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The most complete wireless intercom intelligent system solution and fault analysis

Views:5     Author:Site Editor     Publish Time: 2020-02-08      Origin:Site


With the rapid development of wireless communication technology in China, the degree of intelligence of urban buildings is getting higher and higher, modern buildings generally have complex structures, and the walls are more shielded from signals. The intercom itself cannot meet the call requirements, and a large area of blind spots has appeared. People have put forward higher requirements on issues such as signal quality, call security, and system capacity of wireless communication inside building facilities. Building wireless intercom communication system is an indispensable part of the building intelligent system. After several generations of technical improvements and innovations, it should be developed into a new brand of digital relay technology, low-power antennas, multi-point distribution, and global signal coverage. Digital communication system, with stable communication security and powerful integrated dispatching functions, greatly facilitates the daily work of relevant departments, and plays a key role in unified dispatch and command of personnel and centralized deployment of resources when emergencies and unexpected events occur. Many fields are widely used in various industries.


System function


1.1 With single call, group call, group call functions: suitable for flexible scheduling of dispatchers. Better call quality: Digital walkie talkies have better call quality than analog walkie-talkies in the same coverage area, especially when working in noisy environments. Digital walkie-talkies can filter out background noise and make the other party hear more clearly. Sound quality.


1.2 Equipped with intelligent lithium battery, with longer talk time: Standard 1500mAh smart lithium battery, the talk time is increased by 40% compared with the lithium battery of the same capacity, and it has automatic repair function, which is more convenient to use.


1.3 Larger capacity and more frequency saving: Only use the frequency of 12.5KHz channel spacing.


1.4 A digital repeater is equivalent to two analog repeaters, allowing two groups of people to talk at the same time. This feature can be used to set up one channel for financial escrows and another channel for security services, so that the communication between the two groups does not interfere with each other, and even between different groups, they do not interfere with each other.


1.5 has high waterproof performance and explosion-proof models: in line with strict IP57 waterproof performance (30 meters for 1 minute under water), it can work normally in rainy or harsh environment, and can ensure smooth communication even in the harshest environment . The selection of explosion-proof models can ensure the safety of on-site production and rescue personnel.


1.6 Digital / analog dual-mode operation to ensure that the equipment is compatible with analog two-way radio equipment: the two-way radio and car radio can be compatible with both digital and analog modes, which facilitates timely communication between the two-way radio and car radio and other units or organizations.


1.7 Built-in GPS positioning function of handheld radio: ensure that the leader or dispatcher knows where each car and each person is located.


1.8 Walkie-talkie monitoring function: The dispatcher or leader can turn on the target walkie-talkie in the form of sending instructions, which is convenient for monitoring the live activities of members.


1.9 Walkie-talkie check function: Dispatchers can check the walkie-talkies of non-responding members and promptly remind members who have not turned on to turn on the walkie-talkie to ensure that each member can communicate smoothly when performing tasks.


1.10 With emergency alarm function: When a team member encounters an emergency, just by pressing the emergency button, the dispatch center can receive a distress signal and understand the specific location of the member via GPS to facilitate other members' emergency rescue; At the same time, the dispatcher can monitor the live activities through the radio monitoring function.


1.11 support short message: support center dispatchers send or receive instructions or prompts via SMS.


1.12 Confidential calls: The inherent security of digital encryption technology can prevent criminals from using the scanning device to eavesdrop. When an illegal user is scanning, he can only hear the channel is working and cannot hear the content of the call. Other members cannot monitor during a group call, ensuring the security of internal calls.


1.14 has wireless bluetooth and wireless headset answering intercom function.


1.15 walkie talkie has the function of wireless patrol stick, which can perform punching positioning function at the patrol point.


System composition


The system consists of dispatching station, repeater, power splitter, coupler, splitter, combiner, signal trunk amplifier, dispatching alarm linkage software, digital walkie-talkie (including backup battery), headset, patrol point, and vehicle station ( Center patrol console), vehicle antenna, omnidirectional ceiling antenna, and other equipment and RF cables and high-frequency connectors. This system should be an extremely flexible wireless intercom system that is easy to expand, reliable and easy to maintain.


