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The difference between passive and active antennas

The passive antenna, which has only one ceramic piece to receive satellite signals from the sky, is a pure metal body; No feeding is required during use, but feeding does not affect use; Poor resistance to electromagnetic interference. When used, RF matching (impedance matching) is required, because the general passive antenna is not the standard 50 ohm impedance, if it is not matched, the received signal will be weak, and the receiver may not be able to locate. In addition, when the passive antenna is used, an amplifier circuit can be added to the periphery of the module to ensure that the module can receive a good signal. The active antenna is to add signal amplifier after the passive antenna to improve the sensitivity and improve the signal-to-noise ratio; When used, it must be fed through the receiver board or the receiving module, and the signal amplifier can only work under the power supply condition. Different active antennas have different requirements on the range of feed voltage, so it is necessary to select the appropriate feed voltage according to the antenna parameters.

Common antenna types and scenarios for different types of antennas

Commonly used antenna types are high precision measurement antenna, (four-arm) spiral antenna, patch antenna; Among them, the patch antenna has many different sizes (25X25mm, 18X18mm, 15X15mm, 12X12mm). High precision measurement antenna, due to its large size and high price, is only suitable for test use, not suitable for the final product; It can be used in scenarios where installation space is sufficient and cost requirements are not high. Spiral antenna, the vertical shape of the spiral antenna is high sensitivity, belongs to the omnidirectional antenna, in the direction near the ground plane also has a high antenna gain, so it is easy to be affected by multipath; Suitable for hand-held and human wearable devices, the direction of the antenna can be installed arbitrarily. The black-box antenna, that is, the patch antenna, is simple in structure and cheap in price, but its ability to receive low elevation satellites near the ground plane is relatively poor, and it is also conducive to anti-multipath. The performance of different size patch antenna varies greatly. Note: The MXT906A centimeter-level navigation and positioning module has certain requirements for the antenna, and only the antenna with good performance can achieve centimeter-level positioning accuracy under certain conditions.

Can several EVK/ modules connected to the same power divider feed the active antenna at the same time

When using a power splitter, only one EVK/ module board can feed the active antenna; If multiple EVK/ modules feed the antenna at the same time, the current will be recharged to the EVK/ module, causing the EVK/ module to fail to work properly, and the module may be seriously burned.

Description of the serial port baud rate and the difference between the default baud rates of different products

Mengxin module products support the baud rate of 9600, 19200, 38400, 57600, 115200, 230400; Each module product has its own default output baud rate, see the user manual for each product.

After the receiver is connected to the serial port of the computer, there is no data output or output garbled characters. How to check the cause

After the receiver is connected to the power supply, serial port, and antenna, the serial port has no data output or output garbled characters. The possible causes are as follows: Verify that the baud rate is correct, first try the default baud rate; Check whether the receiver power supply is normal, and check the main power input pin of the module through a multimeter or oscilloscope to determine whether the power supply and voltage are normal; Check whether the serial port is correctly connected and the serial cable is normal. Confirm whether the module is welded properly. After power-on, observe the level of the TXD0 data output pin of the module through the oscilloscope to determine whether the module has data output.

After the receiver is connected, the captured satellite signal is weak or can not capture the satellite signal possible reasons

Check whether the front of the non-omnidirectional antenna is facing up; Check whether the antenna is fed, the active antenna must be fed through the EVK board or module to receive satellite signals normally; Confirm whether the radio frequency part of the receiver is normal through the signal of the known power of the simulator; Whether there are interference sources in the environment where the antenna is located and whether the environment is heavily shielded. Cold start (including ephemeris assisted cold start), hot start: Cold start (ephemeris-assisted cold start) and hot start are indicators used to measure the time from starting the receiver to obtaining positioning results. Cold start means that there is no effective ephemeris, almanac, approximate position and time information inside the receiver when it is powered on. Ephemeris assisted cold start means that the receiver synchronously receives ephemeris information from the outside for fast calculation and positioning. Hot start means that there is a valid ephemeris, almanac, approximate position and time in the receiver. When the receiver is started, the latest position of the current receiver is obtained and calculated based on the above saved content.

Acquisition sensitivity, tracking sensitivity

Capture sensitivity refers to the lowest received signal level when the receiver's output positioning information meets the requirements within a specified period of time. It is divided into cold start acquisition sensitivity, hot start acquisition sensitivity and recapture sensitivity, where recapture sensitivity refers to the lowest received signal level when the receiver output positioning information meets the requirements when the signal is restored after the signal is interrupted. Tracking sensitivity refers to the lowest received signal level that the receiver can maintain stable positioning and meet the accuracy requirements after capturing the signal.

Single mode positioning and dual mode positioning, single frequency and dual frequency

Single-mode and dual-mode refer to the number of satellite systems received by the receiver at the same time. In single-mode positioning, the receiver only receives GPS satellite signals or Beidou satellite signals for positioning calculation; in dual-mode positioning, the receiver simultaneously receives GPS and Beidou satellite signals, and the satellites of both GPS and Beidou systems participate in the calculation and positioning simultaneously. Single-frequency and dual-frequency refers to the number of frequency points of the satellite launched by each satellite system, single-frequency receiver means that the receiver only receives the signals of GPS and Beidou one frequency point each, and the common receiver only receives GPS L1 frequency point and Beidou B1 frequency point. Dual-frequency receiver means that the receiver can simultaneously receive the signals of GPS and Beidou two frequency points, some dual-frequency receivers can simultaneously receive GPS L1 and GPS L2 two frequency points, and Beidou B1 and Beidou B2 two frequency points.

Difference between 3D positioning and 2D positioning

3D refers to the use of at least 4 or more satellites to complete the positioning, positioning information including longitude, latitude, elevation. 2D means that the receiver has only three satellites for positioning, and the elevation value uses a constant to solve the longitude and latitude information. At this time, the elevation value is not accurate. Or, after 3D positioning, the number of satellites is reduced to only 3, the elevation value remains the last value of 3D positioning, and the longitude and latitude positioning are carried out. 3D positioning is more accurate than 2D positioning. Note: MXT products do not achieve 2D positioning.

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