What Is a GPS PDA?

GPS is a terminal for positioning or navigation by receiving satellite signals. To receive signals, an antenna must be used. GPS satellite signals are divided into L1 and L2, with frequencies of 1575.42MHZ and 1228MHZ, respectively, of which L1 is an open civilian signal, and the signal is circularly polarized. The signal strength is about -166dBW, which is a relatively weak signal. These characteristics determine to prepare a special antenna for GPS signal reception.

GPS antenna

GPSFrom the polarization mode, GPS antenna is divided into vertical polarization and circular polarization.

With current technology, vertical polarization is not as effective as circular polarization. Therefore, except for special cases, GPS antennas will use circular polarization and linear polarization.

GPSThe GPS antenna is divided into built-in antenna and external antenna in terms of placement.

The mounting position of the antenna is also very important. Early

The following factors affect the GPS antenna performance:

1. Ceramic sheet: The quality of the ceramic powder and the sintering process directly affect its performance. The ceramic sheets currently used in the market are mainly 25 × 25, 18 × 18, 15 × 15, 12 × 12. The larger the area of the ceramic sheet, the larger the dielectric constant, the higher the resonance frequency, and the better the acceptance effect. Most of the ceramic plates have a square design, to ensure that the resonance in the XY direction is basically consistent, so as to achieve the effect of uniform star collection.

2. Silver layer: The silver layer on the surface of the ceramic antenna can affect the antenna resonance frequency. The ideal GPS ceramic chip frequency accurately falls at 1575.42MHz, but the antenna frequency is very susceptible to the surrounding environment. Especially when assembled in the whole machine, the frequency must be adjusted to maintain the frequency at 1575.42MHz by adjusting the shape of the silver coating. . Therefore, the GPS machine manufacturers must cooperate with the antenna manufacturers to provide complete machine samples for testing when purchasing antennas.

3. Feed point: The ceramic antenna collects the resonance signal through the feed point and sends it to the back end. Due to the impedance matching of the antenna, the feed point is generally not in the center of the antenna, but is slightly adjusted in the XY direction. Such an impedance matching method is simple and does not increase cost. Moving only in the single-axis direction is called a single-biased antenna, and moving in both axes is called double-biasing.

4. Amplifying circuit: The shape and area of the PCB carrying the ceramic antenna. Due to the characteristic of GPS ground bounce, when the background is 7cm × 7cm uninterrupted ground, the effectiveness of the patch antenna can be maximized. Although constrained by factors such as appearance and structure, try to keep a considerable area and uniform shape. The gain of the amplifier circuit must be selected to match the back-end LNA gain. Sirf's GSC3F requires that the total gain before signal input does not exceed 29dB, otherwise oversaturation of the signal will generate self-excitation.

The GPS antenna has four important parameters: gain (Gain), standing wave (VSWR), noise figure (Noise figure), and axial ratio (Axial ratio). Among them, the axial ratio is particularly emphasized, which is an important indicator for measuring the difference of the signal gain of the whole machine in different directions. Since the satellites are randomly distributed on the hemisphere sky, it is very important to ensure that the antennas have similar sensitivity in all directions. The axial ratio is affected by antenna performance, appearance structure, internal circuit of the whole machine, and EMI.

The manufacturers that can produce GPS ceramic antennas by themselves are mainly Da Gamma navigation,

Most GPS antennas are right-handed polarized ceramic dielectrics, and their components are: ceramic antennas, low-noise signal modules, cables, and connectors.

The ceramic antenna is also called passive antenna, dielectric antenna, and PATCH. It is the core technology of GPS antenna. The signal receiving ability of a GPS antenna depends largely on the composition of its ceramic part.

The low noise signal module, also called LNA, is the part that amplifies and filters the signal. Its component selection is also very important, otherwise it will increase the reflection loss of the GPS signal and cause excessive noise.

The selection of cables should also be based on reducing reflections to ensure impedance matching.

1.GPS can't be positioned 100%, let alone believe in indoor positioning. The GPS does not broadcast like a mobile phone. It can receive signals anywhere. Many things will affect GPS reception, including the distribution of sky stars, buildings, viaducts, radio waves, leaves. , Thermal insulation paper, etc., will affect too many things. Generally speaking, looking up from the GPS position, you can see the area of the sky, which is the area where the GPS can receive signals.

2. Don't use it once or twice, or one or two days, to determine the quality of the GPS-because the status of the sky satellites is different every day, maybe the same place, the reception is full in the morning, but it is impossible to locate at night, it is possible, it is possible Positioning was bad for days.

3. To compare the quality of GPS, you must compare it at the same place at the same time-many people new to buy GPS, will say, the one I used before is better or something like that, but this is not true, because the time and place are different, and finally The results are much worse, and must be used for a long time, or at the same time at the same time, in order to feel the difference between the two GPS.