Design principles


1) On the premise of ensuring the quality system, use the lowest possible cost design scheme;

2) Reasonably set the position, number and output power of the antennas to ensure that fewer antennas and less output power are used to achieve good coverage;

3) Due to frequent high-level switching and high call drop rates, try to achieve uniform indoor field strength and good signal strength in the design;

4) Establish a perfect digital wireless coverage network;

5) At the same time, consider that the construction is easier to achieve and the construction power, especially the reasonable routing;

6) The link meets the carrier-to-noise ratio in the coverage area ≤15dB


3.2 The principle of antenna location. The principle of antenna location is as follows:


1) Concealment guarantee: The antennas between wireless stations should be concealed to achieve a beautiful effect.

2) Feeder length: Under the premise of ensuring concealment, try to choose the position with the shortest feeder length to reduce the loss. Reduce costs for customers.

3) Try not to install it on the top of the building.

4) Easy antenna installation and construction.


3.3 Indoor signal distribution requirements


In order to meet the design requirements and take into account the difficulty of specific construction, the most reasonable route is selected for wiring and placement of repeaters to achieve uniform power distribution in the room. The coverage signal in this solution is evenly distributed by passive indoor distribution devices through feeders. Teleport to each floor. Calculate strictly in accordance with the technical indicators of the device and feeder, and control the indoor coverage entrance power antenna below 15dBm, in compliance with national electromagnetic environmental hygiene standards. An omnidirectional antenna for transmitting and receiving signals is placed on the top of the ceiling, and is connected to a repeater placed in the computer room through a feeder. The wireless signal distribution system transmits and receives signals from the antenna; the output of the repeater in the computer room is connected to the coupler, the coupler and the antenna and Shielded cables are connected (see wireless intercom distribution system diagram for details). The system design enables the signal to be effectively covered in the relevant space area, so that the entire system achieves uniform coverage, the signal is clear, stable and reliable.


3.4 Frequency classification often used in wireless intercom systems


1.   136-174MHz (civilian)

2. 350-370MHz (for public security fire protection)

3. 400-430MHz (civilian)

4. 450-470MHz (for railway)


The frequency is an accurate value in the frequency band, such as 412.125MHz, 422.075MHz. The frequency band is a range of frequencies, for example, the public security band is 350-370MHz, and the civilian 400-430MHz.


Identification of Active and Passive Devices in Wireless Intercom System


1. Two-way radio repeater is a device used to increase the distance of two-way radio communication. When the distance between two two-way radios exceeds the range of the two-way signal radiation, the two-way radio will not receive a valid signal. The function of the relay station is to forward the received signals to complete the relay between the signals.


2. The splitter is to distribute the signals received by the antenna feeder to different repeaters in the system for processing. Of course, there are different professional functions such as amplification gain and high isolation. According to the number of repeaters, splitters include two splitters, three splitters, four splitters, five splitters, six splitters ... up to 16 splitters. .


3. The combiner combines the signals transmitted by different repeaters in the system, so as to save the antenna feed system. Of course, the actual functions such as isolation, road closure and other functions. According to the number of repeaters, the combiners are divided into two-combiners, three-combiners, four-combiners, five-combiners, six-combiners, etc .. The maximum number is 16 Road device. The splitter is basically the same thing. The reverser is the combiner, which is to combine several signals together.


4. In the wireless intercom system, the duplexer isolates the signal received by the antenna feeder from the signal transmitted by the repeater, so that there is no interference. The duplexer is in two frequency bands to realize the receiving and transmitting


Equipment Installation


5.1 Signal source equipment, the signal source equipment is installed in the equipment room; the feeder is led out from the weak current pipeline, and the antenna is installed at the corresponding position. The main feeder at the distribution end is led by the relay station to the power divider, and the cable is laid by the power divider to each antenna. The installation of the repeater requires clean and beautiful appearance. During actual construction, small-scale adjustments can be made according to the specific interior decoration conditions. All components must be well fixed.


