I,The factors that affect the wireless communication range:
1, Geographic environment
The furthest communication distance is at the sea level, the flat land and barrier-free open ground. This is also the geographic conditions that commonly used to assess the communication distance of wireless communication devices. Followed, are some half-barriers such as the suburban and rural areas, hills, river, semi-open environment. The nearest communication distance is in the city-rise buildings or mountains. In short, the more dense barriers, the greater impact of wireless communications distance, especially the metal objects.
2, Electromagnetic environment DC motor, high-voltage power grids, switching power supplies, welding machines, high-frequency electronic devices, computers, microcontrollers and other equipment for wireless communication devices have different communication range extent.
3, Climate conditions
The communication distance can be longer when the air is dry. The communication distance can be shorter when the air is moist (especially rain and snow).In the environmental operating temperature range that the product allowed, the temperature rise will lead to reduce transmission power and reduce the reception sensitivity, thus reducing the communication distance.
4, The transmitter RF output power
The larger transmission power is, the greater communication distance. But in fact, due to the cost, the transmitter output is limited.
5, The receiver sensitivity of the receiver
Receiver sensitivity reflects the ability of the receiver to capture weak signals. The higher of the receiver sensitivity, the farther communication distance.
6, The anti-jamming capability of the system
The actual communication environment, there is always a variety of interference sources, in the same transmitter power and receiver sensitivity, the stronger anti-jamming capability, the farther actual communication distance. However there are many factors that impact the wireless communication systems anti-jamming ability. Primarily with the modulation / demodulation mode, bandwidth, circuit design, PCB board layout and decoupling, and shielding measures are properly related. In general, FM system, excellent anti-jamming capability VSB systems, while the narrow-band system anti-jamming capability is superior to broadband system, therefore, the more narrow bandwidth, the stronger anti-interference ability, in the same transmit power and receiver sensitivity conditions, the farther communication distance.
7, The software error correction
With the system of software correction, its communication distance can be farther than without the software error correction. Software error correction can improve the receiver sensitivity 1-3dB, but it would produce a certain delay, in demanding real-time systems must to consider the factors.
8, Antenna type and gain
The higher antenna is, the farther communication distance. When the transmitter use high-gain directional antennas, it can significantly improve the communication direction of the power density (field strength). The receiver uses a high gain directional antennas can significantly improve the signal / noise ratio and improve the reception field strength, thus to dramatically improve communication distance. Currently, the antennas suitable for ISM / SRD band-free license to use wireless communication devices are the following:
Whip antenna (helical antennas, rod antenna): Gain 0 ~ 3.5dB, suitable for portable mobile hand-held machine
The gain sucker Antenna: gain of 5.5 ~ 7dB, for a fixed machine and vehicle
High Gain Omni-directional Antenna: gain 8.5 ~ 10dB, need outdoor installation, fixed network unit
High-gain directional antenna: gain of 10 ~ 12dB, need outdoor installation, suitable for long-distance fixed-machine
Need to note is that: the higher gain antenna has the larger geometric dimensions. In particular, high-gain directional or omni- directional antennas require outdoor installation in order to play their best. Therefore, need to consider the installation and using convenience when choose antenna.
9, The effective heights of antenna
A variety of conditions are the same, the higher of antenna height from the ground plane, the farther communication distance. Especially in the urban environment, Raising the height of the antenna can be much greater impact the communication distance than increasing the transmit power.
II, Improve communication distance measures:
1, To maximize the effective height of antenna
Communication distance and the square root of the product of the effective height of T/R antenna is proportional. Improving the antenna effective height can significantly expand the communication distance, especially in the urban environment, setting the antenna in the roof can avoid a lot of obstacles and away from sources of interference, thus, expanding the scope of communication.
2, Use high-gain antenna
Antennas are passive devices, which itself can’t amplify the signal, but the high-gain antennas can significantly improve the communication direction of the energy density, improve the signal / noise ratio, then, expanding the scope of communication. Its role is similar with the flashlight searchlight condenser.
Transmitter using high-gain directional antennas can significantly improve the communication direction of the signal strength. The receiver uses a high gain directional antennas can significantly improve the communication direction of the received signal field strength and signal / noise ratio. Thus significantly expand communication distance. But only for the same direction communication, and the cost is quite high, the antenna geometry large, weight is also heavier, only suitable for fixed installation.
3, Try to shorten the length of RF cables
The RF coaxial cable which is used to connect to the wireless communication equipment and an outdoor antenna has a certain degree of loss RF signals. For example, 50-3 cable loss of 0.2dB / m, 50-7-type cable loss of 0.1dB / m , 50-9-type cable loss of 0.07dB / m. The longer of the cable is, the greater loss. The increase of the loss transmit RF signal will lead to a decline of the communication distance. Therefore, RF components can be mounted directly to the bottom of the outdoor antenna when it is necessary. The connection between the RF components and user's system is a multi-core shielded cable.
4, Away from the interference sources
the closer from interference sources, the lower of signal / noise ratio and also will lead to decline the communication distance. When it is necessary can respectively take shielding measures to the number of transmission modules and the components that will produce electromagnetic interference. It can make the antenna far away from interference sources to use 50Ω RF characteristic impedance coaxial cable. At the same time, power cable which connect to the RF components and signal cable also use shielded cable. And also plus the necessary filtering network so that greatly suppress interference and improve the receiver high sensitivity.
5, Priority use strong anti-interference ability wireless receiver
When the wireless communication receiver work in the big electromagnetic interference environment, but you can’t keep up anti-jamming capability, the receiver sensitivity will become meaningless. At this time, You should give priority to products with a strong anti-interference ability. Such as the narrow-band second frequency FM or FSK / GFSK modulation / demodulation mode products
(Usually this type of product also has very high receiver sensitivity).If it is digital communication system, you should give priority to the software products with error-correcting function.
6, Lightning protection, waterproof, moisture-proof
If use of outdoor antenna system, must take lightning, lightning protection measures, such as installing lightning rod and lightning arrester.
At the same time, for an open-air overhead power supply cables and signal transmission cables should also be taken lightning protection measures to prevent lightning from the cables into the machine.
1 字段 2 字段 3 字段 4 字段 5 字段 6 字段 7 字段 8 字段 9 字段 10 字段