographic coordinates.
(Beitian GPS module BK-450)
The more common antenna for GPS is the porcelain tablet antenna. This type of antenna is low in cost, with an external active amplifier circuit. The receiving signal has a single direction and a relatively high gain, so it is widely used. But its disadvantage is that it is large in size and will cause frequency shift due to the influence of ambient temperature. If the total area of the porcelain is made small, it will affect the receiving gain; if it is made thin, it will affect the receiving bandwidth of the receiving antenna, and it will also be affected by the active amplification part . The size that works well at this stage is 25×25×4mm3. The effect of the ceramic chip antenna is the best when it is placed vertically upwards in actual use.
The GPS antenna signal transmission line is also crucial, including external feeders and PCB traces. Power is only possible if the impedance is matched**. Therefore, all transmission lines must ensure 50Ω high-frequency characteristic impedance. Regarding how to design the RF trace characteristic impedance on the PCB, there are some tools and software that can help to calculate it very conveniently.