5.2 Indoor feeders, indoor feeders use 50-12 ordinary transmission feeders, which must meet the requirements of fire protection; all feeders must be arranged neatly and beautifully, and there must be no crossover, distortion, or damage; the bending radius should meet the feeder's technical indicators; Use cable ties, feeder bases, cable ladders or feeder clamps to securely fix them; feeders in the ceiling are fixed to the keel iron frame in the ceiling.


5.3 Indoor antenna installation, when installing the antenna, you should pay attention to the following:


(1) The antenna position is well connected to the RF feeder in the ceiling, and it is fixed with a cable tie.

(2) The location is in accordance with the design plan.

(3) Keep the appearance of the antenna clean.

(4) The antenna is concealed.


5.4 RF connector installation, the most critical step in the distribution system engineering of RF connector installation. It is an important part of the system index test. Pay attention to the following when installing:


(1) Install strictly in accordance with the installation and operation specifications of the RF connector.

(2) The connection is good, and the insertion loss of the connector should be less than 0.1DB.


5.5 Installation of Coupler and Power Divider


(1) It should be fixed with strapping straps and fixings. It is not allowed to be suspended or placed in a row.

(2) The feeder line connected to this type of device intersects, and the feeder line at a distance of 300 mm from the interface should be fixed.


Wireless intercom weak signal analysis and processing methods


6.1 Troubleshooting tools are as follows


1. Make a set of feeder connector tools;

2. A signal field strength tester; 3.

3. One standing wave instrument;

4. One antenna, several devices and feeders;


6.2 Failure analysis and processing method


1. The device has not been debugged and the RF switch has not been turned on normally. Processing method: Debug the relevant parameters according to the requirements of the specification. The technical manufacturer has set it up and turned on the RF switch;

2. The trunk is not connected, and the branch line is not connected. Treatment method: According to the requirements of the specification, connect the active equipment, connect the passive components of the main phase and the antenna feed system;

3. The feeder head is not made in accordance with the specifications or the connector is loose and fall off, the aluminum core inside the feeder is too short; treatment method: construction according to the requirements of the specification, the connector is remade, the vertical trunk needs to fix the trunk and components;

4. The device is reversed, the inlet is connected to the outlet, and the outlet is connected to the inlet. Processing method: Connect passive components according to the requirements of the specification, and correctly connect the input and output ends;

5. Water enters components and feeders, causing short circuits. Treatment method: Replace the passive components in the water phase method;

6. The trunk is too long, resulting in weak signal at the end. Processing method: change the main line from the small line to the large line; increase the trunk amplifier;

7. The coupler is connected incorrectly, for example, 15dB is used to 5db; causing the entire rear signal to be too weak. Generally, the devices behind the end of the device are relatively large, and the back becomes smaller. When construction, be sure to follow the design drawings.

8. The frequency band of the passive device is incorrect. The wireless intercom is not in the frequency range. For example, the passive device of the operator is used. Treatment method: Replace the dedicated passive device for wireless intercom.


Wireless intercom system network access permit application process


The wireless frequency band belongs to the country and belongs to the unified management of the Radio Management Bureau. Whenever the wireless intercom system needs to access the wireless frequency band, it needs to apply for the frequency band to the local radio management bureau (hereinafter referred to as "no commission"). The wireless frequency band needs to pay a certain fee. Generally, the user unit handles the payment uniformly. There is a slight difference in the process of applying for a license. The specific process needs to communicate with the relevant local non-commissioning department. According to the facts, many communities or owners have not applied for the wireless frequency band to apply for network access licenses without commissions, and the commissions are not strictly checked, so many owners will not apply. It is recommended to go to the Commission to apply for relevant network access permits, and if found, the Commission will impose penalties.

 

In summary, the wireless intercom system is one of the very many systems in use. The construction is simple, the cost is low, and the weak electrical system indispensable for modern buildings. Especially for the use of construction sites, communities, hotels, etc., the demand is also very large, convenient for constant communication, easy to use, and is one of the necessary artifacts for engineering personnel.


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