4.The GPS receiving intensity table is no longer sufficient as a reference for GPS purchase-everyone buying GPS will only look at the receiving table in the electronic map. It may have been accurate before, but the current GPS is for the receiving table to see It looks good, so there are fake signals, or simulated signals, etc. The reception table is really beautiful, but it may not be positioned correctly, and it may not even be displayed correctly.

5. There is no so-called indoor positioning GPS-basically there is no signal in the room, but there is no signal. For true indoor positioning, you must be indoors from the cold start, but the same can be positioned, which is the true indoor positioning. No, because I don't navigate at home.

6.When purchasing GPS, you don't need to choose the brand as the purchase option, but you can choose the chip used internally-basically, there are many GPS manufacturers, and the choice of the manufacturer is only for after-sales service. Not the big manufacturers must be the best. Talking about the GPS of the same chip, different manufacturers do, the effect will not have much difference, so if you choose the GPS without choosing the brand, you can choose the GPS receiving chip.

7. Do you want to use Bluetooth, CF gps, or gps mouse?-Generally speaking, this is a matter of opinion. When using Bluetooth or CF, you must worry about gps or pda being out of power at any time, and the cost is high, but you can always Navigation anywhere, using GPS mouse is economical and good reception, you don't have to worry about power issues, but the cable is troubled.

8. The positioning is not accurate, it may not be a GPS error-basically the positioning error can be within 20 meters, which is considered a good GPS. In addition, the GPS position is not very accurate on the road, there may be many reasons, and poor reception may cause The error may be a problem with the map data or a wide road, so it seems that the GPS is stably offset from the road. After a long time, you know whether it is a GPS or a map problem.

9.Buy gps, the specification table is for reference only-what the GPS specifications are to complete the positioning within a few seconds, what are the meters of error, sensitivity, and other information, these are written well, you must know the real use, seriously, compare the specifications Table is a waste of time. 10. Use GPS, no need to charge communication fees-although everyone knows, some people still think that they need to charge another monthly fee.

11. When the store says that xxx GPS is not good, don't believe it too much-it may be that the store is no longer sold, or there is a large inventory of other things, it is recommended that you buy another GPS. 12.GPS can be placed inside the car-except for external antennas, things like gps mouse, can be placed inside the car, because the gps is waterproof, but it is unavoidably hung outside for a long time. When you order it, you need to collect it when you get on and off the bus, but it will be dried when placed outside. It is recommended to choose grid heat paper carefully, or cut a hole in grid heat paper, and paste other things. Not ugly anymore.

13. If the GPS is newly purchased for the first time, or it is already in the cold start state, please go to the open space for fixed positioning outside the car-this way, the positioning speed is faster, and there will be no strange phenomenon. Go straight to the road in the cold start state, even if the signal is very strong, you may not be able to locate it when you reach the destination !! This is very important. After positioning, put it in the car and see if the reception in the car will be compared. Poor, in addition, the longer a single GPS is used, the longer it can save satellite data. If it is not used for a long time, such as one to two weeks, the GPS may return to the cold start state. The above is for everyone who is new to satellite navigation. I hope that with these mental preparations, I will not feel that satellite navigation is not easy to use. Basically, as long as you can reach your destination, satellite navigation is very useful for you. As for whether it is relatively time-saving and whether the journey is relatively short, do not ask too much, basically go to an unfamiliar place, as long as you can reach the place smoothly, maybe there will be some nonchalant planning in the journey Take some paths, but over time, you will understand the characteristics of current satellite navigation, and it will not be so uncomfortable to use. Of course, the map manufacturers still need to work hard, but I hope everyone can give the manufacturers appropriate encouragement. The purchase of genuine copies is the best support.

GPS antenna electrical characteristics

1.1 Antenna

Antenna model / antenna model

Dagama GPS-A130

Frequency Range

1575.42MHz ± 1.02 MHz

VSWR / standing wave ratio

1.5: 1

Band Width

> 10 MHz

Impendence

50 ohm

Gain / gain

5dBic Based on 7 × 7cm ground plane

Polarization

RHCP

1.2 LNA / low noise amplifier

Frequency Range

1575.42MHz ± 1.02 MHz

DC Voltage / DC voltage

3.0-5.0V

Gain (Typical)

29dB (+ 25 ± 10 )

Output VSWR Typical / Output standing wave

<1.5

Noise Figure (Typical)

1.5 (+ 25 ± 10 )

DC current (Typical)

15.5mA (At 3.0V)

GPS antenna material

Antenna / antenna

Dielectric Ceramics / Dielectric Ceramics

PCB / printed circuit board

FR4

Shielding

Tinplate

RF Cable / RF cable

RG174 300 ± 10CM

RF Connector / RF connector

SMA-J3

Thickness / thickness

15.5mm